Unique misfire problem
 

UPDATE: here is the video

Hello everyone,


I just found this forum because I am so desperate to figure out what is wrong with my 2001 v6 MT.(175k miles)

So here is the story.

Once the weather got better here in Southwest Virginia my mustang started to sputter/jerk/jump/misfire when pushing gas pedal more than it is needed. Sudden flooring at 25mph in the 4th gear would cause the engine to misfire, sputter and behave badly. Same situation with all other gears(except 1st): when going slowly and hitting gas the car would jerk, misfire and sputter. Interestingly, same thing happens during idling. If I hit gas hard the engine momentarily kind of vibrates and misfires. If I gradually press the gas pedal it acts very smooth. The idling itself is very smooth. When accelerating with WOT the car misfires and acts weird till about 3500RPM after that it gets better but not perfect. At about 5000rpm I can hear occasional backfire (not sure where from , sounds more like intake). Overall it seems like the car only acts weird when the gas pedal goes(fast) beyond certain level until that level it is totally fine.

First thing I did I changed fuel filter with 0 results and a lot of gasoline spilled around me.


Check engine light is NOT on (!). However once hooked up to the computer it show cylinder 1 misfire. After replacing wires and plugs it does not show any codes whatsoever.

I tried to disconnect&connect DPFE sensor while the engine was running, the result was two codes: cylinder 1 misfire and high voltage in DPFE.After reseting codes nothing came up again.

Having read a lot of stuff on the forums decided to check if new DPFE would do anything. Tried it with 0 results. Then I took off the coil pack and tested it with multimeter. All the resistance values turned out to be consistent. So coil pack is rulled out.

Then I tried to change the EGR valve itself, which kind of helped to reduce the jerk and sputter. Now under sub 3500rpm acceleration car does not jump/sputter/jerk so violently but the gear shifter still vibrates with vengeance. With windows rolled down I can clearly hear the misfire under the above mentioned conditions.

The local shop guys are waving arms saying they have no clue what is going on because the car "ain't throwing no codes". The shop guys rulled out cam sensor , DPFE sensor and fuel pump and even injectors. They said that it can't be cam sensor or injectors because car would not start and idle so well. It can't be fuel pump because at high rpm the car goes really well. It can't be DPFE sensor because it is not throwing any codes.

The big question is what part is responsible for dealing with inappropriately hard pressed gas pedal and why it can't handle too much throttle anymore ?


Guys, you are the only people who can help me here.
Thank you!

Change your fuel filter first. Low rpm load will require the most fuel. Start there and report back.

I forgot to mention that I did fuel filter first.

My '97 3.8 V6 HoopTBird did this. It turned out to be leaky injectors. I replaced them, all done.

It **NEVER** threw a code about it specifically. Only said one side was rich or something, but it kept clearing itself. It was sporadic, and wouldn't throw it when I would actively go out and try to find the problem when it was happening. It was really really odd, I tell ya. I think the Ford 3.8 computers aren't nearly as smart/data capturing as the V8 ones, sometimes...

However, the cats went bad soon after I fixed that problem, so indeed, it was leaking, and badly, on the left side. I wound up replacing all the injectors just to be sure. But the damage was done, all three cats wound up being bad.

Then, of course, a year later, I'd had enough of fixin' all that crap and more and got Awesome. Heh. Almost a waste of the FIs. :p It was a lovely day when the ball joint literally fell out of the lower control arm on a parking lot turn. Thank goodness it was there and not the freeway...

I would therefore ask how they eliminated the fuel injectors, as it was not when it was running. It was when it *wasn't* running that the problem was happening, as they would leak down, and cause the issues. It's likely your cats on that side are destroyed if what I think happened has come to be...

Of course, all that's a major guess, but only because mine did it. It was really weird, I tell you. Freaky weird.

Plugs and wires man. Inspect the coils for any rust or corrosion build up. Eliminate all the obvious first.

Wow that is indeed really weird. You know what, couple months ago I had a light come on saying there is something wrong with bank 2 oxygen sensor. People at Advance Auto said that it could be because the cats are going bad. So what you are suggesting here is very plausible. Thanks a lot!:)


UPDATE: Forgot to mention that my battery light comes on and off all the time. Perhaps that is indicative of something ? As for the injectors I just researched and it seems I don't have any symptoms except the misfire/sputter. The gas mileage is always around 19.5mpg in town and the engine starts fine. Either way, perhaps I should make a video and share with you guys ?

Check the voltage of the throttle position sensor. Should be .997-.999 with the key on and engine off

Thanks for the tip. Are you saying that throttle does not send consistent signal to all cylinders ? Is that even possible ?

The computer calculates how much fuel and timing the engine needs based on throttle position, airflow across the MAF, temperature of the incoming air, and a few others. If one is skewed or not functioning, performance will suffer. When you check the voltage on the TPS, slowly open the throttle with your hand and watch the voltage. It should rise smooth and consistently, up to around 5V. If it jumps, falls, or just plain cuts out, you will have symptoms like you are having

I see. Your reason seem perfectly plausible, and I can't deny the fact that local shop employees had not even mentioned throttle position sensor. Thanks a lot, I will check it and see today.

UPDATE. This guy here ( ) talks about different values and adjustment. Is adjustment a possible culprit ?

Here is the video I shot today:
Please forgive me the shaky quality. I tried my best to capture the sound. I used expensive gear to shoot this video.

UPDATE: It is throwing Cylinder 1 misfire code now. Also, it started to idle little rough. What is it ? Coil pack, dirty injectors ?

The TPS is fine.

That's a good thing really. So you have a coil, wire, plug, injector. Pull the plug and wire. Inspect them. Post a pic of the plug or what else you find. Also post a pic of your coil system, I'm not sure which style you have.

The plugs and wires are literally brand new. By eliminating these two, the only two possibilities are either coil pack or injector. I checked coil pack with multimeter about three days ago and the resistances were all consistent. The only susupicious thing was the excessive resistance in the cylinder 1 wire. it was 4 ohms higher (perhaps because it is longer ?) than the other two cylinders on that side. Unfortunately, changing that wire did literally nothing.

Should I still look at the coil pack or just go ahead and let local shop diagnose injectors ?

I scheduled appointment at one the shops to clean injectors. They want 129$ for the whole job. I think it is a ripoff.

Back to the topic: today I tested the car and noticed that it backfires at high rpms when I tried to go 70mph in the 3rd gear. So anything beyond 4.5k RPM gives mild backfire seemingly from the intake. Does this sound like fuel pump is going out ? Is there a solid way t check weather fuel pump is still good ?

Maybe they should do it for free.

Your sarcasm clearly is substantiated but I have reasons for labeling that price as a ripoff. At first I was quoted 79$, but once I got there in person they added some other fees and it came out 129$. The manner in which they informed about the price is dishonest and does not provoke sympathetic feelings.

http://en.wikipedia.org/wiki/Back-fire#Causes

I am assuming by backfire you are talking about it being in the exhaust. It can be caused by both a leaned out condition, as well as a too rich condition.

The leaned out means the burn couldn't happen in the cylinder... but it does happen, somewhat spontaneously, in the exhaust, when the fuel mixture hits the hot pipes. The richened condition is simply unburnt fuel burning in the hot exhaust pipe.

But given that code you saw, a *leaky* number 1 injector seems likely at this point, to me, given what you've recently described.

I would therefore replace all 6 of them, which are $40 each at an Autozone (I'm sure all the others are similar... but probably not the motorcraft at $80 each I saw online, and probably higher at an actual Ford place, but hey, that's your call. I used them and they were just peachy), so $240 plus tax and some elbow grease (they're not really hard to do... '97 HoopTBird was similar, take off upper intake, swap 'em, put intake back on) and I bet the problem is solved.

It's not that they're dirty. It's that one's leakin'. But if they're gonna hit you with $130 for the cleaning, then just add another $100 and you'll have clean ones all right. :p

thank you for the insight. You convinced me, I am just gonna replace the injectors and see what happens.

does anyone know if it is possible to remove injector of cylinder #1 without removing the upper intake ? I am asking this because the injector in question appears to be quite unrestrained by other stuff around it.