bigjay89gta

iTrader: (5)

Car wont start.

Fuel pressure to rails at 48psi, clean spark.

Datalog shows No injector pulse width.

Temp is 52 degress.
TPS is .55 volts...
MAF showing 5grams..

What causes no Injector Pulswidth?

Of course NO TCs

vetteoz

iTrader: (13)

Assuming it is cranking over ????

Inj fuses blown?
A bad injector (low Ohms or shorted ) will shut down inj pulse.
No ref signal from dist
No input from oil pressure switch to ECM
VATS module faulty on injector signal to ECM

http://www.corvettebuyers.com/c4vettes/l98.htm

Davidgou

iTrader: (2)

Sounds like a VATS problem. Do you know if you have VATS?

bigjay89gta

iTrader: (5)

Yes car is cranking...full battery. Full spark and plenty of fuel pressure. Vats is bypassed as well as disabled in Chip. All fuses checked and are functioning properly at least all the ones in the fuse block under driver side dash.

Car will start with Starting Fluid, but will not stay running. So I believe that kills all the Cold Start Pulsewidth problems.

Regarding oil pressure. with continuous cranking Oil pressure on Gauge shows 30psi. Is there something else that communicates with the ECM regarding Oil pressure? How can I check this.

I am guessing the distributor Ref signal comes from the ICM(ignition control module). I am going to replace it anyway, have had bad luck with them in the past. Rebuilt the distributor 2 years ago...new everything. Car still had intermitten starting issues after the distributor rebuild.

Injectors where replaced recently less the 4 months ago with Bosch 28lbs, but I will check them as well.

Car also has a custom tuned chip. I have AutoProm and TunerPro RT.

If there is anything else I can look at in TunerPro datalog. Let me know and I will check it out.

I will check those things out Monday. And let you know whats up.

Thanks for all the help.

vetteoz

iTrader: (13)

OP switch that runs the fuel pump also send signal to ECM.
If ECM doesn't see this input (fuel pump signal ) during cranking ( only ) it won't pulse the injectors

Rod Behring

The fuel pump is working if you have 48 psi at the rail. I think you are on the right track with the ICM. Or it could be the EST wiring to the ECM. Maybe the ECM is bad?

vetteoz

iTrader: (13)

Fuel pump primes ( through relay ) , "key on" which gives you pressure at rail.

Doesn't mean OP switch is working ( powers pump direct from switch , see diagram above )
ECM needs to see pump run from OP switch before it will pulse the injectors

speedlimit96

i wouldnt say its your icm, b/c that has nothign to do with your injectors pulsing, you said you replaced fuel injectors, did you replace fuel rail as well maybe something in that is bad, or maybe wiring to the injectors. i know i just had a problem with mine dying once i put it in drive or when slowing down to a stop sign it would die out and it ended up being my injectors!!

Davidgou

iTrader: (2)

But he already replaced the fuel injectors about 4 months ago, he said. What does the fuel rail have to do with anything?

bigjay89gta

iTrader: (5)

ECM is good since I can Datalog and the car will run on starting fluid.

The problem is that the Injectors arent opening and closing. Fuel Pump does prime.
The car ran great after injector replacement. I replaced injectors because I tried everything else to get rid of the Intermitten NO start.

Will take extra wiring to see if Maybe I can bypass the OP switch. Also anyone know which wire sends Reference reference signal from the Distributor to the ECM so the ECM knows to Start fireing injectors?

vetteoz

iTrader: (13)

On dist plug
Purple / white is ref pulse
Red / blk is ref pulse ground
White is spark timing
Tan / blk is bypass

See
http://www.austinthirdgen.org/mkport...ine_wiring.gif

vetteoz

iTrader: (13)

Really

Maybe you should read this then
Especially the part on ECM Reaction:

http://www.corvettebuyers.com/c4vettes/l98.htm

KNBlazer

I say it's the ICM... or it could be a break in the harness... it could also be a bad driver in the ECM, right?

speedlimit96

i just read that link on no start problem and it doesnt even mention the ICM(ignition control module) it mentions the ECM(engine control module). i know the ecm has alot to do with the injectors pulsing, the ICM does not though it has to do with the spark of the spark plugs. are you starting to see the difference now.

Rod Behring

My car still ran with a bad oil pressure switch. The ECM will still (through relay) operate the fuel fuel pump without OPS.

I still think ICM or EST wiring.

vetteoz

iTrader: (13)

On TPI engines it is referred to as the ESC (Electronic Spark Control ) module
ICM is on LT1 engines

On the early TPI cars with the standalone ESC module you could disconnect it and the engine would still start and run fine; all it would do is throw a code because the ESC only interfaces with the knock sensor and adjust spark if knock is seen

The EST (electronic spark timing) module is in the distributor

vetteoz

iTrader: (13)

Of course, but the ECM needs to see the OP switch operate while cranking only.It serves to show ECM that the engine has oil pressure
After engine starts ,ECM doesn't take any input from OP switch

Rod Behring

I didn't know the ECM needs a signal from the OPS to start.

I thought the fuel pump circuit could be completed by the fuel pump relay, or as a back up in case the relay fails, the OPS.

Of course the OPS also send signal to the gauge. I think he said the gauge showed pressure though.

bigjay89gta

iTrader: (5)

Vetteoz....so after the car starts, it no longer needs input from the OP switch?

vetteoz

iTrader: (13)

Exactly
is only referenced during cranking

While the OP switch is primarily there to power the pump up should the pump relay fail ,it also serves a dual purpose by supplying 12 V to the ECM to indicate that engine has oil pressure.
When the ECM " sees" the engine has OP while cranking it then pulses the injectors ( so long as it is also seeing the dist ref pulse)
Many think guys the switch is there as a safety cut off should OP drop but this incorrect
Once engine is running you could unplug the switch and engine would continue to run ( assuming pump relay is working )

Might get so tips here
http://forums.corvetteforum.com/c4-t...tor-pulse.html

mlynch001

Get a noid light. Unplug a convenient injector plug in, Unplug the distributor 4P connector, turn on the key, does the noid light come on? If the Noid light is on with the key, then the fuses and wiring are intact, if NOT then you got some issues with the harness/fuses./ECM. If the noid light comes on with the key, connect a 12V test light to the battery and quickly touch the test light probe to the purple/white wire (Circuit 430) in the HARNESS side of the distributor plug. injectors should pulse and the noid light should flash as you "tickle" that wire with the 12 V test light ,you can usually HEAR the injectors click when you do this test as well. DO NOT leave the 12V attached, just quickly touch the terminal. If not, you have an open in Circuit 430, open fuses, bad grounds, bad ECM etc. If you get a reaction at the injectors and noid light from this test, then you have a bad ICM or bad connection inside the distributor. You could also have a bad TPS. If the TPS is reading WOT all the time, you will be in "clear flood" mode where the injectors will not pulse while cranking.

BTW
The OP Switch has NOTHING to do with the injector pulse, it is a backup 12V fuel pump circuit only! The 12V flows from the starter relay battery post fusable link to circuit 340 AND the Fuel Pump relay AND to the Oil pressure switch then out to the fuel pump as well as to circuit 120 on B2. This is a parallel circuit. The oil pressure switch is a "Fail safe" for the fuel pump relay in the event that the relay fails. The ECM MUST see 12V power from Either the Pump Relay OR the Oil Pressure switch (or both) or it will not allow the engine to start. The ONLY way that this circuit would stop the injectors would be IF the Oil pressure switch AND the Fuel Pump relay have BOTH failed! Circuit 120 must "see" 12V from the fuel pump relay AND/OR the Oil Pressure switch. If the fuel pump relay fails, then the Oil Pressure switch is the default 12V source for circuit 120 AND the Fuel Pump. If the FP relay fails, then the FP will not run until the oil pressure rises and the switch closes to supply 12 V to the fuel pump and Circuit 120. As long as the fuel pump relay remains functional, the OP switch is redundant. Circuit 120 is also a voltage reference line for the ECM that allows the ECM to compensate for system voltage fluctuations which affect fuel pressure and therefore the fuel mixture. If the ECM senses low voltage Under 2.0V over 1.5 second from the last reference pulse at circuit 120 and pin B2 it will set a code 54. this usually means that the fuel pump relay has failed.

vetteoz

iTrader: (13)

But as the relay does not operate again (after initial prime ; key on ) until the ECM sees the dist ref signal and input on # 120 the ECM is dependent on the voltage from the OP switch?

Rod Behring

We know the fuel pump is priming so the fuel pump relay must be working, right?

After it primes the ECM needs the 12v signal to run the pump, right?

If it is showing 48 psi constantly while cranking than the ECM must be seeing the 12v in FP circuit and running the pump after priming

bigjay89gta

iTrader: (5)

Update replaced the ICM...no start.

TPS is fine according to the Datalog. Shows TPS at .55volts at start up. Getting a Noid Light and a multimeter to test injectors. Is there a way I can test the wiring INside the car.

Like can I disconnect the ECM and probe the proper PIN to see if ecm is seeing Ref pulse?

Or do I need the ECM connected thanks.

3rd gen Will

iTrader: (8)

I'd disconnect the connector from the distributor and the ECM and Ohm the wire, make sure you have continuity to make sure you don't have a break in the wire.

here is my thread, that wire being broken was my problem.
https://www.thirdgen.org/forums/tech...rk-doesnt.html

mlynch001

You should be able to unplug the ECM connector and check for the pulse at the ECM Plug. The Distributor pulse to ECM on Circuit #430 in independent of the ECM. Circuit 430 should be found at pin D8 on the 7730 ECM. Wire color at the ECM plug should be Purple/White. When you crank the engine, you should get a pulse at that wire to ground. You can also check the continuity of that wire with an Digital MultiMeter. I would check for opens, high resistance and shorts to ground in that wire.

KNBlazer

would a bad pickup coil cause a no pulse condition? or does it only control spark?

bigjay89gta

iTrader: (5)

DId a check with Noid Light result was nothing. Checked Wiring it is good, replaced all fuses just in case. Swapped in a Working ECM and it fired right up.

I didn't think a fired ECM, would datalog properly or allow the car to actually run on Starting fluid. Got a new ECM and installed with original Tune. Everything works...although it is running rich due to injectors .

Thanks for all the help guys.

Jason

mlynch001

Yes, the ignition is partially separate from the ECM. The ECM Does control the spark advance, but the car will start and run with no spark advance if you feed fuel to it. Glad you got it going!

bigjay89gta

iTrader: (5)

I also appreciate all the info vetteoz put out there.

I enjoy learning step by step how stuff works. Might get my electrical engineering degree and go into Automotive Control systems, since I enjoy it so much.

Thanks again to all who helped.

InjectorsPlus

iTrader: (1)

Anyone ever see an injector driver go bad? Just had it happen in a BS3 for a customer....

Any way to check that?