real82it

95 Pontiac firebird 5.7.

Car died while driving down the road.

Won't start. Had to get towed home.

I have fuel pressure and spark at coil and at plugs (checked #1 & 7)

Checked injector harness with NOID light. It is ok.

Checked TPS. Ok.

No DTC codes.

I am running an aeromotive boost referenced fuel pressure regulator. 255 Walbro pump. I am running an MSD 6 BTM box with MSD opti.

I would normally suspect the opti or MSD box, but since I am getting spark at coil and plugs, does this mean that opti is ok?

When I Checked fuel I get pressure at key on and while cranking, but if I go key on without cranking, pressure spikes then drops very quickly sometimes. Other times it holds pressure.

With fuel pressure, spark, and no codes, don't know what else to check. Any other ideas?

Here is a video of key on pressure drop.

95 lt1 fuel pressure loss after key on - YouTube

Injuneer

Did you try starting it with the accel pedal on the floor? Put it on the floor BEFORE turning the key to start and keep it there until the engine starts.

Check the vacuum line for the fuel pressure regulator for wet fuel. The Aeromotive AFPR's are prone to failure.

real82it

No fuel in the vacuum line to the FPR.

I will try the pedal on the floor tomorrow. What does this do?

shoebox

When some people say "no DTC codes" they mean no check engine light. Did you actually scan for codes? Did you use a scanner to check the TPS? What did your TPS check consist of?

Holding the throttle to the floor puts the PCM in "clear flood mode", meaning it stops injecting more fuel in case it is flooded. Have you looked at any spark plugs for fuel?

GaryDoug

Putting the pedal to the floor while cranking puts the pcm into Clear Flood mode, meaning it won't operate the injectors, assuming the engine is flooded with fuel. Leaking injectors and/or bad coolant temperature sensor can cause flooding.

real82it

I tried to start the car with pedal on the floor - nothing changed. No start.

I am using a freeware obd1 monitor program to check codes and TPS position. I remembered I have TTS data master on my old laptop - I will hook that up and look at the full code able to see if anything shows as red.

Injuneer

GaryDoug's Scan9495 is a better data logging program, free download available. Produces a .csv format report that I prefer to review, without the laborious conversion from TTS's .uti

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

real82it

I used the scan program that was recommended.

No DTC codes.

I did verify the TPS was working correctly.

Scan file attached.

Still can't get car to start.

Any ideas on what I should look at next?

wjogert

That pressure drop would suggest a leak... be it an injector (stuck open or held open by bad pcm), fuel return line, or a physical leak.

I would unplug one injector at a time, check key on pressure, and check signal pulse at connector while cranking.

Pull spark plugs and check for fuel or fouling. Maybe check cylinder compression at same time (maybe timing chain jumped or broke).

Crankshaft sensor? I can't remember if Opti will spark at all without a signal from the crank... ??? But if it could, it would be well out of timing.

Injuneer

Rapid pressure bleed down can also be due to a faulty check valve in the pump.

Another way to check for leaking injectors is to pull the rails up and prime the system (DO NOT TURN THE KEY TO "START"), and look for drips. If the PCM was constantly supplying a ground to hold an injector open, there should be DTC 18 for the injector circuit.

93-95 does not have a crank position (CKP) sensor. The crank position sensor was added as part of OBD-2 in 1996. The only purpose is to detect misfires. All yeas will start and run without the CKP sensor. The PCM only needs the cam position pulse signals from the optical module in the Opti. Without the low resolution pulse it sets a DTC and shuts down the fuel pump and injectors. Fatal code it DTC 16. If the injectors are pulsing and there is spark, the Optical module is doing its job. Quick check is to watch the tach when cranking. If it moves to ~250 RPM the cam position signal is present.

A possible problem with the Opti that does not set a code is the rotor screws falling out, which will obviously screw up spark timing. But you will usually get a few cylinders firing, at the wrong time.

I'll take a look at the data log in a while.

Injuneer

First, fix the date on your PC. Log indicates the date is 27-July-2004

Log runs for 113.65 seconds. VATS is met. Appears your location is quite a bit above sea level, based on barometric pressure.

PHASE 1

First 36.39 seconds shows no activity, and a steady system voltage of 11.8 volts. No codes. Is this correct - you did not try and start the engine?


PHASE 2

At 36.39 seconds, you crank the starter. System voltage drops to a level that may prevent it from starting. The first few frames show voltage drops to 7.8 volts, and steadies at 9.1 - 9.6 volts, +/- for the 5.64 seconds you cranked the engine.

The MAF sensor shows "0". Confirm the system is programmed to operate in speed-density.

Spark advance shows 7 degrees and injector pulse width is all over the place (11 mSec to 42 mSec) seemingly driven by the MAP sensor value (logical for speed-density).

During this period, was there any sign of ignition? There is one place where the MAP value (103.71 kPa) significantly exceeds barometric pressure (86.37 kPa). Popping back through the intake???? That only happens at the very beginning of cranking it.


PHASE 3

For the balance of the log (42.03 to 113.65 seconds) , the key is on, it has a calculated injector pulse width, but it does not appear you attempted to crank it. All that shows up is the TPS cycling once from 0 to 100%, then quickly closed (73.66 to 75.42 seconds).

Is what I observed above consistent with what you did?

Have you ever tried starting it with a jumper battery? I had long cranking times with my stroker when I first started driving it. I assumed is was the higher compression ratio. Shop that built the engine told me no, it took less torque to turn than the stock engine. I replaced the starter, which apparently was simply drawing too much power, and the engine returned to its stock pattern of firing immediately on the first turn of the key. When I see 7 volts, I doubt the fuel pump or the PCM are very likely to perform the way they are supposed to.

GaryDoug

Seems to crank pretty fast in the video. May be slower during the scan I suppose. Also hear some attempts at firing in the video. We see the cranking rpm on the log so the main Opti output signal is present. Contaminated fuel? Broken or loose rotor?

real82it

Wow, thanks. Spot on, that is what I did. I did not crank for the entire time, just a few seconds.

Tell me what I should do to provide a more useful log for you to analyze. I really appreciate the help.

Put a charger on the battery and then run a log while cranking for 10-15 seconds? I have tried starting it with a fully charged battery previously.

There are intermittent small pops or whoop whoop sounds (can hear in video) once in a while during cranking. That may be what you are observing with the map readings.

real82it

My mechanic thinks water in the fuel. Wants me to completely drain tank and refill. Not sure that explains the car just dieing while I was driving down the road. If that mush water in there, I don't see how it would have rand at all that day.

If rotor was faulty I would not have spark at my plugs, right? (I do have spark at plugs....consistent pulsing spark on #1)

Injuneer

Charge your battery AND jump it from a running vehicle to make sure it's not the low voltage that's causing it not to start. Just start logging 10 seconds before you turn the key to "start", keep it going while you crank for 5 to 10 seconds, then stop logging. There's not a lot to see. Everything that was supposed to be happening was happening, except for the low voltage.

May be pointing to an Opti rotor failure. How many miles on the Opti? Original factory part or aftermarket replacement?