the_wolf222

To make a long story short the car runs great until I press down past about 3/4 throttle. When I do, the car goes into a limp mode of sorts where it gets stuck at about 3000 RPM and doesn’t accelerate. I’ve replaced the fuel filter, MAF sensor, TPS, spark plugs, cap and rotor, ignition coil, intake temperature sensor, and added a cold air intake but none of these have helped. I’ve tried cleaning out the injectors with Seafoam and Lucas injector cleaner but to avail. The only code I get is a lean code on both O2 sensors. Any suggestions would be greatly appreciated!


Attached is a video of the car doing it. The video was taken while the car was in park; however the issue happens when in drive also. The first rev is me flooring it then immediately letting off, second is me flooring it then slowly letting off. Notice the cars RPM rises in the second rev once I start letting off. (It wouldn’t let me upload the attachment so here’s an Imgur link https://imgur.com/gallery/T1H7FLj)

wbrockstar

It almost appears as if the ECU is commanding the factory rev limiter at 3000-4000rpm.The ECU commands the limiter at 6250rpm.
Take the air intake hose off the throttle body then floor the pedal & lay a block on the pedal to keep it floored then look inside the throttle body and verify if the throttle blade is opened fully.If not,I have seen several cases where there was slack between the pedal arm & the cable end and zipties were placed on the cable at this location to take out the slack.Look at the image below where the yellow zipties are located.Now look at your pedal.Is slack present on the cable at that location?? If yes,get a few zipties,grab the cable end & pull it towards the rear of the car.Wrap zipties around the cable until the slack is taken up.
Now floor the pedal again and verify if its opening fully now.If it is,reinstall the air intake hose and retest its revving ability now.If this wasnt the issue,disconnect the harness from the maf sensor and retry the revving test.If it does better,theres an issue with the maf sensor or its wiring.If it doesn't run better,
reconnect the harness and move to the next test below.

Test voltage at the tps with a meter to verify the tps & wiring are intact.You can run a needle through each tps wire to touch your meter leads to or backprobe the tps harness plug for these tests.
1) With the key on,touch the red meter lead to the brown/white wire & the black meter lead to the black/white wire.The meter should read 4.0-6.0 volts.If yes,the vref wire is good.
2) With the key on,touch the red lead to the gray wire & the black lead to the black/white wire.The meter should read between .50 - 1.19 volts.If yes,gradually open the throttle fully then close it fully.Voltage should increase/decrease smoothly with no spikes or sudden drops.
3) WOT voltage range should be:
Closed throttle voltage + 2.71v= min wot volt So if your closed throttle voltage is .80v,your minimum wot voltage should be .80 + 2.71v Minimum to Maximum WOT Range would =
3.51 - 5.0 volts
If the tps passes,I'd test fuel pressure at the Schrader valve.
Key On/Engine Off = 35-45psi
Key On/Engine On = 30-40psi

the_wolf222

Thank you very much! The throttle body does open all the way; that was one of the first things I looked at. I have also tested fuel pressure but only when the car is idling. I've read on other threads to try and test what happens with the pressure as I press down on the throttle, would that be a good idea? I'll check the voltages as soon as I can find my multimeter and I'll report back.

wbrockstar

Yeah do that.As you rev the engine and vacuum drops,pressure should increase slightly due to vacuum dropping at the fpr vacuum hose.When vacuum is present there,like during at idle,its easier for fuel pressure to unseat the diaphragm/valve returning excess fuel to the tank,but when vacuum is removed,it requires more pressure to unseat the valve,so pressure increases slightly.You can try doing a bleeddown test also.Test pressure with key on/engine off,turn the key off,wait 60 seconds then record pressure again after 60 seconds with the key still off.If pressure drops more than 5psi in that 60 second period,the check valve in the pump is bad or the fpr or an injector is leaking.If your test results do like described above,I'll post another test you can do to verify whether its the pump or one of the other two parts that are bad.Do you ever experience long crank times or needing to cycle the key on/off 4 or 5 times before cranking to get it to start?? If you didn't do that quick harness test disconnect check for the maf sensor,make sure you do.Faulty parts come off the shelf constantly at local parts stores,if thats where you bought the maf from.Ive also seen a tfi cause a similar issue,but it would cutout between two rpm points but run normal below & above those points,so its not likely the cause.Pump or maf sounds most likely.

the_wolf222

Voltages coming off the TPS seem fine. My wires were different colors from what you noted but I figured that out. Weird thing with the MAF test, I unplugged it and it revved all the way up, so then I plugged it back in and it still worked fine (issue was gone). Then I drove it down the street and it was doing it again. After parking I tried revving it again and it once again kept getting stuck. Very occasionally the car runs perfect, but we can’t figure out the situation in which it does. At this point I’m pretty close to just bringing it to my family mechanic and having him spend a day looking it over but if there’s a way I can do it myself that’s what I’d prefer lmao. It does take a little while to start some times but It’s never been what I would think is cause for concern. I need to pick up a new fuel pressure gauge before I can test the pressure because mines missing some pieces, but I checked it a few months ago and it seemed to be fine at least when the pump primes.

TrimDrip

the capacitor in the ecm that deals with the maf is going bad maybe?

or the maf itself

the_wolf222

MAF was replaced recently, thank you though. Honestly I’m starting to think the ecm might be going bad.

TrimDrip

when you unplug the maf, the computer switches to a failed maf table. That is probably why the engine was able to rev with the maf unplugged.

the_wolf222

If I unplug the MAF and drive it it still does it though. Stalls out like crazy, but still won’t rev all the way haha


I’m not sure why it revved fine that one time because I’ve tried unplugging the MAF before with no change at all

wbrockstar

Your symptoms seem like an intermittent maf problem or pip sensor problem & since you replaced the maf sensor already,the pip sensor being defective is a high probability.
However you should notice some type of change in how the engine runs when disconnecting the maf sensor,if nothing is wrong with it.
Sometimes when the pip sensor begins to act up,symptoms will sometimes begin once the engine reaches operating temp or after its been at operating temp for a short amount of time.It also wouldn't hurt to remove the cap & rotor then remove the two screws that holds the distributors shutter wheel on and lift it off the shaft to see if the tabs are dirty with rust/grease/oil or if one is bent or has contact marks on it from hitting the pip sensor magnet.If any tab shows evidence of the things listed directly above,it will cause your issues.These tabs pass by the pip sensor magnet to indicate cylinder firing order.The pip sensor works like a crank position sensor and its also used to trigger injector pulse.So your pip sensor may be faulty and/or the condition mentioned above about the tabs could also cause your issues. You also need to check your spout plug to make sure its still plugged in because the ecu wont advance timing if the spout is removed.If you decide to replace the distributor vs trying to hassle with replacing the pip sensor,Rich Porter is supposed to be the better brand of the parts store dizzys and seem to hold up better.Sometimes when the pip is bad,the timing marks on the balancer wont appear or they'll be bouncing around alot with the spout plug in & a timing light on the balancer.The tfi module has also been known to cause the lack of revving issue too,but not as often.You can bring it in and have it tested to rule it out or test it yourself with a meter.Heat it up with a blow dryer before testing it,if you're gonna attempt testing it at your house & if you have the parts store employee test it,tell him to run it numerous times so the machine will heat it up accordingly.