87350IROC

iTrader: (2)

Hey guys I posted this in the TPI forum a few days ago but it didn't help me find my problem. I'm at wits end with this car, I would appreciate your help.

Here is the other thread
https://www.thirdgen.org/forums/tpi/...ter-water.html

Ok here is the deal. I had some bearing squeal on a 4000 mile water pump. So last weekend I replaced it. At the same time I replaced the coolant gauge sender sensor. The one between cylinders 1&3 in the head. My new heads had bigger sensor holes than stock, so I originally put in the wrong gauge sender. I also replaced the secondary fan switch with a low temp unit.

The install went fine expect now my car runs like crap. At first the car would start bucking/stumbling/hesitating about 3 miles down the road. Over the past week it has gotten worse to the point of bucking/stumbling/hesitating immediately after starting to drive. It will also now hesitate while revving in neutral.

The bucking occurs at any throttle input. If I let off the throttle everything seems to go back to normal. Then if I get back on the throttle, 75% of the time it starts bucking again, 25% of the time it will seem normal, until the next time I get off, then back on the throttle. The above repeats until the car is shut down. The bucking is really fast maybe 3 times a second. If I try full throttle the car falls flat on its face.

Also, the car has a hard start problem that has been getting worse over the last 200 miles. I really don't think its the starter, as the motor spins over fast and clean, it just doesn't start. It takes about 2-3 tries, and it took about 5 tries the last time.

The car is
1987 IROC
350 TPI
EGR disabled in the PROM
EGR is still installed and hooked up, just disabled in the prom
No AIR
24lb injectors
Injectors have less than 2,000 miles on them and check out ok
700R4 trans
Lingenfelter TPI manifold
AS&M runners
ZZ4 cam
Trick Flow 195 heads
headers, cat, catback

What I've tried so far:

1. I am getting no codes.

2. The TPS checks out ok.

3. I unplugged the MAF, it made no difference.

4. I swapped out the ECM with a 'new' one, seemed to help, but not much, as weird as that sounds

5. Base timing is set okay

6. fuel pressure checks out

7. I unplugged the timing advance wire and revved the motor in neutral, it still hesitated

8. I tried a new Ignition Module (EST), it actually made the condition worse, as strange as that sounds, now the car won't hold an rpm in neutral, the rpm will drop, the idle is also now lower

9. I tested the distributor pick up coil using a method found on the forum, it tested ok.
830ohm across the two wires, and infinite resistance between each wire and ground.

10. In the brief time I had a laptop scanning the motor, it looked like the CTS was reporting correctly

I think thats it.

I would really appreciate any ideas you guys have. This car is starting to drive me nuts.

Thanks,

John

87350IROC

iTrader: (2)

Update, I got my original ignition module tested at Autozone. It passed. So now my suspects are:

distributor pick up coil
main ignition coil

I also wanted to mention that when I pulled the distributor cap to get to the ignition module I noticed it had excessive corrosion. I have since replaced it. It only had about 4000miles on it. Anyone know how this can happen?

TMZIrocZ350

How are the wires/plugs? I had a similar issue and I burnt 3 of the wires on the headers. Fire it up at night and see if there is a light show under the hood.

87350IROC

iTrader: (2)

Hey thanks for the suggestion. The wires have about 5 years and 3000 miles on them. The plug wires look and feel nice. None are terribly close to the headers. I do not hear or see any arcing at night. I've burned plug wires in the past, and my current miss doesn't feel the same as a burnt wire.

Also the intermittent nature of the stumbling doesn't point towards bad wires, at least in my mind.

The plugs have about 1000 miles on them. The plugs look ok.

Oh, here is a pic of the distributor cap that I replaced.
http://farm4.static.flickr.com/3017/...448549e3_o.jpg

Keepin This One

A new IAC ,and cleaning the gunk from the t.b,fixed my stumbling problem.
And had no codes.

87350IROC

iTrader: (2)

Thanks for the idea. My IAC is newish, and the passages are clean.

87350IROC

iTrader: (2)

any more ideas for me to check out?

Thanks

ResurrectingZ

When it is running what does the exhause look/smell like? The sensor you are referring to is the one-wire sensor for the gauge and not the CTS you are referring to? Checked the pump to make sure it is circulating (probably not getting hot enough to open thermostat)? Was it running normally before the pump and sensor swap?

87350IROC

iTrader: (2)

The exhaust looks clean/clear. I would say it smells the same as it always has, although I can't say for certain.

As for the sensor, yes I changed the gauge sensor. I did not touch the CTS although I did make sure it is still plugged in.

I have had it up to operating temp, so yes the thermostat did open.

The car ran fine before the swap. The only thing I can think of that I messed with to do the pump install would be the MAF. I unplugged the MAF and the car ran no different. So i'm not so certain I screwed something up during the swap.

I will be with the car this weekend to work on it, I will see about hooking up to a laptop and scanning software.

I'm getting tired of driving 300 miles every weekend to work on the car.

ResurrectingZ

With what your describing how its not pulling codes even after unplugging the MAF that your problem may be a bad ECM or a bad ground on the engine. Taking off the MAF should make it start b****in as soon as its unplugged. Tried resetting the ECM connectors? Or if you can do one better if you got a spare laying around.

87350IROC

iTrader: (2)

Yup the ECM was my first thought too. I tried a new one. It made no difference.

As for grounds. The only one I messed with for the waterpump install would be the negative battery cable.

Let me add, I did get a code once I unplugged the MAF. Unplugging the Ignition Module to check timing also resulted in the correct code. But I'm not getting any codes with everything hooked up and running.

ResurrectingZ

Have you had a chance to check the power at the harness to the ECM? Also might check those fuses at the starter, its sounding more like it may be a power problem.

87350IROC

iTrader: (2)

I'll check that out this weekend.

Quick_Trans_Am

iTrader: (2)

I had a car that did this before. The solution, at least for me, was that I removed the MAF sensor, cleaned the carbon and gunk off of it with a mild detergent and water using a soft bristle brush, let it dry overnight, and reinstalled it. If you haven't cleaned it and wish to do so, be careful not to break the wire inside of it.