Retracy53

Okay so I have a '94 Z28 that I bought a few months ago. When I bought it the head gaskets were blown. I replaced all that and put it back together to find out the opti went bad. So I then replaced that as well.


After replacing the optispark, it ran fine and would idle fine. The next day it wouldn't start unless the throttle was held open and then wouldn't idle. Then shortly after wouldn't start at all. Due to that I replaced the fuel filter and Fuel pressure regulator. After replacing the regulator I'm back to being able to start it with the throttle open.


During the whole process I have replaced:

-Head Gaskets (as per original project)

-Optispark

-Ignition Coil

-Spark Plugs & Wires

-Fuel Filter

-Fuel Pressure Regulator


My fuel pressure with turn-key on engine off is 42 psi. However, once the fuel pump shuts off it jumps down to 38 psi. While cranking it's 42 psi again.


I have also ruled out a clogged catalytic converter as I have disconnected the downpipe from the exhaust manifolds.


Deleted on the car is the:

-EGR System

-AIR Pump

-A/C (But that seems irrelevant in this situation)


The AIR check valves aren't plugged off yet but it ran and idled without plugging them off.


If anyone has any ideas I would appreciate it.

Injuneer

Have you scanned it for codes?

When you hold the throttle blades open, it puts the PCM in “clear flood” mode. PCM reduces fuel flow through the injectors. May be indicating a faulty coolant temp sensor (the one in the water pump housing) showing an incorrect low temperature, which results in the PCM setting an excessively rich cold start A/F ratio.

When the fuel pump primes for two seconds and turns off, is that when you see a max of 42 PSI, and it shuts off and drops to 38 PSI, how long does it hold 38.PSI without dropping further? We're looking for signs of a leak in the fuel system, possibly an injector.

Retracy53

I haven't been able to get any code scanners to work on it so far so I'm not able to get any codes. But the check engine light does appear after trying to keep it alive for a little.

As for fuel pressure, yes the 38 psi is after the 2 seconds the fuel pump stops priming. It drops to about 34-36 after about 20 seconds. The lowest I've seen it get to is 32 psi. Even after a few minutes it doesn't drop below that.

I belive you're onto something with the injectors. Nonetheless I will double check the injectors and the coolant temp sensor tomorrow when I work on it again.

Injuneer

If the fuel pressure stays in the 30’s after a period of time, probably isn’t a leak. A leaking injector will usually cause a rapid drop.

You need an OBD-1 scanner. An old AutoXray is adequate. Or a combo OBD-1/OBD-2. Actron often can be found discounted on Amazon for under $100. Avoid Innova and Equus, they have a corrupt data base for the LT1 and show incorrect codes. And simple “code readers” like the Actron 9001 will not work on a 94, because they just short the DLC pins, and 93 was the last year you could flash the codes on the SES light by shorting the pins.

Then there is free scanning/data logging software, Scan9495 specifically for the 94/95 LT1. Scans PCM, ABS, and air bags. The author is a member here.

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

When the SES light comes on do the radiator fans turn on?

Retracy53

I don't have the fans in right now. I was trying to make sure the engine ran good before I put coolant in and put the fans in.

I picked up a new temp sensor today it seemed to help a little but it still seems like the car is flooding itself still. What I mean by that is when I turned the key it fired once but didn't start. Then it wouldn't actually start until I held the throttle open.

I should note that it took a little to even get this to happen. Once I replaced the sensor it would backfire through the exhaust on about every 3rd crank with the throttle open.

I loosened the temp sensor a little and it started a little easier. Is it possible that I have the sensor too far in for it to work properly?

Other than that once I did get it started. It would idle just fine at 1k RPMs with a slight touch of the throttle. When I let off it would drop down to about 500-600 RPMs and sound like it wanted to die but it would stay on until I shut it off.

Even warm it would not start without throttle, however it did idle better. It has not been tuned for an EGR delete, and the AIR valves aren't plugged off. Could this contribute to anything?

As for the OBD1 code reader I'm still waiting for one. My local O'Reilly's has a scanner with a GM adapter but when I borrowed it, it wouldn't even turn on.

Nonetheless I do appreciate your help and advice.

Injuneer

With no coolant in the system, makes one wonder how accurate the coolant temp sensor reading is. Did I miss this “no coolant” condition? That would have been useful. Are the air intake ducting, IAT sensor, and MAF sensor all connected and in place?

What do you mean by “the AIR valves aren’t plugged off”? The valves are check valves. They allow air to flow into the exhaust manifolds when the AIR pump is running, and they prevent exhaust gasses from flowing out of the manifolds when the pump is not running. Are they still screwed into the manifolds? And there are just no rubber elbows connecting the valves to the metal pipes from the AIR pump? The valves can corrode and allow exhaust to escape. Or if partly open they can allow the fast moving exhaust to educt air into the exhaust stream, screwing up the O2 sensor readings. But that may not be affecting how the engine runs, see next paragraph.

Without the coolant temp sensor showing the engine is warm, the PCM is probably still running in “open loop”, meaning the PCM is ignoring the O2 sensor readings, and unable to attemp to adjust the A/F ratio to correct for a perceived (false) lean condition. The PCM can't go into “closed loop” and control the A/F ratio until the coolant reaches a certain temperature (variable, generally in the range of 120°-140°F), the O2 sensors are hot enough to start working (~600°F), and a timer(typically 206 seconds run time) has timed out. Then it can start controlling the A/F ratio. But if the coolant temp sensor is showing a low temperature, the PCM richen the A/F mix for cold start, and elevates the idle speed.

I think you need to put things back together before getting any meaningful results.

Then there’s the issue of “dropping the down pipe”, assuming you have disconnected the Y-pipe from both exhaust manifolds. The driver side O2 sensor is in the manifold, but can’t be accurate because of the backwash of air into the manifold, and the passenger side O2 sensor is in the Y-pipe, so it's not seeing exhaust, and reporting an extreme lean condition based on pure air.