Houston_Z28

My 94 z28 6 speed
never start first try ever no matter if its hot or cold
the only exception is if its running and reaches operating temp than turn it off and turn it back on within 5 minutes.

ive changed my icm,opti,coil,new plugs,new wires and nothing (i changed the icm opti and coil because i had it all off to fix a oil leak which was the waterpump drive seal) any ways after all that it still doesnt start first try
after installing a new opti coil and icm the very first start of putting it all back toghter it started in literally a split second and startled me cause i just wasnt expecting it........

i have a video of my starting problem here:
https://goo.gl/photos/2CBowwYRMJzaAyw57

any help from a fellow lt1 enthusiast is much appreciated...........

Fuel pressure regulator is also new
And fuel pressure at rail is 40psi with fuel pump primed before and during cranking.

Fatdog2

Since nobody chimed inI would suspect bad or leaking injectors.Could also be the idle control valve.But instead of guessing,I would download GaryDougs free scan tool onto your laptop,get a cable or make one,and run a diagnostic test and post the results here so the pros (Injuneer and GaryDoug ect.) can analyze your results to pinpoint the issue.This will tell them exactly where the problem is instead of guessing and wasting time and money(which I've done to).Hope this helps.
When you have the scan tool hooked up ,start the engine (from cold )and drive it normally till the engine reaches normal operating temperature and then give the engine a couple of blasts,then drive normally for a while and then turn the stop button off on the scan tool.Upload the results here(there is info here on how to do this)and wait for the results.I don't remember the length of time to run the scan,but I think it's about 20 or 30 minutes to do this. Hope this helps.

gaedbo

To help you access the Free SCAN 93/94/95 software created by Gary Doug that Fatdog2 indicated in his post,

Click on the link below !

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

READ the information before you download it so you will know which download to select, and how it works.

You will need a cable and a laptop to use it. One of the places you can get a cable from is OBD Diagnostics

You can also make your own cable, the instructions are in the Scan link created by Gary Doug.

Injuneer the Super Moderator is able to read and diagnose the file if needed.

Injuneer

In a PM prior to this thread, I mentioned the fact that it sounded like it was cranking very slowly and labored. The dash volt meter immediately drops into the red, approaching 8 volts. Voltage that low affects injectors and the fuel pump.

I had a problem like that, immediately after the stroker was built. I blamed the slow cranking and hesitation to fire on the increased compression ratio, maybe the tune, the 74# injectors, etc. But the builder told me that based on the components used in the build, verified by measuring the torque required to rotate the engine, that would not cause a cranking problem. Engine was easier to spin than the stocker.

Based on having a stock starter exposed to the heat of headers for most of its life, I decided to replace it with a CVR Pro-Torque starter. The change in cranking was amazing.... went right back to starting almost instantaneously at the touch of the key.

I also mentioned the possibility of rapid fuel pressure bleed down, but he indicates he checked the pressure and it holds. That would rule out leaking injectors, leaking FPR, leaking pump check valve, etc.

Houston_Z28

I threw in my redtop optima battery from my 55 and no improvement. Maybe starter? I have longtube headers so it might be heat soaked if I drive on a hot day turn the car off for like 30 seconds then crank it again it cranks very very slow but it will start first try. Injectors are newish 36lb injectors iac valve is replaced along with the TPS as I had high idle and changed them both from a spare intake I had laying around which solved the high idle I now idle at 950rpm but after a couple days of driving it starts to idle at 1100rpm I unplug my battery for 15mins plug it back in and the idle if back down to 950rpm but that's off topic. My fuelpump is maybe 3 years old it's a Bosch plus I have good fuel pressure but could a week starter be the cause as to why when I crank my car the amps go down to 8? I thought new battery cables might be a shot to see if that fixes it but I've been waiting three weeks for them from summit and they still haven't shipped... Any tests to check the condition of my starter?

Injuneer

It's "volts" not amps. At 8 volts even the PCM can have problems. High current draw (amps) causes voltage loss if the battery is weak (no fan of Optima either), the cables and/or terminals are corroded causing high resistance, the starter is drawing excessive current (amps).

What happens to the fuel pressure when the starter is cranking the engine? Might be worth checking. I know the injectors will slow down at low voltage. Bosch fuel pumps are good, and last a long time, I run two of them in parallel, and one of them is over 20 years old. But all pumps lose performance when the voltage drops. For a performance application, improved wiring to the pump is a good idea.

Time to run a data log on the PCM. That will show what the actual voltage is at the PCM. Would also show what the programmed idle speed is, and how the IAC responds to the incorrect idle speed. Stock programming for an M6, fully warmed up, is 800 RPM. Will show the true idle speed, since the stock tach typically reads 100-200 RPM higher than actual.

When you disconnect the battery you lose the long term fuel corrections, and you may lose the learned IAC counts. You don't need to wait 30 minutes, it looses those stored values from volatile memory in a matter of seconds.

There is an IAC reset procedure:

Courtesy of Shoebox

4th Gen LT1 F-body Tech Articles

Fatdog2

I'm still new at this stuff but when you did the fuel pressure test and it read 40,did you let this stand for 20 minutes or so as to watch the gauge and see if it dropped or held 40 for a while?Just throwing things out there.My02.

Injuneer

Guess I should've copied and pasted my PM response, so everyone knows what has already been covered.

This is why I hesitate to respond to tech questions in a PM.

Houston_Z28

fuel pressure while cranking is 38-41ish holds pressure for the 15 minutes that I monitored it. I'm very sure that it's not fuel related. Because sometimes I'll have a day or two when it starts first try no problem then the next days it goes back to the usual....

gaedbo

Still seems like doing the Data Logging might help a lot.

Houston_Z28

I'm ordering​ a cable to plug it into my laptop will scan it when I get it. I'm assuming it's electrical as sometimes when driving I have close to 18amps for my battery and most of the other times it's low in the red zone like 10 amps. Could underdrive pulleys effect the alternator that much?

Injuneer

18 volts (not amps) is on the high side. But, if the starter is sucking the voltage out of the battery, when the engine starts, the voltage regulator raises the charging voltage to restore the battery charge, and bring the battery up to about 13 volts. As the battery voltage comes up, the voltage regulator reduces the alternator charging voltage, until the system stabilizes at about 13 volts.

So, it's normal for the voltage shown on the dash gauge to vary over a fairly wide range, as long as it follows the pattern described above.

Yes, U/D pulleys an cause poor battery charging, mainly at idle. Which pulley set do you have - U/D crank pulley only; U/D crank pulley + O/D alternator pulley (often used in vehicles with high electrical loads, like a high power audio system); or U/D crank pulley + U/D alternator pulley? I had the last one (25% U/D crank, 15% U/D alt) on my manual trans 94 and it did not adequately maintain the system voltage at idle (800 RPM with stock programming). There is so little engine power saving with U/D pulleys on the LT1 because of the belt not driving the water pump that I would rate them useless, and causing more electrical problems than they are worth. Dyno test of U/D pulley on an LT1 (power increase = 0.7 HP.... yes, less than 7/10ths of 1 peak HP.

Drivetrain Modifications #2

Houston_Z28

Okay so I'm leaning towards maybe the alternator..... When ever I put my foots on the brakes my amps drop, when I roll down my window my amps drop, when I turn on my radio amps drop, when put into reverse amps drop(reverse lights)
ill test my alternator tomorrow before I go to work. Alternator has warranty so hopefully that's the problem. Also when I go to start the car for the first time it cranks for about 5 seconds and then It try to fire like one cylinder is trying to spark or something like that.

Bleupold90

I just bought a 95 z28 6 speed with 120k some times it will start Wright up some times it want has full msd on it my low coolant light stays on even if it’s full has brand new fuel pump any idea what it could be thanks