Help with misfiring on my 1997 5.0L Explorer.

thegirlin48127 · 08-12-2011, 07:21 PM

I was wondering if anyone knew when the ignition coils should be replaced ....
The truck chuggs when you push down on the accelerator and when I took it to the shop they hooked it up to the scanner and it said it was in need of a tune up and it was misfiring, that the O2 sensors are bad and something to do with the egr (either valve or solenoid).
I have replaced the TPS sensor, pcv valve, spark plugs, the EGR valve and EGR vaccum solenoid, cleaned the MAFS and Throttle body. I have also replaced all of the O2 sensors. It has 220,000 miles on it and I believe it has the original engine in it but thats just a guess..I know that the trans was rebuilt a few years back. Its a 1997 explorer 5.0 and it was running great till this happened...

lil'mounty · 08-13-2011, 12:30 PM

This is CRAZY! I have been battling the same thing in my 97 5.0L Mountaineer (179,000mi). Chugs up hills, misfires and acts like its 'slipping' on heavy acceleration. And no codes! I replaced the trans. solenoids, TPS, plugs, wires, PCV, and checked to see if the cats were clogged. I was going to tear into the EGR system but decided to just do the coils for $100/pr (autozone) because I can hear cyl#3 tick (in the pass. wheelwell) after it warms up trying to fire. My thoughts are after the coils warm up voltage drops. Does yours tick after idling for ten minutes? You just reinforced my thoughts to try coils before the EGR. I will let you know how the coils go.

lil'mounty · 08-13-2011, 03:42 PM

Replaced the coils... They were still the originals. Still misfires. Next I will check fuel pressure.

explorinitup · 08-13-2011, 04:36 PM

I second that. Start with coils.

thegirlin48127 · 08-13-2011, 04:44 PM

I replaced the coils still no improvement... I was thinking maybe it would be a fuel injector (either dirty or clogged) ...does anyone have any thoughts on this... I was going to sea foam it but I'm kinda apprehensive about putting it into the vaccum line (I don't need any more problems with it) Does anyone have any experience with sea foam? I've heard that it ruins your spark plugs and O2 sensors and may clog your cat. converter...

lil'mounty · 08-13-2011, 10:56 PM

Hear we go... I seafoam on a regular basis. Silicone KILLS your o2 sensors and there is no silicone in seafoam (its mainly kerosene) thats why it says "o2 safe"...no silicone. I usually seafoam through the PCV system and use A THIRD of the can, more then that can cause plug fowling. And make sure it 'slurps' air w/ the seafoam (to avoid vaporlock). With that said, two weeks ago I seafoamed through the intake (for the first time) and I think I may have dumped all the built up carbon in the manifold into my cylinders. That is why I checked for clogged cats! I can feel a huge power gain but it still misfires... as it did before. Did you ever change your wires?

thegirlin48127 · 08-13-2011, 11:20 PM

I replaced the wires last time I did the tune up and I was thinking of doing it this time also but haven't yet... I read somewhere that if your cat is plugged then you can drill holes into it to let the pressure out (but of course you would have to replace them...) I was thinking the same thing about the clogged cats. and muffler (I know that thing is falling apart and may very well be the problem) Its just trying to find a needle in a haystack at this point and is becoming a money pit.... I'm going to use carb. spray tomorrow and look for vaccum leaks .... it runs smooth unless there is too much pressure built up behind it (like if you step on the gas) and thats where it starts chugging and shifting wierd ... but if you give it steady gas it shifts great and has no ill symptoms .... do you think it'll hurt it if I sea foam it in the throttle body and the vaccum line where the pcv valve is in the same day?... I was just thinking that maybe the intake manifold is clogged up somewhere also and if I do the throttle body then it will hopefully clean out the intake...

lil'mounty · 08-14-2011, 09:24 AM

Thats how mine was acting (just on hills or under load with to much gas). Now it misfires at idle so I don't drive it far.
CATS- Does yours sometimes make a plunk noise like ignition in the exhaust header? Mine DID. Thats what made me think clog! When I pulled the cats I CLEANED them. I wouldn't drill yet! Once the front pipe/cat assembly is removed, and o2 sensors removed, fill them with a mix of laundry detergent and water and let them sit overnight or longer. It takes some positioning or a tall bucket to get them full. When done rinse them out with a hose. I did it twice. I didn't believe it could work so I cut them open and checked, and it worked! They looked brand new and clear with 170,000 mi. on 'em. Then I welded them shut again and straightpiped the rear cats and replaced the muffler. The plunk plunk noise is gone and it is more responsive but still misfires. You can see the surface of one cat through the o2 hole. Its a big PITA, but its free!
WIRES- If it has been longer then a year I would replace them. Because when heated and cooled the insides get brittle. Then when you move them to do the plugs they can start fouling. Just a thought.
CARB SPRAY- Never did this method, it scares the hell out of me. The thought of spraying flammable liquid around electric and a hot engine doesn't sound cool. Were you able to replace, or see, the vacuum tubes under the intake manifold when you replaced the egr stuff. If those are cracked it could screw up the egr system. I can't even touch/see mine.
SEAFOAM- PCV same day as intake, no that won't hurt, But if this the first time its been foamed you could get a lot cleaned and pushed further down the system. Perhaps do it several times. You will just have to be prepared to replace the plugs again. When I went through the intake, I went through the small hose connection AFTER the MAF and before the throttle body. It is on top and it is just a plastic elbow/hose. It doesn't suck air but it will mix with the air in the intake so take a funnel and slowly poor it in. If you go that route!
I will check my gas pressure today and let you know. I am not saying you should do ALL this stuff but I hate the guessing game too. And hopefully one of the things I mention will help you narrow it somehow. I still didn't throw a code, not even a misfire code.

thegirlin48127 · 08-14-2011, 12:36 PM

The vac hoses seemed fine when I replaced the erg vavle and solenoid ... is it normal for the engines rpm's to increase when you take the vac line off to put it into the pvc line? I really appreciate the advise you gave for washing out the cat converters (I didn't think you could do that)... I'll get to that tomorrow and let you know how it goes. As for the carb spray I was thinking the same thing but sometimes desperate times calls for desperate measures (and sometimes result in a person doing stupid and dangerous things).... as for testing the fuel injectors to see if they are working correctly I was thinking of getting the cheap test tools from auto zone ($25) but I haven't figured out how to get to them (they are not very accessible) any thoughts on this?

lil'mounty · 08-14-2011, 02:01 PM

As for the vac line.. I believe yes. Because if you block that line it should kill the engine (If I remember correctly). My gas pressure is perfect. But I discovered the #4 plug wire route (through the top of the engine block, by the valve cover. was arcing out tic tic tic tic, after it warmed up. I totally disconnected the wire and no change in idle so I think I found my misfire/voltage loss. I am going to reroute it and try to stay away from the exhaust manifold.
So, Where i am sitting right now is I had a clogged cat (pass side) and ended up with a shorting out plug wire after!
I went through codes yesterday individually and my EGR was fine. Do you have any codes?
INJECTORS.. You would have to pull the entire upper intake and individually volt check each injector. I never did it but tried to avoid it!

**BrooklynBay** · 08-14-2011, 03:26 PM

Welcome to this forum! I've moved your thread into the stock 95-01 section.

thegirlin48127 · 08-14-2011, 11:37 PM

I am sea foaming it, changing the wires, replacing the throttle body gasket (I took it apart the other day and found it was bad; the on that goes directly on the intake from the throttle body) and I'll clean the cat converters like you said; removing the O2 sensors before sea foaming it...I don't need any problems with them getting clogged/dirty as well, as they are not cheap @ $50 ea. x 4.... give it a new air filter and hope that'll take care of it... how did it go with yours? have you fixed the issue? ..I know u said you located a faulty wire but I was just wondering if you replaced it and fixed the issue or if I have to keep looking .... I tried taking the wires off of mine but I was taking them off if the coil one at a time till I got zapped ..lol... so I reconsidered my approach ... do you think it would have been a better idea to take them off of the plugs instead? it's just the exaust manifold is right there so I figured it would've been easier to take them off of the coil.... besides burns seem to hurt longer than just getting zapped for a second .... I really appreciate all the feedback lil'mounty...thanks for all the tips

budwich · 08-15-2011, 08:39 AM

First, you should get your fuel pressure tested to see if it is running within spec. Next,IF you think you have a cat problem. Disconnect them and replace with an equivalent length of straight pipe and make a test run to see if things change ... its a cheap and dirty test. IF they tested and found "misfiring", they should have indicated what cylinders were misfiring. IF it wasn't a particular cylinder, then it is unlikely to be a wiring problem, more than likely a fueling issue (air/fuel mixture) OR timing issue (crankshaft sensor and related "stuff").

lil'mounty · 08-15-2011, 09:42 AM

Yes, I am all fixed! My issue was a clogged cat. The second issue (which I created while doing the cat) was the 'stock' route for the plug wire, started arcing against the rear firewall. Originally, I had your exact issue W/O a code (ever), seafoamed it and cleaned the cats. It is a good idea to check your fuel pressure BUT I will bet you have a clogged cat. You will not get a code for that and it is just as important as air IN. If you do check your fuel pressure it should be 32-40 psi. It does take 3 good cycles w/ the key to get the fuel rail up to the spec 32-40 from 0. (It charges like 12 psi a 2 second cycle) but once there it should hold it in that range, running or off or sitting for 30 min. It's just the initial startup after total pressure discharge.
You can drive around without your exhaust (or o2 sensors) to find a hill to try and mimmick the lagging, but I couldn't because laws are kind of strict about that around here.

thegirlin48127 · 08-15-2011, 09:38 PM

I think you just solved my issue too... I looked under there today trying to get the cats off and I see an area where the carbon build up was coming out (because of sea foaming it a bit) it wasn't coming out of the tail pipes so I looked further up the line and saw where it was exiting (on a coupling from a previous issue) ... I'll let you know how it goes tomorrow (I'll be replacing the wires too just to be sure so I hopefully won't have to work on it in the winter time) .... Thanks again for your help

lil'mounty · 08-17-2011, 11:25 AM

Good! The pipes are a real puzzle to get out/in. It helps to remove the t.case skid plate. If your hands aren't small enough the o2 sensor plugs can be accessed through the inside of the vehicle under the center counsel (there is agood write up on this forum somewhere on pulling the center out.. super easy!). I am sure you'll figure it out. Let me know the results.

rjcooperss396 · 08-17-2011, 11:58 AM

Have you guys done a compression test yet? I recently helped my nephew track down a misfire on his '93 F150 and he had 10psi on cylinder 8. A leak down test pointed to an issue with the exhaust valve and this is what I found when I pulled the head.

lil'mounty · 08-18-2011, 12:37 PM

That would not be cool! In looking at the pic, it makes me wonder how it happened. It looks as if the valve hit the pressure gauge. The reason I say that is if it were run for any period of time there would be carbon on the valve seat and valve break area. It's spotless. The plug threads look very shallow compared to some heads. I hate to tell you this but I think you created extra work for yourself. That' just my opinion, but if that is the case don't worry it happens to us all at some point.

rjcooperss396 · 08-18-2011, 12:58 PM

The threaded part of the compression gauge doesn't enter the chamber. My guess is that it burnt the valve and the valve cracked and broke. This is very common in the 302.

lil'mounty · 08-18-2011, 01:27 PM

Makes sense! I wasn't sure how long the gauge was. Another thing is on our gt40 heads, there are issues w/ 302 plug listings at the parts store. I have noticed some list for plugs w/ longer threading. I believe they assume all 302's have the same heads. I don't know what head that is and I don't think that was the case (or all exhaust valves would have cracked) I just thought it would be worth mentioning.

08-12-2011, 07:21 PM	#1
thegirlin48127 Wannabe Elite Explorer wyandotte, Mi. 97 explorer Join Date: Jul 2011 Posts: 10 Vehicle Specs (Original Poster)	Help with misfiring on my 1997 5.0L Explorer. I was wondering if anyone knew when the ignition coils should be replaced .... The truck chuggs when you push down on the accelerator and when I took it to the shop they hooked it up to the scanner and it said it was in need of a tune up and it was misfiring, that the O2 sensors are bad and something to do with the egr (either valve or solenoid). I have replaced the TPS sensor, pcv valve, spark plugs, the EGR valve and EGR vaccum solenoid, cleaned the MAFS and Throttle body. I have also replaced all of the O2 sensors. It has 220,000 miles on it and I believe it has the original engine in it but thats just a guess..I know that the trans was rebuilt a few years back. Its a 1997 explorer 5.0 and it was running great till this happened...

08-13-2011, 11:20 PM	#7
thegirlin48127 Wannabe Elite Explorer wyandotte, Mi. 97 explorer Join Date: Jul 2011 Posts: 10 Vehicle Specs (Original Poster)	I replaced the wires last time I did the tune up and I was thinking of doing it this time also but haven't yet... I read somewhere that if your cat is plugged then you can drill holes into it to let the pressure out (but of course you would have to replace them...) I was thinking the same thing about the clogged cats. and muffler (I know that thing is falling apart and may very well be the problem) Its just trying to find a needle in a haystack at this point and is becoming a money pit.... I'm going to use carb. spray tomorrow and look for vaccum leaks .... it runs smooth unless there is too much pressure built up behind it (like if you step on the gas) and thats where it starts chugging and shifting wierd ... but if you give it steady gas it shifts great and has no ill symptoms .... do you think it'll hurt it if I sea foam it in the throttle body and the vaccum line where the pcv valve is in the same day?... I was just thinking that maybe the intake manifold is clogged up somewhere also and if I do the throttle body then it will hopefully clean out the intake... Last edited by thegirlin48127; 08-13-2011 at 11:24 PM. Reason: had to be more specific on what I was explaining

08-14-2011, 12:36 PM	#9
thegirlin48127 Wannabe Elite Explorer wyandotte, Mi. 97 explorer Join Date: Jul 2011 Posts: 10 Vehicle Specs (Original Poster)	The vac hoses seemed fine when I replaced the erg vavle and solenoid ... is it normal for the engines rpm's to increase when you take the vac line off to put it into the pvc line? I really appreciate the advise you gave for washing out the cat converters (I didn't think you could do that)... I'll get to that tomorrow and let you know how it goes. As for the carb spray I was thinking the same thing but sometimes desperate times calls for desperate measures (and sometimes result in a person doing stupid and dangerous things).... as for testing the fuel injectors to see if they are working correctly I was thinking of getting the cheap test tools from auto zone ($25) but I haven't figured out how to get to them (they are not very accessible) any thoughts on this? Last edited by thegirlin48127; 08-14-2011 at 12:38 PM. Reason: spelling error

08-14-2011, 03:26 PM	#11
BrooklynBay Aerostar Forum Moderator Brooklyn, NY 88 89 93 95 96 Aerostars Join Date: Nov 2005 Posts: 45,813 Vehicle Specs	Welcome to this forum! I've moved your thread into the stock 95-01 section. __________________ My list of useful threads. My photo gallery. My product reviews. My list of items for sale. Aerostar owners thread. Aerostar parts work in Explorers, Rangers, and Bronco II thread. History of the Aerostar thread. Aerostar Forum. New Members Forum. Ford/Lincoln/Mercury Forum.

08-13-2011, 12:30 PM	#2
lil'mounty Wannabe Elite Explorer Cold Wisconsin '97 Mercury Mountaineer Join Date: Mar 2010 Posts: 18 Vehicle Specs	This is CRAZY! I have been battling the same thing in my 97 5.0L Mountaineer (179,000mi). Chugs up hills, misfires and acts like its 'slipping' on heavy acceleration. And no codes! I replaced the trans. solenoids, TPS, plugs, wires, PCV, and checked to see if the cats were clogged. I was going to tear into the EGR system but decided to just do the coils for $100/pr (autozone) because I can hear cyl#3 tick (in the pass. wheelwell) after it warms up trying to fire. My thoughts are after the coils warm up voltage drops. Does yours tick after idling for ten minutes? You just reinforced my thoughts to try coils before the EGR. I will let you know how the coils go.

08-13-2011, 03:42 PM	#3
lil'mounty Wannabe Elite Explorer Cold Wisconsin '97 Mercury Mountaineer Join Date: Mar 2010 Posts: 18 Vehicle Specs	Replaced the coils... They were still the originals. Still misfires. Next I will check fuel pressure.

08-13-2011, 04:36 PM	#4
explorinitup Wannabe Elite Explorer virginia beach, virginia 97 explorer 5.0 Join Date: Oct 2006 Posts: 482 Vehicle Specs	I second that. Start with coils. __________________ ...im sorry officer the truck..she just wants more....

08-13-2011, 04:44 PM	#5
thegirlin48127 Wannabe Elite Explorer wyandotte, Mi. 97 explorer Join Date: Jul 2011 Posts: 10 Vehicle Specs (Original Poster)	I replaced the coils still no improvement... I was thinking maybe it would be a fuel injector (either dirty or clogged) ...does anyone have any thoughts on this... I was going to sea foam it but I'm kinda apprehensive about putting it into the vaccum line (I don't need any more problems with it) Does anyone have any experience with sea foam? I've heard that it ruins your spark plugs and O2 sensors and may clog your cat. converter...

08-13-2011, 10:56 PM	#6
lil'mounty Wannabe Elite Explorer Cold Wisconsin '97 Mercury Mountaineer Join Date: Mar 2010 Posts: 18 Vehicle Specs	Hear we go... I seafoam on a regular basis. Silicone KILLS your o2 sensors and there is no silicone in seafoam (its mainly kerosene) thats why it says "o2 safe"...no silicone. I usually seafoam through the PCV system and use A THIRD of the can, more then that can cause plug fowling. And make sure it 'slurps' air w/ the seafoam (to avoid vaporlock). With that said, two weeks ago I seafoamed through the intake (for the first time) and I think I may have dumped all the built up carbon in the manifold into my cylinders. That is why I checked for clogged cats! I can feel a huge power gain but it still misfires... as it did before. Did you ever change your wires?

08-14-2011, 09:24 AM	#8
lil'mounty Wannabe Elite Explorer Cold Wisconsin '97 Mercury Mountaineer Join Date: Mar 2010 Posts: 18 Vehicle Specs	Thats how mine was acting (just on hills or under load with to much gas). Now it misfires at idle so I don't drive it far. CATS- Does yours sometimes make a plunk noise like ignition in the exhaust header? Mine DID. Thats what made me think clog! When I pulled the cats I CLEANED them. I wouldn't drill yet! Once the front pipe/cat assembly is removed, and o2 sensors removed, fill them with a mix of laundry detergent and water and let them sit overnight or longer. It takes some positioning or a tall bucket to get them full. When done rinse them out with a hose. I did it twice. I didn't believe it could work so I cut them open and checked, and it worked! They looked brand new and clear with 170,000 mi. on 'em. Then I welded them shut again and straightpiped the rear cats and replaced the muffler. The plunk plunk noise is gone and it is more responsive but still misfires. You can see the surface of one cat through the o2 hole. Its a big PITA, but its free! WIRES- If it has been longer then a year I would replace them. Because when heated and cooled the insides get brittle. Then when you move them to do the plugs they can start fouling. Just a thought. CARB SPRAY- Never did this method, it scares the hell out of me. The thought of spraying flammable liquid around electric and a hot engine doesn't sound cool. Were you able to replace, or see, the vacuum tubes under the intake manifold when you replaced the egr stuff. If those are cracked it could screw up the egr system. I can't even touch/see mine. SEAFOAM- PCV same day as intake, no that won't hurt, But if this the first time its been foamed you could get a lot cleaned and pushed further down the system. Perhaps do it several times. You will just have to be prepared to replace the plugs again. When I went through the intake, I went through the small hose connection AFTER the MAF and before the throttle body. It is on top and it is just a plastic elbow/hose. It doesn't suck air but it will mix with the air in the intake so take a funnel and slowly poor it in. If you go that route! I will check my gas pressure today and let you know. I am not saying you should do ALL this stuff but I hate the guessing game too. And hopefully one of the things I mention will help you narrow it somehow. I still didn't throw a code, not even a misfire code.

08-14-2011, 02:01 PM	#10
lil'mounty Wannabe Elite Explorer Cold Wisconsin '97 Mercury Mountaineer Join Date: Mar 2010 Posts: 18 Vehicle Specs	As for the vac line.. I believe yes. Because if you block that line it should kill the engine (If I remember correctly). My gas pressure is perfect. But I discovered the #4 plug wire route (through the top of the engine block, by the valve cover. was arcing out tic tic tic tic, after it warmed up. I totally disconnected the wire and no change in idle so I think I found my misfire/voltage loss. I am going to reroute it and try to stay away from the exhaust manifold. So, Where i am sitting right now is I had a clogged cat (pass side) and ended up with a shorting out plug wire after! I went through codes yesterday individually and my EGR was fine. Do you have any codes? INJECTORS.. You would have to pull the entire upper intake and individually volt check each injector. I never did it but tried to avoid it!

08-14-2011, 11:37 PM	#12
thegirlin48127 Wannabe Elite Explorer wyandotte, Mi. 97 explorer Join Date: Jul 2011 Posts: 10 Vehicle Specs (Original Poster)	I am sea foaming it, changing the wires, replacing the throttle body gasket (I took it apart the other day and found it was bad; the on that goes directly on the intake from the throttle body) and I'll clean the cat converters like you said; removing the O2 sensors before sea foaming it...I don't need any problems with them getting clogged/dirty as well, as they are not cheap @ $50 ea. x 4.... give it a new air filter and hope that'll take care of it... how did it go with yours? have you fixed the issue? ..I know u said you located a faulty wire but I was just wondering if you replaced it and fixed the issue or if I have to keep looking .... I tried taking the wires off of mine but I was taking them off if the coil one at a time till I got zapped ..lol... so I reconsidered my approach ... do you think it would have been a better idea to take them off of the plugs instead? it's just the exaust manifold is right there so I figured it would've been easier to take them off of the coil.... besides burns seem to hurt longer than just getting zapped for a second .... I really appreciate all the feedback lil'mounty...thanks for all the tips

08-15-2011, 08:39 AM	#13
budwich Wannabe Elite Explorer Ottawa, Ont 96 XL Join Date: May 2005 Posts: 3,246 Vehicle Specs	First, you should get your fuel pressure tested to see if it is running within spec. Next,IF you think you have a cat problem. Disconnect them and replace with an equivalent length of straight pipe and make a test run to see if things change ... its a cheap and dirty test. IF they tested and found "misfiring", they should have indicated what cylinders were misfiring. IF it wasn't a particular cylinder, then it is unlikely to be a wiring problem, more than likely a fueling issue (air/fuel mixture) OR timing issue (crankshaft sensor and related "stuff").

08-15-2011, 09:42 AM	#14
lil'mounty Wannabe Elite Explorer Cold Wisconsin '97 Mercury Mountaineer Join Date: Mar 2010 Posts: 18 Vehicle Specs	Yes, I am all fixed! My issue was a clogged cat. The second issue (which I created while doing the cat) was the 'stock' route for the plug wire, started arcing against the rear firewall. Originally, I had your exact issue W/O a code (ever), seafoamed it and cleaned the cats. It is a good idea to check your fuel pressure BUT I will bet you have a clogged cat. You will not get a code for that and it is just as important as air IN. If you do check your fuel pressure it should be 32-40 psi. It does take 3 good cycles w/ the key to get the fuel rail up to the spec 32-40 from 0. (It charges like 12 psi a 2 second cycle) but once there it should hold it in that range, running or off or sitting for 30 min. It's just the initial startup after total pressure discharge. You can drive around without your exhaust (or o2 sensors) to find a hill to try and mimmick the lagging, but I couldn't because laws are kind of strict about that around here.

08-15-2011, 09:38 PM	#15
thegirlin48127 Wannabe Elite Explorer wyandotte, Mi. 97 explorer Join Date: Jul 2011 Posts: 10 Vehicle Specs (Original Poster)	I think you just solved my issue too... I looked under there today trying to get the cats off and I see an area where the carbon build up was coming out (because of sea foaming it a bit) it wasn't coming out of the tail pipes so I looked further up the line and saw where it was exiting (on a coupling from a previous issue) ... I'll let you know how it goes tomorrow (I'll be replacing the wires too just to be sure so I hopefully won't have to work on it in the winter time) .... Thanks again for your help

08-17-2011, 11:25 AM	#16
lil'mounty Wannabe Elite Explorer Cold Wisconsin '97 Mercury Mountaineer Join Date: Mar 2010 Posts: 18 Vehicle Specs	Good! The pipes are a real puzzle to get out/in. It helps to remove the t.case skid plate. If your hands aren't small enough the o2 sensor plugs can be accessed through the inside of the vehicle under the center counsel (there is agood write up on this forum somewhere on pulling the center out.. super easy!). I am sure you'll figure it out. Let me know the results.

08-17-2011, 11:58 AM	#17
rjcooperss396 Wannabe Elite Explorer Fontana, CA '95 XLT Join Date: Jan 2005 Posts: 362 Vehicle Specs	Have you guys done a compression test yet? I recently helped my nephew track down a misfire on his '93 F150 and he had 10psi on cylinder 8. A leak down test pointed to an issue with the exhaust valve and this is what I found when I pulled the head.

08-18-2011, 12:37 PM	#18
lil'mounty Wannabe Elite Explorer Cold Wisconsin '97 Mercury Mountaineer Join Date: Mar 2010 Posts: 18 Vehicle Specs	That would not be cool! In looking at the pic, it makes me wonder how it happened. It looks as if the valve hit the pressure gauge. The reason I say that is if it were run for any period of time there would be carbon on the valve seat and valve break area. It's spotless. The plug threads look very shallow compared to some heads. I hate to tell you this but I think you created extra work for yourself. That' just my opinion, but if that is the case don't worry it happens to us all at some point.

08-18-2011, 12:58 PM	#19
rjcooperss396 Wannabe Elite Explorer Fontana, CA '95 XLT Join Date: Jan 2005 Posts: 362 Vehicle Specs	The threaded part of the compression gauge doesn't enter the chamber. My guess is that it burnt the valve and the valve cracked and broke. This is very common in the 302.

08-18-2011, 01:27 PM	#20
lil'mounty Wannabe Elite Explorer Cold Wisconsin '97 Mercury Mountaineer Join Date: Mar 2010 Posts: 18 Vehicle Specs	Makes sense! I wasn't sure how long the gauge was. Another thing is on our gt40 heads, there are issues w/ 302 plug listings at the parts store. I have noticed some list for plugs w/ longer threading. I believe they assume all 302's have the same heads. I don't know what head that is and I don't think that was the case (or all exhaust valves would have cracked) I just thought it would be worth mentioning.