New 5.0L built, low compression and horrible MPG

[beach]

This has been going on so long and you've done to many things to check, imo your only option is to have a "reputable" shop check it out. I mean its been 7 months. Should have taken that other shop to small claims after what they did.

 

[1997XLTRollover]

This has been going on so long and you've done to many things to check, imo your only option is to have a "reputable" shop check it out. I mean its been 7 months. Should have taken that other shop to small claims after what they did.

Well the truck was off the road for 6 months I'm kind of now just picking it back up. I don't have the money to bring it to a shop to charge me a couple hundred dollars to tell me to just change a bunch of stuff. I want to do my due diligence before I bring it anywhere.


How about a bad spout connector or one that's missing? Anyone have any idea how many there are and how to test them? BTW I know OBD2 shouldn't have one, but I found what looks just like on near my coil packs so is that one or is that something else?

 

[koda2000]

This is what you said about your compression when you started this thread...

"I only tested 3 cylinders, 2 on the passenger bank and 1 on the drivers and all 3 read 125-130 psi cold and 130-135 warm without adding oil to the cylinder. This to me seems pretty low, could my machine shop have screwed up the hone job and my engine isn't broken in right? Or am I freaking out for nothing? I feel like the thing should have more power than it does and have at least a 160 psi cylinder pressure."

124-130 PSI IS LOW COMPRESSION, and you haven't even tested all the cylinders. Lack of on-going break-in should not make that much of a difference. As you said yourself, you should have between 160-165 PSI in all cylinders. You shouldn't have to add oil to achieve that. Adding oil is just a way to verify a ring issue rather than a valve issue. There has been no (and there will be no) simple solution to an engine with low compression. Your gas mileage sucks because your engine is running inefficiently.

I agree with beach, you need to take your truck to a qualified trustworthy mechanic and/or take the shop that did the work to court. The money you spend having the problem diagnosed you can get back in court.

 

[1997XLTRollover]

This is what you said about your compression when you started this thread...

"I only tested 3 cylinders, 2 on the passenger bank and 1 on the drivers and all 3 read 125-130 psi cold and 130-135 warm without adding oil to the cylinder. This to me seems pretty low, could my machine shop have screwed up the hone job and my engine isn't broken in right? Or am I freaking out for nothing? I feel like the thing should have more power than it does and have at least a 160 psi cylinder pressure."

124-130 PSI IS LOW COMPRESSION, and you haven't even tested all the cylinders. Lack of on-going break-in should not make that much of a difference. As you said yourself, you should have between 160-165 PSI in all cylinders. You shouldn't have to add oil to achieve that. Adding oil is just a way to verify a ring issue rather than a valve issue. There has been no (and there will be no) simple solution to an engine with low compression. Your gas mileage sucks because your engine is running inefficiently.

I agree with beach, you need to take your truck to a qualified trustworthy mechanic and/or take the shop that did the work to court. The money you spend having the problem diagnosed you can get back in court.

I think it's somewhere in the thread but I have since then tested all 8 and all 8 test at 135 perfectly even not even 134 on one and 136 on another. They're perfect at 135 across the board. I've had a few guys say they have compression numbers at 135-140 and that my compression is not too far off base. My cylinders may be higher now as it's breaking in even because I tested it a while ago. But my question to you then is, if this is in fact a compression issue and my 99 was also 135-140, why did it get 17/20 mpg and my 96 can only pull off 10/13?

 

[koda2000]

I think it's somewhere in the thread but I have since then tested all 8 and all 8 test at 135 perfectly even not even 134 on one and 136 on another. They're perfect at 135 across the board. I've had a few guys say they have compression numbers at 135-140 and that my compression is not too far off base. My cylinders may be higher now as it's breaking in even because I tested it a while ago. But my question to you then is, if this is in fact a compression issue and my 99 was also 135-140, why did it get 17/20 mpg and my 96 can only pull off 10/13?

Question: Are you testing your compression with the throttle body held in the open position?

 

[1997XLTRollover]

Question: Are you testing your compression with the throttle body held in the open position?

It's been a while but I want to say yes I did it with it open.

 

[Dono]

I'm still with Koda, the compression is low.
I'm certain if you check the shop manuals, they will tell you that its out of range.

Maybe you have another issue also, but the compression is an issue.


edit: ok, im finding conflicting info also.
http://forums.mustangworks.com/f8/compression-test-47147/
geez.

 

[1997XLTRollover]

I'm still with Koda, the compression is low.
I'm certain if you check the shop manuals, they will tell you that its out of range.

Maybe you have another issue also, but the compression is an issue.


edit: ok, im finding conflicting info also.
http://forums.mustangworks.com/f8/compression-test-47147/
geez.

Exactly what I'm finding, so I'm ignoring ALL of it. Look at it how I am. My 99 which has GT40P heads so has a hair higher compression stock reads 135-140 (depends on the cylinder but after all she does have 160k). My 96 reads dead on 135 on all cylinders and has GT40 heads (but had heads milled just to true them up so it's probably close to the 99 heads chamber size). So my 96 having 135 and my 99 having 135-140 seems like both trucks are just fine.

Now! Let's assume the compression is low on both trucks (my 99 ran incredible but that's besides the point). If the 99 has low compression as well, please explain to me how the 99 with 135-140 can get 17-20 MPG after 160k miles and the 96 with the same compression can only pull 10-13 with only 2k miles on it. I Just don't buy it.

I've also had other guys with solid running trucks tell me they also have 135-140 for compression. Maybe the guys with higher compression have excessive carbon buildup or something I have no idea.


Oh and to be fair both trucks had stock tires, and both trucks have awd with 3.73's. Now I know the 99 has a plastic fan and the 96 is metal, but the 96 has Torque Monster headers on it so that should really make up for any loss for the fan vs the plastic one on the 99. Oh and my fan does spin freely it's not locked up in any way.

 

[1997XLTRollover]

Ok guys so I bought a smoke machine with UV dye. I've been wanting one for years and decided to bite the bullet. My findings were interesting to say the least. The one leak doesn't surprise me and is actually exactly where I guessed I may have had an intake leak. The other 2 are a bit weird. I may have more but this was all I could see. When I pull this all apart again I'm going to replace all my vacuum lines under the intake just to be safe.

Leak 1: Intake manifold gasket.

It actually hissed when I ran the smoke machine through it, so it must be pretty bad. I also have a small coolant leak here (why I expected an air leak too), so the intake or head must not be flat or the gasket is junk. I'm going to get Felpro gaskets and maybe put some rtv on them too and hope that does the trick.

Leak 2: IAC around the seams of the metal cap (not the gasket)

I'm going to clean this up and slop some RTV over it around all the seams. IAC works fine so I just have to seal the small leak and I'm thinking some copper high temp RTV should work just fine.

Leak 3: EGR

Now this one was a bit weird. I couldn't pinpoint it but it looks like it's coming right out from the center of the EGR on the back of the intake. Could my EGR valve be cracked or is it normal for this valve to leak intake air when not under vacuum?

 

[Dono]

1. lower intake to block....
At that spot, throw away those foam pieces and use a good thick bead of rtv on both ends before re-installing. All I've ever heard from everyone is not to use those pieces. I have not had a problem at that spot with using an rtv bead that I'm aware of.
2. the iac valve....normal.
If you take the iac apart, you will actually see a vent at the spot where its blowing out.
3. egr...normal. There's actually vent holes all the way around the egr. Interesting, but true. [MENTION=61294]vroomzoomboom[/MENTION] just lived the same experience.

 

[1997XLTRollover]

1. lower intake to block....
At that spot, throw away those foam pieces and use a good thick bead of rtv on both ends before re-installing. All I've ever hears from everyone is not to use those pieces. I have not had a problem at that spot with using an rtv bead that I'm aware of.
2. the iac valve....normal.
If you take the iac apart, you will actually see a vent at the spot where its blowing out.
3. egr...normal. There's actually vent holes all the way around the egr. Interesting, but true. [MENTION=61294]vroomzoomboom[/MENTION] just lived the same experience.

1) I used the rubber gaskets and put RTV on, are you saying ditch the gaskets completely and use only rtv?

2) So I shouldn't seal this? Leave it alone?

3) I had a feeling this was the case but wanted to be sure.


I just can't believe this little intake gasket leak can cause 10mpg yet the truck still runs ok. If the truck was stumbling and running horrible I could see that, but it's running ok. Either way it's certainly a problem so I'll start there and see where it gets me. This baby coolant leak has been annoying me anyway. Just sucks because it's my only vehicle at the moment so hopefully I can get this fixed in a day.

 

[Dono]

1) yes, next time just ditch the 2 end gaskets (Front and back of motor). Keep he two that go on the head.
2) yup, leave it alone
3)

I really kinda doubt its a vac leak causing that ****ty of mileage. That would have to be one super massive leak. I wish I could be more helpful. I really don't know what to say.

 

[1997XLTRollover]

1) yes, next time just ditch the 2 end gaskets (Front and back of motor). Keep he two that go on the head.
2) yup, leave it alone
3)

I really kinda doubt its a vac leak causing that ****ty of mileage. That would have to be one super massive leak. I wish I could be more helpful. I really don't know what to say.

Yeah I doubt it too, especially because I don't even have lean codes or bad running. Either way it's a problem. 1 step at a time. My suspension vibration with this thing has been a combination of multiple things too. This engine issue might be multiple problems too.

 

[Turdle]

Wondering if the toast engine in the 96 clogged the cats

 

[1997XLTRollover]

Wondering if the toast engine in the 96 clogged the cats

I wondered the same thing, but I ran the truck and shot my temp gauge at my cats and both were 4-500 degrees which is pretty normal I believe.

EDIT: Could they still be clogged up even if they aren't overheating?

 

[Turdle]

I wondered the same thing, but I ran the truck and shot my temp gauge at my cats and both were 4-500 degrees which is pretty normal I believe.

EDIT: Could they still be clogged up even if they aren't overheating?

I thought cats ran way hotter than that.

via ask . com


The normal operating temperature of a catalytic converter is between 550 and 1,600 degrees Fahrenheit with the optimum temperature being about 806 degrees.

Also
I am not sure if temperature and flow are related or not. I think you really need to go to an exhaust shop and have them test the back pressure to know if they are clogged.

 

[1997XLTRollover]

I thought cats ran way hotter than that.

via ask . com


The normal operating temperature of a catalytic converter is between 550 and 1,600 degrees Fahrenheit with the optimum temperature being about 806 degrees.

Also
I am not sure if temperature and flow are related or not. I think you really need to go to an exhaust shop and have them test the back pressure to know if they are clogged.

Well I only drove maybe 5 miles before checking them, my truck also seems to be running really lean which could effect the cat warm up due to lack of fuel. Maybe I should check them after a long trip. I might just replace the damn pipe, I've been welding holes up in the rotting piece of junk for a while now. This truck has turned into a huge money pit. I wish I scrapped it before I did the engine. Should have kept my 99. It was in such better shape and never gave me any problems on top of having a super lift and clearing 35x12.50's.


Oh and I did look down the pipe when I had it off the truck and the cat I could see looked fine, nor did I hear any rattles.

 

[1997XLTRollover]

Here's one of my spark plugs after 2k miles.

 

[Turdle]

Which one is that?

That looks like it's brand new-dead injector- bad connection to injector?

 

[koda2000]

I though I'd responded to your spark plug condition pics earlier, but I don't see it now. Your spark plugs indicate you are running WAY lean. They should not be bright white after 2000 miles. A normal plug running with the correct air/fuel ratio should be a tan color. There is something seriously wrong.