I just bought a 91 Ta. I dont know much about these engine/drivetrain. I just downgraded from a 96 WS6 and learned just about everything about LT1's. Anyway... after the car is fully warmed up for awhile, it seems to run poorly. Here are my symptoms: -At idle, the tach will jump and rpms jump maybe 300rpms -Can only barely touch the throttle, any pedal and it falls off its face -No check engine light The car had the issue before I bought it and the car lot gave me receipt showing work done. Supposedly has new fuel filter, ecm, map sensor, distributor, plugs and wires, intake mani gaskets, and oil pan gasket. It didnt do it until I was on my way home from buying it so apparently the problem is not fixed!! Help please

It's probably having trouble keeping things happy in closed circuit mode. Try disconnecting the MAF or O2 sensor and see if it gets better. It will throw a CEL and revert to open circuit mode. If it does run better, you'll need a scanner to see what sensors are out of line.

Thanks, I'll try that asap. Now what kind of scanner would I use and where would I purchase one?

I just went and looked and I don't see a MAF sensor? Also what kind of scanner would I use and where would I purchase one? Here are a couple photos of the engine bay, just wondering if it looks like anything is out of place as I'm not familiar with these. It looks as if there might be a vaccum line missing off the passenger side of the plenum?

Sorry, your's is a speed density system, no MAF. Just unplug the O2 sensor or the MAP sensor. You can buy a handheld scanner or use a laptop with this: http://www.aldlcable.com/

While I was underneath looking for the O2 sensor (which I never found), I found that the wire to the knock sensor was broken. Fixed the wire and it's all good so far.

Glad it's running better, but the knock sensor shouldn't make any difference.

Well that's the only thing I did, and the car immediately started running perfect afterward. So coincedince or not...

Apparently it was a coincidence. It seems if the car sits for a day or two, then it will be good for maybe 45 min of driving warmed-up. After that it starts acting up. It drove fine until I took a trip out of town today about a 40min drive. I didnt make it back.

Could you tell me where the o2 sensor should be? Cause I didnt see it.

Any help please. Also could it be the TPS or injector(s)? I have a set of 24lb LT1 injectors laying around

The O2 sensor is in the driver's side exhaust manifold. Look down by the steering shaft. Have you checked the fuel pressure when it's acting-up?

I got the car limped home today. It now does it all the time. I can barely touch the pedal or it will just bog down. On the highway it threw a SES for a few minutes. I am thinking it may be the cat converter. I can smell the exhaust once in a while but my girlfriend says it smells like sh*t. Once I got home I pulled the DTC codes, in this order:

32 - EGR system
34 - MAP sensor
44 - Lean exhaust

I havent reset the battery since the purchase, so could one or more of these be a code stored in the past and not be present now? What direction should I head to now? Thanks for any help.

These newer vehicles have engine computers and various electrical sensors all over which input information to the computer.

The best thing you can do is order a factory service manual, learn to use a multimeter, and follow the testing instructions in the manual.

If you can learn to test all these things, then you will easily be able to tell if something is working as it should, then go on to check something else. This can save a LOT of money because you are not "guessing and replacing" anymore.

For example there is a coolant temperature sensor for the engine computer. You can measure the engine temperature, disconnect the wire to this and measure the "resistance" (ohms) to this using a multimeter. Then look in the factory book and see what the value should be at that temperature. If it is reading what it should, then no need to buy a new one!

Same thing with the other sensors.

You can also get a fuel pressure gauge and check the fuel system.

Or get an exhaust pressure gauge and test the exhaust pressure (clogged?)

Basically the factory manual and a few testing tools allow you to "see" what is going on with the various systems and sensors.

Then with a code reader, you can get a specific diagnostic code, and the factory manual will tell you what specific things to test, what the test results should be, and what to test/replace based on those test results.

If you are young, best to learn these things now because a lot more complex systems are in store for the future! Following is a "geeky" book which explains how all these new systems work...

Bosch Automotive Electrics, Automotive Electronics Handbook 5th Edition...
http://www.themotorbookstore.com/9780837615417.html

Then here is a sample of what all can be checked with just the fuel system (Doing things the "right" way)...
http://www.asashop.org/autoinc/june98/techtotech.htm

I got a little time to mess with the car today. First I unhooked the o2 sensor and tried running it and it made no difference. Then I tested the fuel pressure.

With the key on, car off, it is ~42psi and slowly bleeds off. Then idling it is at ~37psi, and when I try to rev it, it will bog down and the pressure spikes up to 45. Also while it was idling I removed the vaccum hose from the FPR and it jumped to ~45.

I would ohm out the injectors. Should be ~ 16 ohms. Under 12ish is toast.

I've seen injectors cause symptoms you describe. Bad injectors pull a lot of current and tend to overheat the injector drivers in the ECM, causing a stumbling until it gets some "rest"

Could you please explain to me how to do that ? Just to be sure

just use a digital multimeter.

Unplug the injector, touch the probes to the two prongs on the injector, and read the resistance. What you are doing is measuring the resistance across the injector coil. As they short out the electricity doesn't have to go through so much wire and the resistance drops.

Thats what I thought but just wanted to make sure. Here's what I found out today.

Cyl -- Ohms
1 - 17.0
3 - 17.0
5 - 12.2
7 - 16.7

2 - 12.3
4 - 3.2
6 - 18.2
8 - 18.2

So, obviously #4 is shot, what about #2 and #5? I have a full set of good #24lb LT1 injectors laying around... would these work just fine as a replacement or will it run too rich?

2 and 5 are getting to be on the low side. Looks like you might have found your problem.

I would put the LT1 injectors in. They are bigger then the stock, but should be better then what you have. The computer should be able to compensate up to a point. It will run rich for sure, but it will run.

If you ask nicely in the DIY prom board, somebody would probably burn you a chip with a new injector constant so you can use the LT1 injectors without running rich at all

I changed out all of the injectors with another set of 19lbs and it's running as good as new. Thanks for the help!

Glad you got it running!


Sooooooo, what are you doing with those LT1 injectors ?

Well they're just sitting around unless someone wants to take them off my hands

depends if the price is right! I'm jonesing after a set for my megasquirt project.

Hey man, I had a similar problem with my 91 350 Tpi. The car ran great and had a lot of power and timing when cold ,yet after it warmed up the car ran rough and just lacked the power it had before. Turns out the car had a hypertech thermomaster chip,which requires a 160 degree thermostat. I would check to see if you have an aftermarket chip in that thing. If you do find out which one by writing down the part numbers and calling the manufacturer. Then check to see if that chip requires a lower temp thermostat. If so, then check to what thermostat you have in that thing now.

Sending you a pm