Troubleshooting an Extending Cranking before starting Problem!

[LeeS97Z28]

Hi Guys!

I have a 1997 Z28 with 86Kmiles on the clock.

First, let me tell you what I have done to the car...I have replaced spark plugs and wires, EGR Valve, Ignition coil and Ignition Module, MAP sensor, IAT sensor, Cleaned the throttle body and replaced gaskets in it, New fuel pump(AC Delco). I also cleaned the Mass Airflow sensor.Brand new Optispark distributor done by dealer!

Now the problem....It takes 3-5 seconds of cranking to start up. When it is idling, you can hear popping in the exhaust like it is missing a little. It seems to bog a little bit too like it isn't getting enough fuel.

The only things left to replace are O2 sensors Mass Airflow sensor, engine coolant temperature sensor, and knock sensor.

Now it doesn't matter if it is cool or hot it still does the above just the same.

Looking at the car on a scan tool the O2 sensors change rapidly.
It has 19.5 Hg of vacuum.
IAC Counts are 30
Long term fuel is 132 on left and 130 on right.
Fuel Pressure is 43psi idling to 46psi if you blip the throttle WOT.

Do you think I need to replace all the injectors and fuel pressure regulator?

[Joe 1320]

The first thing I would check is how quickly fuel pressure ramps up once the key is energized but the engine not started and how long it holds that pressure. Next would be a good injector cleaning. I've seen them last for double those miles, I've seen them fail with less than what you have so it seems to be a crapshoot. For utmost performance, I don't like over 50K miles of use. If you think the injectors are the culprit, try swapping them from side to side and see if the fuel imbalence switches sides.

[fastTa]

Just based on your input, it sounds as if you are getting "lean popping" from lack of fuel delivery. If you have a GM enhanced parameters scanner, it will likely have the capability to pulse each individual injector for diagnosis purposes.

1.Put a fuel pressure gauge on your Shrader Valve, turn the key on but dont start. The fuel pressure should hold steady at at least 43-44 PSI. Take note of what this fuel pressure is without the motor running.

2. Then turn off the key and make sure that the fuel pressure holds steady at this same pressure for at least 4-5 min. If it does not, then you either have a problem with the FP regulator, the check valve, or a leaking injector.

3. Get the scanner hooked up and ready and make sure the motor is NOT running. Begin the injector pulse test cycle. Ususally you have to manually move to each injector on the scanner. The scanner will confirm when each injector is being pulsed.

4.. While each injector is being pulsed, there will be a slight "dip" in the fuel pressure reading on the gauge (approx 10 PSI), but it shouldn't be too much more than this. If the fuel pressure reading does not "dip" at all while a specific injector is being pulsed, then there is a problem with that specific injector.

Are you getting any cylinder misfires? When you say the 02's are switching rapidly, how rapidly and how much of a difference?

Another test you can do to see whether or not a cylinder is misfiring is to use a laser or infrared thermometer on each primary of the manifolds/headers. Let the manifolds/headers cool completely then fire up the motor. After about 30-45 seconds, check each primary for temp and see if there is one primary that is significantly cooler than ther rest. On stock manifolds, you will have to point the thermometer at the outside of the primary on the 4/6 and the 3/5 due them being siamesed.

[N20LT4Bird]

THese are all good suggestions....smart guys around here. I would first check the fuel pressure issue....a leaking injector? Another basic parameter to check is the coolant temp. It may still be in range to not set a DTC, but be off enough to lean the mix out.

ANd if you dont have a MAster Tech scanner or one capable of pulsing injectors as Kevin descibes, you can buy a generic pulse tester. OTC makes one for about 125 bucks.

[Injuneer]

How does the starter sound? I know after the stroker rebuild, I was sort of disappointed at the time it took to start. We checked everything in the ECU, the fuel pressure, coolant temp sensor, etc. I thought maybe it was the stroker itself, but the shop told me they had checked the torque required to turn the crank and it was less than the stock engine.

I finally replaced the starter, and all the problems were solved. Starts with the first turn of the key. The starter was apparently drawing too much current, and pulling down the system voltage enough to affect the spark and the injectors.

It was not on a stock PCM, but the problem would affect the stock similarly to the aftermarket ECU, I would think.

Just another stab in the dark.....

[LeeS97Z28]

Thanks Guys!

What would be the best scanner to get to do the GM Enhanced parameters for my car.

I can spend $600.00 on a scanner

[fastTa]

Best best for the money would be to use a PC based scanner software and a cable to connect to your ALDL.

Thank Fred for this! He likes typing way more than I do!

http://members.aol.com/FWForsythePE/HowTo/Scanner.htm

[Injuneer]

Problem is the links in that writeup are sort of out of date. But it will give you an idea of what's out there.

I was recently shown a link to an OBD-I system that I haven't seen before, by EFILive:

http://store.efilive.com/

[LeeS97Z28]

Update!

Hi Guys!

Here is the order I did the test on my fuel pressure.

1. Engine sat overnight turned key on (once). I got 40psi fuel pressure.
2. 20 mins later I got 38psi (car not started ).
3. Started car got 38psi. ( car idling).
4. I took off the vacuum line to the fuel pressure regulator and got 47psi.
5. Put vacuum line back on got 38psi.
6. I just shut the car off. I got 28psi of fuel pressure.

Please note when I turned the key off, I didn't turn it back on to prime it either. This happens when you just shut the key off and look at the fuel tester.
I noticed when I unhooked the vacuum line to the fuel pressure regulator and got 47psi the car did Idle better. But it still had a little popping in the exhaust.

I think the injectors are dirty don't you? Do you think they are bad enough to replace since the fuel pressure dropped 2psi in 20 mins?


Thanks Lee?

[fastTa]

You really need to perform the injector pulse test first. Then, if that seems fine, you might want to lift the fuel rail/injectors and look for a leaking injector. Could also be a sticking FPR?

I'm also assuming you replaced the fuel filter when you did the fuel pump?

[LeeS97Z28]

Hi fastTA!
Yep the fuel filter was replaced at that time. The fuel pressure builds to 47psi which is within the upper limits of normal but only if you remove the vacuum line from the fuel pressure regulator.

I am going to order a scan tool monday that can do the Enhanced GM commands like misfire monitor and fuel injector balance tests.

How long should it hold fuel pressure before leaking off? What would be considered normal leak off?

Thanks again Lee!

[fastTa]

A 2 PSI "bleed off" would be considered acceptable over a 20 min period.

The "stand alone" enhanced and graphing scannes are big bucks! Do you own a laptop? Can you borrow one? Heck you can get a "good enough" laptop on eBay for a few hundred bucks. It would be very beneficial to get your own software for use on a personal computer.

[LeeS97Z28]

Found Some Fuel Injectors by Racetronix what do you think about them?

Hi Guys!

I found these fuel injectors at this linkwww.racetronix.com
Look at the 24lb injectors by delphi. They are disc type would these work just as good as the original GM injectors or not?

I'm prepared to by either the original GM injectors from Jason Cromer or buy these from Racetronix. Since I need to replace the fuel pressure regulator I'll do the injectors too.

Let me know what you guys think!

Thanks Lee!

[Injuneer]

The disc type injectors are faster acting, and might need a tweek of the "offsets" in the PCM. But you could probaly swap them out with no affects. Ask Racetronix. They will know how much difference there is and whether the programming needs any changes. I'd guess no changes required.

[BANSHEE001]

I had the same proublem. what it was for me was. when I did a tune up on my car I had to pull the in take hose off to get to the parts. I ended up putting a small cut in the bottom of the rubber boot that connects to the intake. So it would take time to start because off vacum loss to the trottle body. But it wasn't a big opening so it would start but get a popping sound in the motor when I gave it gas. good luck.