Vellmen

Hello,

Purchased an awesome 94' Z28 back in June, it was bought from a friend who needed a car with better economy and who absolutely couldn't work on it.

It was running before the water pump went out, and I bought it knowing the new water pump had been haphazardly installed and was still leaking, the car at this point would not run. But interior and body were in great shape and i knew the engine not running wasn't catastrophic.

I finally figured out the leaking water pump shorted out the Opti-spark, ignition module and the coil. After changing them and fixing the leaking water pump problem the car would finally crank however it takes like 16 to 20 seconds for it to actually fire off. It's been this way for a while now with no change. The only time it will immediately re-fire is if I kill it dumping the clutch otherwise, anytime longer then say 3 minutes of ignition off it takes 20 seconds of cranking before it fires. If it's the 1st crank is several hours it starts and idles fine. If it sets only for a short time, it takes 20 seconds of cranking then fires, but idles at 2k for 30 seconds or more then idles down.

I took it to a local guy here in Panama City (only one in town I could find who could actually pull codes) and he told me it was possibly my security system. Told me to go get a security by-pass and install it since apparently a previous owner had already by-passed it with a home made resistor and wire. He also told me there were 3 codes before resetting the computer, after the reset the only code that came back was 36 "detects too many low resolution distributor pulses or not enough high resolution distributor pulses". I left and purchased a Vats Bypass Module at a local Lock and Key store, installed it and still have the exact same issues.

Obviously either ignition or fuel delivery is being cut by the computer and after cranking for some time it gets turned back on fires and away I go. So the question I pose today is do I need to back into the opti-spark? The disc inside with the windows, I know I made sure it was clean, and I am pretty sure it was installed correctly. Is it possible to install the disc wrong? Would it even run if it was? Am I seeing the result of this being installed wrong? Or do I need to look else where?

Is there any testing advise you could provide that would single out the culprit?

Any help would be appreciated. Thanks.

timnfxr

Check the fuel pressure. Key on engine off, it should be 41-47 psi after primed, and it should hold that pressure (within a couple of pounds). If it drops quickily, it's most likely the fuel pump.

RamAir95TA

I would agree with the above. Despite the issues you may or may not have had with the opti a slow start condition usually indicates a fuel issue.

Vellmen

Okay, thanks. Will start there.

Vellmen

Okay, just came back from checking fuel pressure. Here's what she does so I guess you guys hit the nail on the head?

Key on priming cycle reads 30 psi. As soon as the priming cycle finishes fuel pressure bleeds off and bleeds off quickly, say within 6 to 10 seconds and it's back to zero. Repeated this 3 times same result. I then started it and it runs at 30 psi, when I rev'd it a couple time it will jump to 40 and right back to 30 at idle.

Okay, $172 for the pump, but it looks like I'd pay someone $1000 to install it. I don't see any access to it from the hatchback area, which would lead me to believe the tank has to come out to gain access? Anyone know for sure?

Thanks.

RamAir95TA

Sounds like the fuel pump is the culprit. You also might want to check for leaking injectors and/or the fuel pressure regulator. Disconnect the vacuum line off the regulator with the key on and see if fuel comes out of it. Then pull up the fuel rail with the injectors still attached and cycle the pump looking for any stuck injectors. If those things check out okay then it's fuel pump time.

As for removal you have a few options.

Option A.) Drop the tank. This is a very time consuming laborious process. Many people consider this the "right way" as this is how the shop manual says to do so. The problem with this method other than the obvious is that if you don't do the install absolutely perfectly then you have to drop the tank ALL OVER AGAIN - a job that you won't want to have to do again.

Option B.) Cut an access hole. This method has been around for years and (for most) is the preferred method. Taking your time you can have the pump assembly out in an hour or so - likely less. Try a search for "fuel pump access panel" or something along those lines - you'll find a ton of info.

I have done a dozen or so installs through the hatch and, IMO, THIS is the right way to do it. Good luck.

Injuneer

There is a "sticky" at the top of the "Fuel and Ignition" forum topic listing with info on cutting a "hatch" for fuel pump removal.

I would also clear the codes, and see how fast the DTC 36 comes back. That's the code for a problem with the high resolution pulse signal from the optical cam position signal in the Opti. What brand Opti? The cheap Chinese rip-offs on ebay frequently arrive with a faulty optical module. The problem could also be caused by bent pins or corrosion in the connectors on either end of the short Opti harness.

Vellmen

Thanks for the awesome info, plenty of info and the picture tutorials are the bomb! Definitely going thru the hatch if the injectors pass the test!! I had already changed the fuel pressure regulator about a month ago which was leaking.

Yes, code 36 comes right back up tho. I installed a Cardone re-manufactured opti from O'reilly Auto parts. It was definitely a bargain compared to the others. I paid $150 for it so from what your saying I got what I paid for. I will certainly re-check the pins, don't remember seeing corrosion, and it's done this since I changed the opti. So, I plan to finish the fuel system 1st, obtaining the 41-47 psi fuel pressure without significant bleed off seems like it may fix the slow start issue. Then installing a "new" opti should clear the check engine light. Any suggestions on an affordable dependable opti?

Again thanks greatly for all the sound advice!