PurpleHaze95

When I got my '95 Z28 out of storage on July 1 it started right up and ran fine. I drove it from the friend's place where I had stored it to Costco where I put gas in it. After that it again started up fine, and I drove it to the car wash where I renewed my Fast Pass. Then I drove it home and parked it in the driveway. The next day I got in it to drive it and it wouldn't start. It kept trying and trying but wouldn't turn over. Finally it started but was idling really rough. I thought maybe it just needed to get moving a bit, so I headed down the street from my house. It kept idling rough, and would occasionally surge in RPMs. A few houses down I decided trying to go anywhere was a bad idea, so I turned around and went back home. Two houses down it settled into a proper idle, but then when I hit my property line it just flat out died. I was able to get it started again and limped into the driveway.

Since then it has run fine for long enough to move it to a different spot on the driveway, then didn't want to run, then ran fine for a few trips around the block, and just last night didn't want to start again. Our thinking is either that something is up in the fuel system (fuel pump or fuel filter) or that the opti-spark is going bad. My brother and I tested the fuel pressure and it's right within the normal range, and when I turn the key to accessory I can hear the fuel pump whine quietly as it pressurizes the system in preparation to run, so while we can't rule out the fuel system entirely we're thinking that's probably not the cause of the problem. That leaves the opti-spark. The water pump had to be replaced within the last few years, but at that time the opti-spark was deemed to be okay so it wasn't replaced. What do you all think: time to replace the opti-spark?

If you agree it's the opti-spark, does anyone have any recommendations for a really good replacement one? I think someone mentioned that it's possible to get encased ones, so if the water pump goes out again it won't get damaged.

Injuneer

Have you scanned it for codes? .... checked for spark at the plugs when engine is cranking? Did the car wash inlude an under chassis wash? How many miles on the Opti? Original or replaced at some point in time? If replaced, what brand?

What was the fuel pressure reading after prime? ..... during cranking? ... at idle with and without the vacuum compensation line attached to the fuel pressure regulator? Did you try and measure the pressure on the road with the engine under load?

PurpleHaze95

We tried to scan it for codes, but two things: #1 until this evening the check engine light was not on, and #2 we discovered it's an OBDI vehicle and the scanner we have is only OBDII. The car wash was just basic and I don't think it included undercarriage wash/spray but I am not 100% sure. AFAIK the opti is the original one on the car, because it has only 55,000 miles on it.

I'm going to have to refer you to my brother on that one, because he was operating the pressure tester while I was sitting in the driver's seat.

This evening I tried starting it just to see if it would run, and it was reluctant initially but started after a few moments and stayed running long enough for me to drive it through the portico onto the main part of the driveway. For once in my life I was glad for a driveway that goes downhill, because I was able to put it in neutral and roll it down to the curb so a tow truck can pick it up if necessary. (We have a house full of boxes to unpack following a house fire...)

TheNovaMan

Priming fuel pressure gets up to 38 or so. Idling it's 35-36 with the vacuum hose on. I didn't think to take it off until a couple days after I had returned the pressure tester. I didn't have the opportunity to check it when it was misbehaving, but I don't think it's a fuel issue - even if the pressure isn't quite up to snuff, it should try to run. When it misbehaves, it mostly just cranks and cranks without a hint of firing.

Injuneer

As far as scanning, there are codes that do NOT turn on the SES light, like DTC 16 for the Opti - that code shuts down the fuel system, after prime. You have to scan.

When cranking, and not starting, check for spark at the plugs.

This test from Shoebox will tell you if the PCM is getting cam position info from the Opti, and sending the signal to the ICM to fire the coil:

4th Gen LT1 F-body Tech Articles

Heat soak would explain the problem after it's been running for a while - ICM, Opti optical module, fuel pump. But not starting when it's cold wouldn't seem to be related to heat soak. Maybe moisture from the car wash caused problems with corrosion on the plug and coil wire terminals at the Opti. 22 years take a toll, even though its only got 55 K on it. I would have the ICM tested - make sure they get it good and hot, and check the wires for corroded terminals.

There is always Scan9495 to pull the codes, but does require a 16-pin OBD-1 cable.

https://www.camaroz28.com/forums/com...95-lt1-874306/

Or a 12-pin cable with adapter wires, as shown on Shoebox:

http://shbox.com/1/xraycable.jpg

As far as the fuel pressure, should prime to at least 40 PSI before the pump shuts off. It should hold that pressure after the pump shuts off, with minimal drop off. At idle, 35-36 PSI is OK. Without the vacuum line, it would have been closer to 44 PSI. Did you watch the pressure as you try to crank it, but not starting?

TheNovaMan

Thanks for all the pointers, but she had it towed to a reputable shop, and they said it's the Opti. She ordered the Petris Opti on my recommendation, and they're going to install that along with new plugs, wires, and a serpentine belt.

Injuneer

Be interesting to see how the Petris works out. Odd that their tech writeup totally ignores the fact that the Opti was used in vehicles other than the Corvette. A would also question the accuracy of their statement regarding injector timing problems with loss of high resolution pulse, and their logic behind the addition and purpose of the crankshaft position sensor.

Let us know how it works out.

PurpleHaze95

Thank you for all your helpful comments, Injuneer. If we had more free time my brother and I might have taken advantage of some of them and tried to solve the problem(s) with my Z28 ourselves. As it is, though, "free time" is sadly a pretty much non-existent thing for both of us this summer due to some things that have happened in the last six months or so. I considered the situation carefully and decided that if I want to be able to drive the car this summer instead of fussing with it I should just put on my big kid pants and pay to have it fixed. Otherwise I could easily see us fixing one thing, only to have something else need to be fixed as well, and so on down the line in that manner. (He's already trying to fix his waterskiing boat in much that same trial-and-error method.)

I got the call this afternoon that it's finally finished, so I will let you know how it goes the next few weeks!