Could SHOnut FPR cure low RPM studdering & bogging?

[F-22 Raptor SHO]

Gosh. I can't believe what a riddle this has turned out to be. Someone else mentioned timing on this thread. I'm leaning away from that because it just seems that I'd be having more serious problems than sluggishness under 4k and an occasional intake backfire. I reserve the strong possibility that I'm wrong but I'd be utterly shocked if that's what ends up being the problem.

Have you checked your fuel injectors? I imagine that's a pain. I don't even know how to do it. This really seems like a fuel thing to me. I was sure the pump would do it.

Crap... I'm soooooooo sick of this nagging problem. I've put up with it for years...

PLEASE keep me posted on your progress or lack thereof. :type:

Took a break this afternoon and went out on a date with the Misses. Took the car for a spin after reassembly. It ran like I was towing a boat. Gonna attack it again tomorrow. Will have to rename myself to Tenacious SHO....I'm going after the timing next. Here is why:

1: Its easy to check
2: Its easy enough to fix (easier than cutting a hole for a fuel pump and alot less nerve racking.

You will have answers...just not quickly. Gonna check the spout connectors (or lack thereof) as well before I tear into it.

I have a coolant leak that has been getting worse lately. It may have been enough to cause a timing belt to slip? A check of the timing will tell.

 

[hawkeye18]

you know, I just thought of something. Might apply, might not. My wife's car had a stumbling problem for the longest damn time. It felt like it was missing at idle, and it got worse as it got warmer. I thought it was the IAC. nope. It wasn't the spark plugs/wires, DIS, coil pack, fuel pump, fuel filter, injectors, FPR, A/C clutch or idler pulleys either. I just about damn near gave up when one day I was putzing around the battery area and noticed that that one wire from the computer that goes to the battery neg. terminal had just one strand left on it and was almost completely broken. I figure, "hmm, that can't be good," and since she has a blue-top with the 5/16" studs on there I clipped the ground wire, put a ring terminal on there and put it on the stud with a lockwasher and a wingnut.

The car runs like a champ now. It was the computer ground the whole damn time. So what I suggest is to take a REAL close look at that ground wire. Make sure it's WELL connected to the battery terminal, with no rust or corrosion. Also, check the connector about 6" up from that, and also where it screws into the body on the strut tower. Remove, wirebrush, reinstall. Spray contact cleaner into the connector. Also, check the big strap at the back of the intake on the pass. side. I left that off once on my car after a wire job and the car barely ran at all and it would stall out constantly.

Check your grounds people!

 

[morebhp]

Micael, I'll blindly throw this out: Knock sensor?

 

[F-22 Raptor SHO]

Micael, I'll blindly throw this out: Knock sensor?

A bad knock sensor would throw a code. But considering it affects timing, I see your point. I will be replacing it when I do the Fuel Injectors (which are my last resort).

UPDATE: I did check the timing (well, the position of the cams relative to the 0 position on the crank. Timing is dead nuts on. SPOUT connector is in place. I will pull it out and put it back in to make sure the contact is good. I will also pull the connector on the BARO sensor to see if the car runs differently.

While checking the timing, I took the opportunity to replace my cam seal in the rear as it was leaking. I will put everthing back together and check the two things above. If those are not the issue I have the injectors and the plug wires as my last hope. I say last hope because the wires are only 22,000 miles old and the injectors are ...well alot of work and expensive.

 

[morebhp]

Okay. I'll stand by for the results. This is incredible.

Someone else suggested perhaps the ECU itself were the cause. I tend to doubt that too. But... as you narrow the field of possibilities... I'm loosing faith in any sort of logic.

What's your gut feeling? Does it feel like misfires due to a lean mixture or due to mistimed or missing spark?

Also (just grasping at straws here) is there any way to dynamically test manifold vacuum pressure during real-world operation? I keep returning to the thought that it's some sort of vacuum leak. But... from where... that's the question...

I wish I could be more help....

 

[F-22 Raptor SHO]

you know, I just thought of something. Might apply, might not. My wife's car had a stumbling problem for the longest damn time. It felt like it was missing at idle, and it got worse as it got warmer. I thought it was the IAC. nope. It wasn't the spark plugs/wires, DIS, coil pack, fuel pump, fuel filter, injectors, FPR, A/C clutch or idler pulleys either. I just about damn near gave up when one day I was putzing around the battery area and noticed that that one wire from the computer that goes to the battery neg. terminal had just one strand left on it and was almost completely broken. I figure, "hmm, that can't be good," and since she has a blue-top with the 5/16" studs on there I clipped the ground wire, put a ring terminal on there and put it on the stud with a lockwasher and a wingnut.

The car runs like a champ now. It was the computer ground the whole damn time. So what I suggest is to take a REAL close look at that ground wire. Make sure it's WELL connected to the battery terminal, with no rust or corrosion. Also, check the connector about 6" up from that, and also where it screws into the body on the strut tower. Remove, wirebrush, reinstall. Spray contact cleaner into the connector. Also, check the big strap at the back of the intake on the pass. side. I left that off once on my car after a wire job and the car barely ran at all and it would stall out constantly.

Check your grounds people!

checked. I also added another engine ground to make sure the ground was good.

 

[morebhp]

I tried driving a day with my MAP disconnected. Didn't make much difference. If anything, I'd say it took a little away from the power above 4K.

I reconnected it on the way home from work. I just got more and more ****** as I drove. The car is a freaking dog. I've done about all I know to do and have read countless threads on this issue. I've about had it. I may as well get something requiring less maintenance if my SHO is going to drive like a SLO. What's the point.

Throttle tip-in at 2K results in a short bump like its actually going to accelerate and then it feels like someone dialed back the timing. It leasurely runs up to 4K at which point the car lunges forward. I've had shorting wires, this is not that feeling. The engine is just not making power.

I've run codes over and over. Nothing.

You guys just may be seeing a '95 MTX with 63K miles in MINT condition on the for sale page soon. I've put up with this for probably about 9-10 years. Enough is enough.

Micheal, you're my last hope. I'm 40 now and getting to old for this crap. If you give up... that's my sign.

 

[F-22 Raptor SHO]

I tried driving a day with my MAP disconnected. Didn't make much difference. If anything, I'd say it took a little away from the power above 4K.

I reconnected it on the way home from work. I just got more and more ****** as I drove. The car is a freaking dog. I've done about all I know to do and have read countless threads on this issue. I've about had it. I may as well get something requiring less maintenance if my SHO is going to drive like a SLO. What's the point.

Throttle tip-in at 2K results in a short bump like its actually going to accelerate and then it feels like someone dialed back the timing. It leasurely runs up to 4K at which point the car lunges forward. I've had shorting wires, this is not that feeling. The engine is just not making power.

I've run codes over and over. Nothing.

You guys just may be seeing a '95 MTX with 63K miles in MINT condition on the for sale page soon. I've put up with this for probably about 9-10 years. Enough is enough.

Micheal, you're my last hope. I'm 40 now and getting to old for this crap. If you give up... that's my sign.

Oh **** no. I'm not giving up. You arent either (At least if I have anything to help you not quit) I just came in from my re assembly. Oh and I'm 40 in november

Another overall summary:

MAF, no

ECT, no

ACT, no

Fuel Filter, no

Fuel pump, no

air filter, no

plugs, no

intake vaccum leak: not that I can tell, and I've had it off alot.

timing: no, dead nuts on

spout connector: no

BARO sensor (sometimes called a MAP):...disconnected and its tough to tell....will know more in the morning. Seemed to help

DIS: well I swapped in another one and the problem seems lessened, but I would say no.

Next: and last hope: plug wires (mine are looking good, but have 30k on them. Resistance of the plug wires is 7,000 ohms (least the front 3 are), which is better than the 16,000 ohms of the oldies i have in my cabinet.

and the injectors....many think they are bad.



I think your problem might be different than mine actually as you have alot of backfires. I'm going to throw out what I think your issue is: go check the plugs on your coil pack right now...er, well when you want to: the order of the plugs is as follows:

 

[morebhp]

I must have given the wrong impression. I get a small backfire on average about once every 2-3 months. I may have said once a month. I guess it varies. It happens typically within 5 minutes of startup and after a long (3-4 minute) period of idle... like at a long light. It's quite rare and never happens while under load.

My coil pack was replaced about 2 months ago. --I had a bad one and was causing a miss. I THOUGHT that was the extent of my problem. It was only one of the many layers I've worked through.

I'm confident my wires are good. I've changed them twice in the last few years trying to solve this. Never does. My dad takes my hand-me-downs for his '91 and never has a problem with them.

I guess I could try replacing my plugs... again... but... I'm just so weary of it all. I've been through a lot of plugs... and still the problem remains.

I can't imagine there's any severe wear on my cams or shims with only 63K miles and religious oil changes. Like I said, I've had this problem for years and that's back when I had <20K miles. I don't even drive it that hard. --No reason to. It's slow. But I digress...

 

[F-22 Raptor SHO]

Dont keep doing the same thing expecting a different result as that can only lead to insanity. New plugs wont help. Are are the wires put on the coil pack correctly? Many times 5 and 6 get switched and the error is carried on the next time.

BARO unplugged does no good. Still misses and ****** when cold and doesnt pull much when warm. DIS swap with another one I had in a box didnt do good either.

Wires this week, Injectors this weekend.

Im wondering if I stressed a wire somewhere when I did my motor mounts. I had the engine quite high and didnt unplug anything. Will also check the Coil to DIS pathways.

 

[morebhp]

Good point. I guess I want to remove them from the pool of possible suspects. They can crap out on you so suddenly. Mine are probably two years old (about 15K miles) but... for the money and time involved, I may just do it Saturday so I can stop wondering.

My wires are right. I've checked that a couple of times.

Today it was running a tad better. Sometimes it momentarily felt like it had some balls and then at other times, flat as a pancake.

Mileage is decent. I'm averaging around 20 in town.

I don't have the luxury of two SHO's to swap parts on. That's really helpful. You are able to try things that I just can't.

So injectors are about the only thing left aye? It almost has to be them. What else is left? The cup holder?

 

[SHO-NUF93]

Just a simple suggestion, but try a fuel additive specifically designed for removing moisture from the fuel system. The probability of it not helping for a problem that's been there for a decade is questionable, but ~ $7 is not much lost...moisture floats on fuel, condenses on the top of the tank, etc, so it's possible it may never fully remove itself.

If you guys are gonna go replacing things, try the alternator also. I've seen them cause issues before... this may be an option for Raptor, since he has his wife's to swap & test from...not to say it may fix one and not the other, or vice versa.

And before replacing injectors, I would attempt a true fuel injection cleaning. Where they connect a special fitting to your fuel rail and run the car off of a can of really good stuff for about 30 minutes. Cleans the injectors, ports, and upper combustion chamber.

 

[F-22 Raptor SHO]

fuel additive tried. Burning off all the remaining gas from that tank. Then off to shell for some good stuff.

cost of cleaning is about the cost of the injectors I have access too.

Both cup holders replaced. No dice.

oh and now I have the flu or food poisoning hence all of my during the day posts

 

[morebhp]

I hope you are feeling better soon.

There's one more thing I wanted to mention and see if you experience the same thing as I do regarding this stuttering problem.

In the morning while the car is still cool just after starting, I notice that for the first 60 seconds or so, my throttle response is VASTLY better than it is at all other times. I'm not sure what this indicates if anything but I've noticed this hundreds of times. It's a constant.

These are the three run "conditions" I experience:

(a) For ~60 seconds immediately after startup. Good throttle response, no stuttering.

(b) First 5 minutes after startup. Moderate to severe stuttering during part-throttle acceleration. (This is the only time it may [once a month] give a small intake backfire and only after a protracted idle and I again touch the throttle to go.)

(c) Regular operating temperature. Stuttering under part throttle lessens but remains. Feels like ******** timing until 4K rev point.

Bottom line: There is some condition immediately after startup that prevents the horrible throttle response and stuttering. But what?? It's for this reason I contend this problem involves the electronic engine management system because it doesn't always do it. --If it were a static mechanical problem, it would be there under every circumstance.

Make any sense?

 

[F-22 Raptor SHO]

feeling a bit better. Havent eaten much.

I replaced the plug wires just to be certain I didnt stretch one of them. Ran a compression check while I was in there. compression values were consistent 135 to 165 (note: I am 7,000 feet above sea level).

Car seemed spunkier I think, but time will tell (in the morning). Have learned a bit from Tom on how the BARO sensor operates. It sends a signal at start up and that is it. So if my sensor is misreading (say atmospheric instead of 7k in the air), then the car would run poorly whether it was plugged in or not. Will test that theory in phx tomorrow if it runs poorly in the am.

 

[morebhp]

Glad you are back among the living. Those stomach things can be debilitating.

I replaced my plugs with Autolite XPs. Now i have a slightly smoother idle but I still have my low rpm sputtering. I'm back to suspecting fuel pressure. My plugs were a little light in color. If I recall that indicates lean mixture. I'm going to post a pick of them later today. I also finally bot a fuel pressure gauge last night. I'll hook that up this afternoon after my kids soccer games.

I really hope the pressure is low. At least that would finally be some clue.

 

[F-22 Raptor SHO]

Here is a question: What kind of plug wires did you use?

I put on a set of taylor 8mm SpiroPro's....jumped in the car this morning and it ran ok. Drove it 259 miles (to PHX and back). Didnt have any problems.

 

[morebhp]

I have A/C Delco wires... about 3 years old. I put them in hoping they'd solve the very problem I'm still having.

Thursday I put in Autolite XPs. The ones recommended by many on the forum. Check out my recent post requesting plug color analysis.

 

[F-22 Raptor SHO]

I saw your bad # 4 plug. That could be all kinds of things. Leaky ring, leaky valve seal, bad injector, bad plug, bad plug wire.

I think we are zeroing in on your problem which I think are the cheapy plug wires you are using. A/C Delcos are better suited for GM. I just put a set of Taylor 8mm spiro pro's from Summit Racing on the car. Why Taylor? well the motorcrafts are 150 bucks now. Taylors are widely used and are pretty good. Seemed to have helped my situation. I can still feel a bit of it I think, but its worlds better than it was.

 

[morebhp]

Hmm. I don't know. That would be my 4th set of wires on this car trying to chase this problem. I think I may look into the injector possibility. If I put another $100 into wires and had no improvment again I just may give up. I've already spent so much screwing around with this thing.

I'll give it some consideration though.

What about the coloration of my plugs? That white color on the side electrode... looks peculiar.