blackfrontier

iTrader: (1)

Hello, I have just started to have a very minor "stumble" feeling as I go over my daily mountain pass to work and want to know what to look for before it gets worse. Where is the fuel filter on a TPI? It's a minor "fast stumble" that happens and it's very subtile for now but....... Any tips?

blackfrontier

iTrader: (1)

Okay no response? I had the fuel filter replaced and the fuel pump pressure tested and it checked out fine at 37 PSI. Driving back home from work and the car ran much better up the pass, as I had the cruise control on, but I could still feel that slight "stumble" although maybe not as bad. Its only happens once I get 3/4 the way up at a 3,000 foot summit. I have today off so any other suggestions besides checking plugs and wires? It would seem like if it was plugs or wires it would not just stumble near the top of a mountain pass.

evilemokid94

iTrader: (6)

Bump for you, this seems interesting

Untamed Z

If it only does it when you're climbing up this mountain, I would say the thinner air up there is causing it to stumble. All cars will perform better at sea level as opposed to running at elevation. If it runs good everywhere else, the thinner air is the problem. Just my .02

Vader

Transitioning from 2,200' to 3,000' AMSL means the barometer drops from about 13.5 PSIA to about 13.2 PSIA. Your '87 should be equipped with a MAF so the measurement of intake air would be reasonably accurate despite altitude changes.

The problem may be that the timing curve is based on TPS, RPM, and the resultant calculated load (LV8), and those load calculations start to grow larger error margins at about 1,800' AMSL. The timing may be jumping from one setting in the tables to another at a hair-splitting level of TPS and RPM. If your TPS closed throttle voltage is correct you MIGHT have one of the rare situations where bumping the TPS voltage toward the top end of the adjustment range (about 0.60VDC) may band-aid the symptoms.

Further, if the ECM is going open-loop for any reason during your climbout, the default mixture (injector PW) is likely too rich for the actual conditions. You can check the ECM mode while driving by jumpering the ALDL and watching the blink rate of the SES lamp.

blackfrontier

iTrader: (1)

I'd like to get this figured out for sure. When I had a 160 degree thermostat in everything was fine driving over the pass. Since my mileage sucked I went with a 180 and that has been fine until a couple of days ago this started up. Seems the hotter it is the more noticeable but the issue still exists to a lesser degree when cooler. On the way to work it was cooler out and I ran at 180 all the way up and could barely notice the stumbling and on the way back at 93 degrees outside and car running at 210 or so it was more noticeable. Also noticed on a secondary grade it stumbled subtly a couple times. Since the car "was" fine before with either thermostat I don't know what could make that condition suddenly start to happen. Is there something I should be checking? Car runs perfect otherwise.

blackfrontier

iTrader: (1)

So what would cause this condition, how can I diagnose it properly and what part(s) would be faulty?

waltersb

Why don't you start by switching back to the old thermostat and see if it cures it. If that's the change you made and it just started happening.

blackfrontier

iTrader: (1)

The car was running fine with the 180 thermostat. In fact it feels like it is even starting to stumble now on lower grade hills.

blackfrontier

iTrader: (1)

Feels like gas or maybe ignition problem but not temp related. I need some ideas to check out

Mishimoto

When's the last time you did plugs and wires?

blackfrontier

iTrader: (1)

Well I have only owned this car since this January and have not replaced the plugs or wires. I heard this was owned by a mechanic before me and the wires, o2 sensors, and air filter was clean. I looked at the ignition wires and they seem fresh but I'm not sure there couldn't be a problem with them. I just don't have the funds to replace stuff if it won't fix the problem, and a lot of people replace plugs, wires, cap and rotor and still have the same issue. If it was a plug or wire issue wouldn't the car run this way all the time?, and not just when on a steep incline? Fuel pressure seems normal during a steep grade climb according to the gauge and I have a new filter. Can anyone make an argument that would lead me to believe wires and plugs could be bad only under an uphill load?

Mishimoto

I've seen misfires due to ignition components become more pronouced under an uphill load than regular cruising. Those vehicles were OBII and I was able to verify the misfire by driving while watching a power balance and seeing which cylinder(s) would drop. On my early 90's V8 (non-OBDII) I'd notice a slight misfire while climbing the mountain that leads out of my town. It normally would take a few weeks (depending on how many miles I put on the vehicle) before the misfire would be present during all driving. Have had some instances when plug wires are touching/rubbing each other and under heavy load cause slight misfire.

It is cheap to remove the plugs and check them for problems. It is also cheap to look under the hood with the engine running while it's dark out and look for arcing off the plug wires. I'd do those two things first seeing as you want to not just throw money at the car. Have you run it in the rain lately?

waltersb

My last truck would bog down and shake under load and > 3/4s throttle... but it was fine reving in nuetral. Never did find the problem, but a mechanic said it was likely an ignition starvation issue.

blackfrontier

iTrader: (1)

So far it has been sunny and dry out. No raining at all. I might just go ahead and do the plugs and wires. The car was purchased last January so I have no idea when they were done last. Wires look to be in newer condition but I know that can be deceiving too. I might start with removing plugs and see how they look. Is there a condition of the plug that would make a car do this?

waltersb

Check for gap. I think you want .04? or something and for it to be consistant on all 8 plugs and look for gummy plugs. You should see clear white ash on the node. (I think... it's been awhile)

Mishimoto

Reason I asked, on my 90's V8s some wet weather would turn the slight misfire(from plug wires) into "am I going to make it up this hill?".

Check the gap on the plugs, and just make sure they look like they are burning good. Last summer put brand new plugs in my car, and the insulator tip actually lost a chunk in 300 miles causing some funky things

blackfrontier

iTrader: (1)

Well on this TPI 350 I cannot even get my big hands down to the spark plugs. I can barely get a spark plug socket on there and I have yet to figure out how to get a wrench on it with all those fuel lines in the way. After 20 minutes I have yet to even figure out how to get the most eccessable plug out (drivers side front), let alone any of the other ones. My second gen T/A is way easier. Do these get pulled out from the bottom or what??

blackfrontier

iTrader: (1)

I pulled the distributor cap and rotor and they look brand new as does the ignition wires. I have notice the stumble is starting to be evident on lesser grades, particularly after driven on the highway for 30 minutes. I wonder if the fuel pump could be struggling even though it was pressure tested? Maybe under load it could be faltering?

evilemokid94

iTrader: (6)

either go in through the bottom or pull the engine up.

blackfrontier

iTrader: (1)

UPDATE***** I found the plug, wires cap and rotor are fine. My mechanic said it could be a faulty fuel injector or an intermittent fuel pump problem. His suggestion was to start with pulling injectors and have them cleaned and inspected first, then if that doesn't solve it look at a fuel pump. What do u guys think?

Mishimoto

I think he's on the right track. Going through the systems piece by piece will eventually turn up the issue. Who knows, he may find a wire somewhere that is grounding out causing the problem, 25 year old cars can have strange surprises

grygost

Do you mean it's "surging?" If it's surging that's a lean condition. If the plugs look like ashy white or any white at all you are leaning out. Throttle position is steady constant and then when you open it up or start to hit the throttle thats where more air is being introduced and the stumble is the gas trying to catch up. Hardly happened with carbs as they had the "squirters" that threw more gas in as the throttle opened but TPI depends on the computer as well as any EFI. When the car is cold your A/F ratio is rich until it is at operating temp; then the Computer and sensors kick in and try to keep you at a 11:1 I believe I could be wrong on that figure. 160 thermo is because the engine was cooler thus running slightly richer.

blackfrontier

iTrader: (1)

Well I replaced the fuel pump and on the way home from work the throttle felt more responsive and is an improvement but it still stumbled or "surged" rapidly as I climbed the pass. I'll see how it does on the way to work today. May be electronic related. The plugs looks good and clean like new. Wires looked new but will have to check for arching. My issue is I never seem to get a day off to explore it. I'd have thought the dealership would have checked that anyway but is there a sensor that could be faulty that could do this? I ran seafoam through the tank as well as techroline on the second tank. Not sure if I should replace injectors but I'd rather check first for anything electronic.

mmadden55

Jump your diagnostic adl and see what codes if any have set. My guess is your cat is clogging up probably because your o2 sensor is out.

blackfrontier

iTrader: (1)

I good guess but the converter was replaced a few months ago and the O2 sensor was replaced before I bought the car in January as its nice and shiny new looking.

blackfrontier

iTrader: (1)

BTW there were no codes stored either. This has to be a faulty injector or something electronic. Maybe I missed a bad plug wire but the plugs and wires are new too

TTOP350

iTrader: (8)

Is the converter locking or unlocking at this point in the drive for some reason?
Do you have a K&N ? if so, has the MAF wire been cleaned with spray cleaner lately??

armos

Bad ignition often causes problems going uphill. Also, you mentioned earlier it might be getting worse with higher temperatures. If so, that sounds more like ignition to me than injectors. A fuel injector problem can be heat related, but I'd expect that more often with ignition. Uphill and hot is a very likely time for ignition to misbehave.
I wonder about the ignition coil or the ignition control module. ICM failures are definitely heat sensitive, I don't know if there's a good way to test them though. Parts stores test ICMs but since this isn't an all-out failure I wouldn't have much confidence in them finding the hiccup.

Does your tachometer drop out? If it drops below the actual engine speed it would imply a problem on the ignition side. It might be hard to see this unless the stumble is prolonged though.

Another possibility might be the MAF sensor. I've seen that on 2 Thunderbirds with failing MAF sensors, both were misfiring uphill, worse with heavy throttle. It will run lean if the MAF is going bad.

blackfrontier

iTrader: (1)

Thought about trying to clean the MAF. I have never done anything with it. The air filter is stock and is clean. The car doesnt run hot. In the early morning it's even cool out and going up the pass and other foot hills it runs 170-180 all the way. When it stumbles its quick and I don't notice the tack drop at all. I can step on the gas and accelerate still even but that stumble becomes faster and more pronounced as well. After almost 40 minutes of driving or more I can notice a more subtle stumble even on a flat surface at 70-75 mPH the limit out here.

TTOP350

iTrader: (8)

I'd mount a remote fuel PSI guage and watch that while the car stumbles..

blackfrontier

iTrader: (1)

That was a good idea and many have suggested it. I noticed on the way home from work driving over the pass the tach didn't really respond to the constant stumble up the mountain. With a new fuel pump, filter and several tanks with seafoam or other cleaning agents in the tank I'm still not sure if it's an injector issue or something else.

blackfrontier

iTrader: (1)

With good plugs, wires, cap and rotor, and injectors that check out (at least in the car), would cleaning the MAF make any difference? What else could cause this issue?

TTOP350

iTrader: (8)

If your car has a K&N filter its good to clean the maf wire everynow and then because the motor sucks the oil off the filter and it covers the wire (even with the burnoff feature).

blackfrontier

iTrader: (1)

I don't have a K&N filter. The stock filter looks pretty clean still. I doubt that would cause an issue. I notice after a 40 minute freeway drive, and cruise in town the idle can seem to bounce around some. My car has a digital dash so I don't really see much in the way of RPM fluctuation as the idle "stumble" is a quick pulse. I would guess its related the the high speed stumble? This one is really challenging. Even the mechanic notes from the dealership state plugs and wires are good, fuel injectors are at spec as is fuel pressure. I suppose replacing them would be a good idea but I just spent plenty on the fuel pump and that didn't fix the problem and money to blow I don't have.

blackfrontier

iTrader: (1)

The latest update is the idle can be inconsistent and have a miss or stumble. Even on some even roads (not going uphill) acceleration has that stumble now and even when the car is cold. I really want to look at anything that could cause that. Any sensors? Idle sensor or TPS? MAF?

TTOP350

iTrader: (8)

You need to check Fuel PSI while driving and ohm the injs, if you haven't yet.

If it was mine, I'd put in a new GM pickup coil, ICM, cap, rotor and plug wires also.
I do it for all my cars every few years or several thousand miles just for piece of mind.

Have you OHM'd the injs yet?

blackfrontier

iTrader: (1)

I will figure out a way to do that and check it out. I'd have thought a new fuel pump would make the pressure correct though.

blackfrontier

iTrader: (1)

Well here is an update after more repairs. I have checked the fuel pressure with a gauge while driving and there is no issue there. I just replaced the fuel injectors with the Bosch series, new TPS, new battery and cables and a new MAF burn off relay. The car runs better although I haven't gone up a mountain pass because of snow. The plugs and wires were checked by the service center that did all this work (including the fuel filter and pump last summer) and the plugs are fine. The car starts and idles great like always and has smooth acceleration and shifts well when getting on the freeway but when you mash the gas pedal it seems to lag power and not take off and downshift as hard as it did, and also at hight speed acceleration has that sort of mild stumble and bumble. I'm now thinking weak torque coverter ? I also noticed a code 33or 36 so could a bad MAF or computer do this? Car engine runs beautiful but seems to not be able to get the power to the wheels like it used to. I'm getting unnerved so please help! Lol

blackfrontier

iTrader: (1)

*****I took the car to a transmission expert and it is not the torque converter nor the transmission. At light steady throttle the car gently "wallows" through the entire RPM range and he pulled the ECM code for MAF. I spoke with some auto techs that would indicate I should replace it. Reading on the success (or lack there of) on aftermarket MAF sensors has me wondering which is best? I will also check for vacuums leaks and functioning EGR. Nobody has chimed in with advise but I figured you may want to know how I'm progressing.

blackfrontier

iTrader: (1)

UPDATE*****
It has taken until now to get this figured out. After replacing fuel injectors, fump, sensors, and plugs it seems the lower intake manifold gasket had a minor leak. We suspect a vacume leak from it. I took it to the dealership I work at to have it replaced. I checked on it during the process and made sure the intake runners and TPI were cleaned of carbon and a new EGR valve installed too. car was buttoned up and took for a test drive and now the throttle is smooth and car doesnt stumble, but acceleration is FLAT! At cruising speed I floor it to pass a car and it sounds like I'm "busting a move" but the car doesnt move. I have left the car overnight and the tech who worked on it will double check the spark plug wires to make sure he didnt get a couple of them mixed up but anyone else have any ideas? I have already ruled out torque converter.

blackfrontier

iTrader: (1)

So the tech reset the timing and the car took off and barked off the.tires like she used to, but heading up the dang mountain pass and the car stumbles or surges again! The acceleration is not smooth. I'm at a loss. Not sure what else to check at this.point. Bad ecm?

rdhanded2

iTrader: (3)

Ecm, timing, coolant temp sensor.

blackfrontier

iTrader: (1)

Funny but I was just thinking about trying the temp coolant sensor next and then ecm if that doesnt do it.

blackfrontier

iTrader: (1)

okay new temp.sensor and the car idles and runs great until you step on it or drive up a mountain pass under load and it still does the stumble. I am wondering if wiring the electric fan to the fuel pump wire under the hood is causing this issue? At one point I got tired of burned out toggle switches for the two fans so I had somebody wire the left fan to come on with the key, which turned out to be the wife to the fuel pump. Could there be some voltage issue under load? I really cannot remember having the stumble issue before this was done, but I have replaced everything just short of the ECM?

InfernalVortex

iTrader: (4)

DId you ever check into the ICM? Ive never actually seen plug wires fix anything, but I've seen ICM's fix all kinds of problems.

blackfrontier

iTrader: (1)

I always figured a bad ignition control module would make the.car not start at all. The only things not replaced would be IAC, ICM, ECM, coil, pickup coil, and knock sensor. Not sure what would cause this to stumble under load or heavy accelleration. RECAP: replaced TPS, EGR, coolant temp sensor, plugs, wires, cap/rotor, intake gasket, fuel injectors, fuel pump/filter and related relays as well as MAF.. My shop did the intake gasket and said the the manifold pressure switch might be faulty, but I guess he should have suggested that when the intake was off! If I do the ICM I would put a new coil in as well. I had a Fiero once that had a weak coil and the computer tried to over compensate by dumping more fuel in. my car seems to have a vacume or spark related issue under load as fuel pressure was tested with a gauge while heading up a pass and was steady. vacume lines were replaced too, so unless there is a hidden vacume line somwhere? Would having that fan wired to the fuel pump wire cause an interruption?

InfernalVortex

iTrader: (4)

Im not saying it's your problem, but in my case I had an intermittent misfire for months. It got more consistent and would hit between 4500-6000 RPM. I changed the coil and it started doing it at 2300+ RPM. Just big misses and stumbles. Replaced the module and it went away. That module failed a year later, but it started giving me random misfires before it failed. They can fail in all sorts of strange ways. They can fail and never work again. They can fail when hot. They can be intermittent under load, all sorts of things.

Like I said, not saying it's your problem, but dont be so quick to rule it out.

blackfrontier

iTrader: (1)

I think I might just by a new coil and ICM and give it a try.

blackfrontier

iTrader: (1)

UPDATE***** I bought a new ICM , IAC and Ignition Coil and during instalation the distributor was determined to be bad. it was corroded inside and the wire connectors dissintigrated when trying to install the ICM. I went and bought a whole new distributor and had it put in. The car seemed to run well but chugged even more going over the fourth of july pass. It seemed to be making better spark and inflamed the symptoms I have been having. I wonder if I should just put all new plugs and wires? They have been checked but I have run out of things to replace less the computer. Suggestions?