Hey guys -

First off, please don't flame me, I've been searching for an hour, and am a little closer, but still am pretty clueless on what's wrong.

First off, the car is an 89 T/A 5.0 TPI w/ T5 tranny. For a while, it was having problems when under a lot of load (ie starting from a stop, or applying throttle after shifting), it would kind of studder a little bit, but otherwise would run fine at WOT, or under light load.

Well, it eventually got bad enough where I couldn't give it any throttle at all or it would try to die. I managed to get it home by riding the mess out of the clutch, and slowly getting it up to speed. When I got it home, I checked the codes, and it gave me a 22 (low voltage at the TPS). So, I replaced the TPS, and it did the same thing.

Limped it back to the shop, and adjusted the TPS properly, still did the same thing. So, I noticed the wires going into the plug were slightly frayed, so I replaced the plug, wired it in, and still the same. But, it quit throwing codes.

I got tired of messing with it and let it sit for a few days with the battery unplugged, and came back to it, and it seemed to run fine! I thought it was wierd, so I took it for a test drive, and didn't even get one mile from the shop before it started acting up in the same way.

So, I checked the fuel pressure, and it was reading right at 40 with the vacuum line to the FPR off, and around 30 with the vacuum line on. I know that it's supposed to be 43 with the line off, could that be the problem? Or maybe the regulator?

The only other thing I'm worried about is a short in the wiring harness somewhere, because it just acts like it's not picking up the TPS.

Any suggestions? Thanks guys...

 

don't know for sure but I have the same year/combo and the same problem but not as severe. My next step was to check fuel pressure under load to make sure the pump isn't weak, but that was 2 years ago and I sorta forgot about it and parked the car.

 

Test the circut right back to the computer. Wiggle the harness a few times and retest. If you can have someone else do the wiggling while you hold the meter on the terminals will help a lot.

If that fails then try a scan tool and see what the TPS is reporting back. Could be the PCM or a faulty new TPS.

 

Sounds like it could be a misfire from your discription. Sure all 8 are hitting? Did you check the voltage levels in your wires?

 

timing maybe?

 

Well, it does the same thing whether driving or sitting there revving it, so I haven't checked it while driving.

Haven't thought of this, but it idles and runs pretty smoothly until you try to give it any more than about 1/4 throttle.

Hmmm, another thing I haven't checked yet...

Thanks for all the suggestions so far guys! Keep em coming, and I'll have plenty to do over the weekend...

 

Have you tried unplugging the battery again long enough for it to clear the ECM of any codes?

If that makes it go back to normal then that's a heck of a lot better direction to go.

 

Yeah, I've done that a couple times, and it seems to go back to normal for a few minutes, but as soon as I take it out and drive it, it goes back to doing the same thing. Also, it quit throwing codes when checking with the self-diagnostic paper-clip in the plug method.

 

It has to be a computer monitored unit then. I could go through a list of sensors, but there's only so many that are active when the car's still cold. Have you checked the EGR?

 

fuel filter? heard similar problems, Egr valve could be leaking... i had that problem... idles okay..? but cant rev it up?

 

New fuel filter, but exactly, idles ok, and I can rev it up if I don't give it over about 1/8-1/4 throttle. Is there any specific way to check the EGR, or do I need to take it off and put a vacuum pump on it?

 

Its not the egr, thats the opposite. Idles like dog crap but runs fine under load.

Check the fuel pressure with the engine under load and make sure its not dropping off.

Next most likely thing could be the MAF. If its under reporting the flow then the engine will go lean under high loads.

Another possibility is a weak ignition system. If the spark is weak then the engine will misfire under load. Lots of causes for this. Spark plugs have too large a gap. Module is on its way out, faulty coil, low voltage, etc...

 

Take a look at this post. (Somebody get me a Doctor!!! 11/06/04) I have what sounds like the same issue. I have also spent countless hours putting my head through a wall over it. I'm now looking into the fuel pump for a third time. It's the only thing that is left. I'm also thinking of starting a support group for guys like you and me!!

I like this web site alot, don't get me wrong, but it seems that there are alot of self proclaimed experts with not alot of experience attempting to answer posts with out reading the whole post. Just my opinion!!!

 

Is your car blowing any type of smoke at start up or when you try to give it gas? Try checking your plugs.

 

Dont know about everyone else here, but Im no expert. I have, however, owned alot of crappy cars that always liked to break down, so Ive gotten more then my fair share of experience from fixing their problems.

To the origional poster,

The first thing Id check is the fuel pressure under load, just to get it out of the way. If there is steady/rising pressure when the engine is under load, then you can cross the pump, filter, and all that related stuff off your list.

The next thing Id look at is the MAF. Ideally youll need a scantool to check it. Rev the engine up and note the reported MAF flow. Sort of hard to say exactly but the reading should rapidly rise up to something like 60-100 grams/sec. If it stays low or only reports somehting like 15 grams/sec then your going to need another MAF. Id almost say check the injectors but the fact that the car still idles ok means that theyre probably ok and delivering the proper ammount of fuel.

Id next look at the ignition system. The most obvious thing to check is the spark plugs and wires. Stupid stuff but it can cause major issues. Make sure the wires are in good condition. If in doubt, replace. Check the gap of the spark plugs. If theyve worn alot and the gap has opened way up, then the engine will crater under any sort of load. Dont forget to check the terminals in dist. cap as well as the rotor. Anything that causes a weak spark will produce bogging/stumbling under load. Other sources of ignition problems will be harder to check. Coil/Module are the two most obvious things. The only way to really test them is by substitution with a known good part.

I had some serious problems with my ignition system like two glowing header primaries from damaged wires, intermitent spark loss, lack of power, tach going crazy (bad module), etc. I ended up stripping the distributer down to nothing and ripped out everything ignition related and replaced it all. Rather draconian approach but it fixed my ignition problems.

 

OK, but the thing is, I can get it to bog just sitting there revving, it, with no load. At first, it was only under load, but now it does it all the time whenever I try to give it over 1/8-1/4 throttle. I couldn't even drive it back in the shop Friday because I couldn't give it enough gas to rev up...

As far as the ignition system goes, the plugs, wires, distributor cap, and rotor are all under 1 year old. The coil is about 6 months old.

The MAF was replaced about 1.5 years ago, but that could definetly be it. It's a Bosch, and ever since I put that one on there, it has run rich.

So, I guess I should try a module first, since they're not too expensive.

It does smoke when it cranks up, due to bad valve seals, it's done this ever since I've owned the car.

 

OK, wanted to give you guys an update. I started thinking about what a few of you said pertaining to ignition troubles, and I had recently replaced the plugs, wires, cap, rotor, and coil, but not the ignition module. Put a new module in it today, and it seems to be running fine! Drove it around for about 30 minutes, and couldn't get it to mess up at all!

So thanks for the help guys! Now, I need to tackle the leaking intake gasket...

 

I have the same problem .Was that the electronic control module that you replaced. I to have replaced the wires.plugs,fuel filter,air filter,breather filter,pvc valve and fuel pump six mths. ago

 

No, it was the ignition module that is inside the distributor underneath the cap and rotor. Took about 10-15 minutes to replace it...

Good luck!