Kempster

Hey guys, I've been reading the forums for a few days and trying to diagnose but I'm running out of money and ideas.

Car was running, I turned it off for a few minutes and it has not started back.

Starting fluid got the car to start for a few seconds, so I changed the fuel pump (trap door method), fuel filter, and pump relay. I'm getting 45psi at prime, but it slowly tapers off to 0. Never starts.

Also starting fluid will not start the car anymore. I had a few people look at it and they all said weak spark, so I just spent the entire day changing out the opti and still no start.

Symptoms are cranking strong, but at the end it putters a few times without starting. (slow putters, pew......pew.... ....pew and a puff of white smoke out the intake).

I checked 2 of the spark plugs I could easily reach for gas, or any signs of anything. A little carbon but dry.

I haven't changed the ignition coil but there are no codes. Like I said, I'm out of ideas. I've had this car since feb, it is in almost immaculate shape and has +150k miles.

Ideas? I've been on it all day so I'm about to go home, the forums have given good ideas but I haven't seen many with my year model or symptoms. Hopefully one of you can help me, cause between what I still owe and what I've already spent it's starting to make me sick.

Maybe I didn't line up the new opti right, but symptoms are no different between old and new opti. A mechanic buddy is bringing a legit scan tool to monitor the motor, hopefully that'll shed some light.

Kempster

I can tell the old opti is bad, lots of resistance and jumpy when spinning the wheel, so maybe I just jacked up the timing. I'll give that another look just in case (as I bang my head against the wall for reinstalling everything)
Lesson learned.

Injuneer

Did you open the old Opti up - sounds like the rotor may have come loose, or shattered?

Kempster

Haven't opened up the old one yet. I pulled off the new opti last night to check the timing, and now it doesn't putter after cranking.

We did use a high dollar scan tool and found that temp sensors are messed up. Mechanic buddy was guessing that with it reading -40* F that it was flooding the car keeping it from firing.

Changed the water pump and head sensor. Still reading -40*. Gonna check the wiring harness. Would that eliminate all spark?

Injuneer

Test the coolant temp sensor in the water pump and the wiring, using Shoebox's guide:

4th Gen LT1 F-body Tech Articles

Low temp results from a high resistance. An open circuit on the wiring will have infinite resistance, and generate the lowest possible CLT temp.

You mention "sensors" (plural).... only the coolant temp sensor in the water pump connects to the PCM. The one in the driver's side head does not. Some scanners will report the oil temp sensor at -40*F, but that's because the F-Body LT1 does not have an oil temp sensor..... the Corvette LT1 does.

A constant reading below -40*F on the coolant temp sensor should set a code - P0118.

The PCM will not shut down fuel or spark due to low coolant temp. When the code sets, the PCM will default to a programmed CLT temp, and run the engine using that.

Kempster

An update:
My 97 z28 actually has 429k on the now working odometer, so adding in the 4 years I was guestimating this motor has 460k on it.

To fix all that was wrong involved replacing the icm and coil and a few bad grounds.

Fast forward to now I've had another opti installed about 3k miles ago and I'm getting both resolution codes from the opti (mostly low, but after stalling occasionally I'll get high).

The car will typically start with varying quickness, but it will idle to about 180* then progressively bog at 4k, then 3k, 2k, then eventually it won't turn over. (Throws low res code here).
After letting it sit about 12 minutes with random attempts to crank occasionally itll fire and bog. Continuing to try it will eventually idle but bog at 2k, then 3k, then 4k until it will run fine. Blows white smoke during bog, and it sometimes sounds like the motor is running in reverse, knocking and blowing smoke out of the intake when trying to recrank. That's not everytime but its happened a few times and is quite alarming.

A lot of times it will not fire up after a bog and kill the battery while cranking, but if I let it sit long enough (days) it'll fire up with one turn of the motor.

My question is that I've checked the harness wires and all voltage and resistance is fine, and the shop that installed the opti says that it and the icm are fine. Any other ideas?

Live scan shows that O2S12 volts aren't varying alot at temp (staying between .065 and .075) and fuel trims SHRTFT12 and 22 stay at 99.2% each. Sparkadv is approx 15 at idle, 45 with throttle.

I can add full scan notes if needed but these are the only ones that appear off to me (but I'm just a street mechanic, so idk)

Injuneer

If you have the low res Opti code and the engine will not start, and there is no spark (have you checked) and the injectors are not firing (have you checked), there is a problem with the optical module in the Opti. They do suffer from heat soak. What brand was it? Most of what's out there are cheap Chinese ripoffs. Some of them fail right out of the box, some fail after a short period. Saw an interesting thread on another site where an electrical engineer opened up the optical module of a Chinese cheapie, and found a weak point on the PC board that opened the circuit as the module heated up, and reconnected the circuit when the module cooled down. He was able to repair the PC board.

When you say "'I've checked the harness wires and all voltage and resistance is fine,", did you run Shoebox's test on the white wire to the ICM?

4th Gen LT1 F-body Tech Articles

Note that the "Opti" portion of that procedure only verifies the PCM is supplying the required voltage to the Opti. IT doesn't check the signals the Opti is returning to the PCM. But if you don't have the AC voltage on the white wire to the ICM, you aren't getting the low res pulse from the Opti.

Hard to decipher your O2 nomenclature. The driver side pre-cat O2 is B1S1, driver side after-cat sensor is B1S2. Passenger side pre-cat is B2S1, after-cat is B2S2. If a pre-cat O2 sensor is stuck that low, should set a code. I've seen after-cat O2 sensors hang low, but that could be an issue with the cat, not the sensor, and that should set a code too. The scan software I have seen reports the after-cat O2 LTFT's at 99% because the 96/97 LT! system doesn't actually have LTFT's for the after-cat sensors.

Kempster

Thanks for the quick reply.
I'll have to do that test with the white wire. Before I had checked resistance through opti harness then I checked voltage from the end that connects to opti, but dont remember the volts, but I remember it being similar to internet results. I'm not sure the brand of opti, I just made the mistake of trusting a shop to do the right thing. But that could be the case with the chinese opti because it's the symptoms of a bad coolant temp sensor but throwing opti codes, where it's ok cold and ok hot, but it is absolutely horrible thru the transition.
As far as the O2s, I got a code for bank 2 last night. From my last post I got it to crank, went thru the bog time, then got it to crank again and I drove the car and let it idle approx 12 hours and other than the cat code no problems or stumbles.
I haven't done the icm space cool mod, but I probably should. I noticed my engine temp through the live scan tool was hovering about 240 while my gauge said 200, so it's def hot.
I also believe there is an exhaust leak because I can hear the tiktiktik under there.
The car is starting to resemble the mileage. Thanks Inj.

Kempster

Cat code being 0430. Love the car but with the mileage I'll be driving it til it blows up.
Thought about maybe converting it into a hydrogen project/experiment. Jury is out on that though. I'm interested in Stanleys water powered cart, maybe make something happen.