Engine misfire

[drbadbyte]

hi, i have a '96 explorer xlt that seems to have an engine misfire problem. i have changed spark plugs (motorcraft), spark plug wires (motorcraft) and coil (brand not known, but bought at Ford). that didn't help at all.

often (not always) when i start the engine it doesn't run smooth for a few seconds (3-5 sec), like it runs on 5 cylinders. after 3-5 sec it normalize but the rpm stabalize at aprox 1000rpm (a bit to high i think). when i go back at my car and listen to the exhaust it's like a wobbeling sound, like it skips a cylinder now and then, but you can't hear or feel that from inside the car.

when i take it for a ride, and drive at 60km/h in 4th gear, and around 80km/h in 5th gear, and steps slightly on the pedal to increase speed, it can (not always but very very often) start to misfire. at least that's what i feels like. almost the same feeling you get when you run out of gas. the car shifts to 4th gear around 60km/h and 5th gear around 80km/h. when i drive at 2nd or 3rd gear uphill, the rpm tends to fluctuate (goes up and down a few rpm). today i discovered that i have lost some coolant fluid, way below refill point.

yesterday i drove the car to a mechanic (50 min drive) to check the car. ofcourse the car behaved nice and the obd scanner showed no error codes. took it for a ride with the mechanic and nothing happend. he had the car overnight to test drive it more but still nothing happend. i picked up the car today and after aprox 40 min drive it started to misfire again. whith an our price for the mechanic of around $200 i don't wanna go back..hehe..norway is a very expensive country. bring your own beer if you ever wanna go there

some guy told me today that it might be a crack between the intake valve and the exhaust valve that might be the problem, but shouldn't the problem occour all the time then? could it be that one of the valves turns while driving and at one position it closes entirely and at another point it doesn't, like a broken or burned valve? could it be a fuel problem, like clogged fuelfilter?

it would be much easier if the problem was there all the time and not come and go...

this is what i can come up with at the moment. any suggestion are appreciated. just ask me questions and i'll try to answer.

btw, no engine light comes on when this happens!!!

 

[firepop5]

Bad gas?


Deteriorated air filter?


Vacuum leaks?

 

[drbadbyte]

"bad gass?"
- don't think so. i ran two gass tanks with this liquid you blend with the gass to get rid of water. and i've also tried the "new" shell v-power gass.

"Deteriorated air filter?"
- i've changed the original air filter with a K&N filter. you never now, but i don't think that's the problem.

"Vacuum leaks?"
- it has touched my mind. when i push the throttle to a certain point i can hear a weak and tiny kind of a vacume sound. it whistles a bit, bearly hearable but it's there.

at the moment i'm monitoring the coolant fluid to see if there's a leak. there's no spill on the ground, and my oil is black so what i'm thinking is that there might be a leak in the gasket between the engine block and the top (not sure what you call it).

thanks for showing some interrests to this frustraiting problem i have...everything seems fine, but it's not...grmpf

 

[duke16]

After it's been driven a little, how does it idle?

 

[manaen]

Check fuel pressure, and fuel filter, you could have a bad injector. Are there any codes for the miss to tell you which cylinder it is? You could run a odb misfire test to see if it is isolated to one cylinder.

 

[drbadbyte]

After it's been driven a little, how does it idle?

It stabilizes at aprox 900-1000rpm. I've read some place on the forum that it should be around 500rpm?

 

[manaen]

the idle should be at about 750rpm
Is this an SOHC? if it is, you may be suffereing from the common intake leak that causes rough idle. The fix is a set of upgraded (thicker) oring gaskets for the upper and lower intake. Ford had an upgrade to fix this and some other issues, I think it is 00m12

with your added description I'm leaning more toward vacuum leak

 

[wyochimneysweep]

map sensor contimont from the oil from the kn filter. clean your maf

 

[manaen]

Yeah that ^^^ is a good possibility too

 

[boboz1]

Cam sensor?
Or does cam sensor only affect idle?
my 2000 5.0 misses when I am at idle sometimes but mine gave a code which I forgot at the moment but the engine light goes off sooner or later. I know my code was a cam sensor malfunction.

I don't know if that will help but I just thought I throw my situation out and maybe it might help the process of elimination.

 

[drbadbyte]

the idle should be at about 750rpm
Is this an SOHC? if it is, you may be suffereing from the common intake leak that causes rough idle. The fix is a set of upgraded (thicker) oring gaskets for the upper and lower intake. Ford had an upgrade to fix this and some other issues, I think it is 00m12

with your added description I'm leaning more toward vacuum leak

it's a 4.0L 6 cylinder OHV, i'm not sure if it applies to this engine but i'll check it out and maybe just do the change to see what happens.

 

[drbadbyte]

Check fuel pressure, and fuel filter, you could have a bad injector. Are there any codes for the miss to tell you which cylinder it is? You could run a odb misfire test to see if it is isolated to one cylinder.

The fuel pressure and fuel filter have crossed my mind, but I haven't thought about the injector. If I have a faulty injector, will there be any codes for that, because when I plug in an OBDII scanner, it returns no error codes and that is ofcourse very frustrating. I bought autotap a while a go but I'm returning it tomorrow (20. june) because it's not working...ofcourse. I will use it as soon as get a new one to see which cylinder misfires. Meanwhile I'll do a compression test on all the cylinders to see if there's a leak.

 

[manaen]

When you remove the plugs be sure to "read" each plug as you remove it and note any indications of a problem.

 

[drbadbyte]

ok, i've been reading some more threads in this wonderful forum
to me, seens i don't get any codes or engine light, it looks like it's something "mechanical" that's broken.

#1. engine idle at aprox 900-1000rpm (when engine hot)
- i've cleaned the IAC so don't think that's the problem, but because of the problem described at #4 the IAC can't compensate enough to keep the idle at 750rpm??

#2. when starting the engine, it can now and then misfire for 3-5 sec before it runs "normal".
- i've checked the MAF sensor for correct voltage, seems ok. can probably malfunction due to dirt etc that the PCM doesn't register. i've also heard that when you do a cold start of the engine, "all" the sensors runs on preprogramed values untill the engine starts gaining some temperature??? i was thinking of maybe the MAF runs on a preprogrammed value from the PCM when cold, but should the engine misfire on startup then??? i'm just speaking my thoughts here folks

#3. when the engine has reached its work temperatur it can again, now and then, starts to misfire. because of that, i was thinking that the MAF sensor might be broken.

#4. i've been trying to narrow it down, and after reading this thread http://www.explorerforum.com/forums/showthread.php?t=217303&highlight=maf+sensor i hope it's a broken upper manifold gasket. i think the engine gets som "false" air through the broken gasket. what do you guys/girls think of that?
it shouldn't be that hard to change the upper manifold gasket, but if i have to change the lower gasket...hmm...maybe someone else should do that.

#5. at last i have the fuel system to check. it could be a clogged fuel filter? maybe the injector is broken? should i try to measure the fuel pressure? i have a fuel pressure gauge but to be honest, i don't know how i connect it to the fuel system. anyone knows of a thread that describes the process?

any thoughts are very much appreciated, and thanks for all the comments so far

 

[BAStumm]

I had the exact same problem. Replace the intake manifold gasket, when it leaks it allows coolant into the cylinders. This causes the misfire. On a cool day you might notice the car steams for a few minutes after start up out the exhaust (looks like white smoke). As it gets worse it will set codes for random multiple misfire plus identify a couple cylinders missing, for me it was 3 and 4 (front driver side and rear passenger side). Ford now sells an upgraded gasket that is better than the original. Common problem on these vehicles. The reason for missing on cold start is that after parking the radiator is pressurized and it leaks off the pressure into the cylinders through teh leaking gasket. Thus on startup there is more moisture than under running conditions. This also explains why your coolant level is getting low. Important to note that the coolant doesn't leak into the engine oil. Also replace your spark plugs after/when doing the gasket. The coolant destroys the plugs and the inner electrode will eventually fall off inside the engine. Happened to me, I didn't replace the plugs when I did the gasket...

 

[drbadbyte]

I had the exact same problem. Replace the intake manifold gasket, when it leaks it allows coolant into the cylinders. This causes the misfire. On a cool day you might notice the car steams for a few minutes after start up out the exhaust (looks like white smoke). As it gets worse it will set codes for random multiple misfire plus identify a couple cylinders missing, for me it was 3 and 4 (front driver side and rear passenger side). Ford now sells an upgraded gasket that is better than the original. Common problem on these vehicles. The reason for missing on cold start is that after parking the radiator is pressurized and it leaks off the pressure into the cylinders through teh leaking gasket. Thus on startup there is more moisture than under running conditions. This also explains why your coolant level is getting low. Important to note that the coolant doesn't leak into the engine oil. Also replace your spark plugs after/when doing the gasket. The coolant destroys the plugs and the inner electrode will eventually fall off inside the engine. Happened to me, I didn't replace the plugs when I did the gasket...

thank you for your reply. finally someone who apparently have experianced the same problem that i have. i really hope it's the gasket so i can fix this once and for all. thanks for the tip regarding changing the spark plugs after the gasket change.

 

[tvalentino]

how hard would it b to change the gasket? and is it the lower gasket?

 

[drbadbyte]

how hard would it b to change the gasket? and is it the lower gasket?

as far as i can see in the manual, it's much easier to change the upper gasket. i am changing the upper gasket

 

[BAStumm]

Normally I would have done the work myself and I dont believe its that hard of a job but it probably is the majority of a weekend but when I experienced this I paid a shop to do the work because I was too busy at the time. It cost me about USD500. In all I paid the shop 700 but I had some other work done at the same time.

EDIT: This is the lower gasket...

 

[ballin]

Hi,

I am having a similar problem, and have noticed some coolant loss.
I often get a misfire on startup, and also when the engine is slightly laboured at around 1500rpm it misfires badly.
IE. when i join a dual carriageway, and travel at about 80km/h revs are around 1500rpm and the car misses quite badly, so i have to either back off, or floor it to drop a gear and then the misfire goes.

This inlet manifold gasket, obviously both side will need doing, but I dont understand what people mean by the lower gasket? I haven't actually looked, but I would have though the inlet manifold just has one gasket, and one inlet manifold for the left and one for the right bank?

I know I should look before posting but I am at work