A Real C4 problem (LT1)-before I replace the Opti...

[socalman]

First, many of you have tried to help me diagnose my car and I thank all of you that have tried. This is my first stab at trying to fix a computerized/fuel injected car and I'm far from a mechanic. For the past 2 months (off/on) I've been using your help along with the FSM. (92 Auto w/ 52k miles).

The syptom started as an irratic idle running high/low sitting at a stoplight after running only 2 blocks, then when I went to go, the car bogs. I can get up to 30-40 mph, but the car shakes and chugs while getting there.

Sitting still, start up at cold, the car idles irradically but not enough to move the tach needle. After 15 minutes still sitting, the engine revs up and down from 600 to 900 3 or 4 times. I can get full rev sitting still, sounds smooth. Under load, bogs whether after warmed up or taking off immediatly from a cold start up.

No SES light, No codes.

My first question. Would the opti just take a crap, 2 blocks from your house with no prior warning (ran perfect until then)? I believe I'm down to Opti or ECM.

2nd question- can I use a spark tester by plugging it into a spark plug wire and then attaching the other end to the spark plug while still in the block?

3rd question- FSM and some of you have suggested many times about tracing ground wires. Almost all the ground wires, including from the ECM run to one bolt, bolted into the back of the block under the driver side head- impossible to see or get to. But, figuring that everything else works on the car, if there were a ground issue at the final connection, I'd be having problems with other things?

The FSM refers to using the Tech 1, which is tough to find, for many of the testing procedures. Most sensors and the coil module, all refer back to getting a reading on the Tech 1, so I just started replacing parts. I figured it was 18 years old so I'll know that part is now new (kept the old parts for back up now that I know they're still good).

Here's what I've tested or replaced

1.) Spark- new coil, coil module, wires and plugs (what a bitch!)
2.) Fuel filter, Bosch III injectors (pump tested 41psi, 39psi under load)
3.) O2 sensors replaced
4.) Manifold vacuum, hoses etc.- all under specs
5.) PCV valve & hose replaced
6.) MAP sensor replaced (no MAF on 92)
7.) Air Filter replaced
8.) I have the temp sensor and IAT sensor to replace, but haven't yet.
9.) Tested EGR- ok
10.) Tested Cats- zero back pressure (ok)

Thanks for any help/direction you can give.

[Frizlefrak]

One last thing before tugging that opti out of there....have you tested/replaced EGR valve?

[PLRX]

Originally Posted by Frizlefrak

One last thing before tugging that opti out of there....have you tested/replaced EGR valve?

[socalman]

Originally Posted by Frizlefrak

One last thing before tugging that opti out of there....have you tested/replaced EGR valve?

Forgot that one, yes I tested the EGR- all good. Also tested for plugged cats- Zero back pressure. I basically tested everything I could without the Tech 1 using the FSM.

Any thoughts on using the spark tester the way I described or will I damage something? (is it only for testing coils?)

[socalman]

Originally Posted by PLRX

Car repairs are no laughing matter. There's to be no fun in this thread

[Taurus]

Originally Posted by socalman

Forgot that one, yes I tested the EGR- all good. Also tested for plugged cats- Zero back pressure. I basically tested everything I could without the Tech 1 using the FSM.

Any thoughts on using the spark tester the way I described or will I damage something? (is it only for testing coils?)

How about the ignition module? Same thing happened to me and that's what it was.

[Frizlefrak]

A spark tester is really only going to tell you if you have spark or not....not the strength of the spark. Are you thinking completely dead cylinder? But your infrared thermometer readings were all relatively close, correct?

[Frizlefrak]

Originally Posted by socalman

Car repairs are no laughing matter. There's to be no fun in this thread

BAN THEM!!!

[socalman]

Originally Posted by Taurus

How about the ignition module? Same thing happened to me and that's what it was.

I'm putting on my dunce cap- Ignition module...same as Coil Module (or Driver as referred to in FSM)? I did replace the coil and driver.

Originally Posted by Frizlefrak

A spark tester is really only going to tell you if you have spark or not....not the strength of the spark. Are you thinking completely dead cylinder? But your infrared thermometer readings were all relatively close, correct?

They were sporatic at best. I would get from 200 to 360 depending on how I was holding and aiming it. Cylinder 1 pretty conisitant at low 200's while 3/5 would be 360-80 and Cyl 7 come in at 280-320.

[PLRX]

Originally Posted by Taurus

How about the ignition module? Same thing happened to me and that's what it was.

thats what I wanted to write earlier but, couldn't come up with the f name.

That is 85% of the reason people start an opti thread and is not the opti.

[socalman]

I have the Opti, WP, new hoses, thermostat and bypass sitting in the garage. Put in the new Injectors last night and was hoping...but it was

If my Opti is still good, I'd like to not pull it, so just trying to figure out if there's any other way to test things.

[Frizlefrak]

If memory serves me correctly (which is a crapshoot these days) you couldn't find anyone that could test the module, correct? So it has been replaced?

[socalman]

Originally Posted by Frizlefrak

If memory serves me correctly (which is a crapshoot these days) you couldn't find anyone that could test the module, correct? So it has been replaced?

Dogs have better memories than you think. Yep, replaced, nobody could test. I've sure got a collection of backup parts though

[PLRX]

Originally Posted by socalman

Dogs have better memories than you think. Yep, replaced, nobody could test. I've sure got a collection of backup parts though

did a little mod to the animation

[Frizlefrak]

We're running out of possibilities. It's getting down to PCM or Opti. You know I hate replacing parts and spending money unless it's a must, but if you already have the parts bought, may as well change them. I don't know of any way to test a PCM either, other than eliminate everything else from the equation. I have seen them fail and never send out a distress call either.

Roll up you sleeves....gonna be a long weekend.

[five-oh]

Originally Posted by Kimmer

Auto Zone advertises it tests icm but they cant test ours.

Hmmmm... the local Autozone tested my icm off of the '93 last year. Tested faulty, replaced it and it worked.

[Frizlefrak]

Originally Posted by five-oh

Hmmmm... the local Autozone tested my icm off of the '93 last year. Tested faulty, replaced it and it worked.

Could be the roasted possum and the quart of 'shine had something to do with that.

[five-oh]

Originally Posted by Frizlefrak

Could be the roasted possum and the quart of 'shine had something to do with that.

'Possum- probably not. Moonshine, however, makes EVERYTHING better.

[Frizlefrak]

Originally Posted by five-oh

'Possum- probably not. Moonshine, however, makes EVERYTHING better.

Hell, I woulda just handed you a new Opti for free, just in case the module didn't fix it.

[socalman]

Originally Posted by Frizlefrak

We're running out of possibilities. It's getting down to PCM or Opti. You know I hate replacing parts and spending money unless it's a must, but if you already have the parts bought, may as well change them. I don't know of any way to test a PCM either, other than eliminate everything else from the equation. I have seen them fail and never send out a distress call either.

Roll up you sleeves....gonna be a long weekend.

I guess so. Not this weekend, it's shot. Not next either- heading to Lost Wages.

Originally Posted by five-oh

Hmmmm... the local Autozone tested my icm off of the '93 last year. Tested faulty, replaced it and it worked.

Can't remember what it was, but the icm for 92 only fits the 92 Vette and 93 F body- somethin like that. I went back to the same store and 4 others, looked in thier books. No pigtails and no listing in their books for that particular part so they had no way to test it.