95 S10 4.3 No injector pulse Help Please !!!

Hey Friends; I'm helping a young couple with a problem.Their 95 S10 4.3 has been getting harder and harder to start and now it won't start at all.Well I checked the fire,it looked fine.Pulled the air cleaner lid and no injector pulse.I made a relay jumper for the fuel pump that was replaced a year ago and it's humming right along.I pulled the 4 wire plug from the ignition module and powered up the IC hi reference wire (purple/white) to the computer with a testlight connected to the battery positive post and NO PULSE.I checked the four wires from the module to the PCM and the purple/white was open so I ran a jumper to both ends and when I power that wire with a test light now (purple/white),the injectors will pulse with a fuel spray but still NO PULSE while cranking.That lead me to believe the problem was in the distributor.I tested the module and it showed to be fine but I put on a new one anyway,still NO PULSE.I pulled the distributor out and replaced the pickup coil and it didn't look very healthy at all.I examined the reluctor wheel as best I could.It looks fine to me.The shaft isn't loose in the distributor and the gear looks normal.I tested the distributor with my module tester attached and the reference light flashed up there as bright as the tach light on the tester. I was sure the pickup coil must be the culprit.Well I went to their home tonight and dropped in the distributor and dog-gone-it, NO PULSE.What am I overlooking here.Would someone "PLEASE HELP ME".Thanks R.D.

Do you have 12 volts to positive injector side?
Confirm good fuel pressure.
Check for good hot blue spark to all plugs.
Check for injector pulse with a injector pulse noid light.

The PCM uses groun to neg side to pulse injector?
Is pcm pulsing ground?

Hi there MT.I didn't want to bore you with the entire series of events so I left out what I felt wasn't needed to say.Yes I used a noid light first and there is NO PULSE.I have 12 volts to both injectors.I have good spark from the coil wire and the #1 plug.I read a post on Just Answers from a technician named Frank back on August 6 2006 and he spelled it out this way. "take a test light connected to battery positive and touch the purple/white wire at the harness connector side of the ignition module.If the injectors pulse with a SPRAY OF FUEL each time you touch the terminal,then the problem is in the distributor".Well I have a spray with a test light but nothing while cranking.That to me would indicate 12 volts to the injectors,fuel pressure and grounding to the injectors from the ECM. Now I've looked the distributor over and have put in a pickup coil and module.I've bypassed the oil pressure switch and the fuel pump relay and I have 12 volts to the gray wires in the red and blue plug of the ECM.Many time folks make things a lot more complicated than they really are.That's why I tell them to do the basic things first.I checked the fuses.Checked for voltage to the injectors.It will run if you nurse gas down its throat.I know there's a simple answer to why I have NO PULSE CRANKING. I'm just trying to think through this problem and need a little help.

Hi there MT.I didn't want to bore you with the entire series of events so I left out what I felt wasn't needed to say.Yes I used a noid light first and there is NO PULSE.I have 12 volts to both injectors.I have good spark from the coil wire and the #1 plug.I read a post on Just Answers from a technician named Frank back on August 6 2006 and he spelled it out this way. "take a test light connected to battery positive and touch the purple/white wire at the harness connector side of the ignition module.If the injectors pulse with a SPRAY OF FUEL each time you touch the terminal,then the problem is in the distributor".Well I have a spray with a test light but nothing while cranking.That to me would indicate 12 volts to the injectors,fuel pressure and grounding to the injectors from the ECM. Now I've looked the distributor over and have put in a pickup coil and module.I've bypassed the oil pressure switch and the fuel pump relay and I have 12 volts to the gray wires in the red and blue plug of the ECM.Many time folks make things a lot more complicated than they really are.That's why I tell them to do the basic things first.I checked the fuses.Checked for voltage to the injectors.It will run if you nurse gas down its throat.I know there's a simple answer to why I have NO PULSE CRANKING. I'm just trying to think through this problem and need a little help.

What engine code?
Pcm inside cab or VCM on fender?

Flat top dist or old style?

Old school if computer is getting all powerr and ground and signals and no injector pulse = bad computer.

Is the coimputer getting crank RPM signal?
If the computer is getting rpm signal and you have good spark the computer should be puting out injector pulse.

Check all wiring and power and ground and plugin to computer.
Run a pin out test on it.

MT;This rig has a Z motor with vertical towers on the cap.The computer is inside under the glove box.I installed a rebuilt computer on it this morning and still no pulse.I'll do some more testing on it tomorrow night.I know proper testing is the answer to my problem,I'm just trying to figure what to test next.Thank you for your interest and your time.R.D.

MT;This rig has a Z motor with vertical towers on the cap.The computer is inside under the glove box.I installed a rebuilt computer on it this morning and still no pulse.I'll do some more testing on it tomorrow night.I know proper testing is the answer to my problem,I'm just trying to figure what to test next.Thank you for your interest and your time.R.D.

Go back over all wiring to dist pcm and plugin's and power and ground to the computer.

Is the dist feeding rpm signal to pcm?
Is the pcm putting out any injector pulse?
Does TPS sensor check out good.
Any anti theft stuff that could be shutting off injector pulse?

Did you switch out prom from old to new pcm?

Any codes stored in PCM?

Can anyone tell me the voltage output of the ignition module at the "R",purple/white,high reference terminal.I'm getting .390.That's less than 4 tenths of a volt.That can't be good.I have two Chilton manuals here and I can't find any reference to that.When I put 12 volts to that wire my injectors will open and I get a spray of fuel.I'm not getting enough voltage to that wire from the module for some reason with a new module and a pickup coil.Thanks RD

Well I just finished setting up the distributor on my test bench with an ignition coil and a 12 volt battery and with a drill spinning the distributor I get 2.09 volts at the R terminal of the module.Is that enough voltage to make my computer pulse the injectors? I've proven 12 volts will.

....It will run if you nurse gas down its throat.....

If that's the case, the PCM is seeing a pulse and the ignition system is working. Check the fuel pressure: key on engine off, fuel pump running, pressure should be 9psi to 13psi for the "Z" TBI engine.

If that's the case, the PCM is seeing a pulse and the ignition system is working.

My question was,will my PCM pulse at 2.09 volts from the R terminal of the module and your apparently saying that it will since you said the PCM is seeing a pulse.Well why will it pulse when I put 12 volts to it and not at 2.09 volts? My pump is running and when I put 12 volts to the R terminal I GET A SPRAY OF FUEL but it WILL NOT PULSE from the distributor.What I trying to find out is what the manufacturer says the output should be out of the module.

The pick up coil in the distributor generates AC voltage, (measured in millivolts), when the distributor turns. The AC voltage is sent through the ignition module to the PCM for processing. The PCM adjusts the ignition timing and sends a modified DC voltage signal to the ignition module. The ignition module sends a pulsed ground to the ignition coil and the ignition coil fires.

Battery voltage is applied to the injectors when the ignition is in the START or RUN positions. The PCM uses the data from the pick up coil to determine when to fire the injectors. The PCM applies a pulsed ground directly to the injectors which completes the circuit, and the injectors open.

4 terminal connector on the ignition module:

G = Ignition Control low voltage reference (from ignition module to PCM)
B = Timing bypass (from PCM to ignition module during closed loop operation)
R = Ignition Control high voltage reference (from ignition module to PCM)
E = Ignition Control (from PCM to ignition module during open loop operation)

The two terminal connector on the ignition module:

+ = Battery voltage when ignition is in RUN or START position
C = Supplies pulsed ground to ignition coil

To check the pick up coil:
1). Connect an ohmmeter to each terminal of the pick-up coil connector or wire and ground (one terminal at a time). The ohmmeter should indicate infinite resistance. If it doesn't, the pick-up coil is defective.

2). Connect the ohmmeter between both terminals or wires of the pick-up coil connector. The ohmmeter should indicate one steady value within the 500 to 1500 ohm range as the wires are flexed. If it doesn't, the pick-up coil is defective.

If the pick-up coil fails either test. replace it.



Hope this helps.

WELL !!!!!! I got it fixed.It turned out to be simple,naturally,after I figured out what was wrong.This pickup was equipped for the USAF with CNG,compressed natural gas.I asked the owner how it would convert over and he said he would get out and turn a valve on the tank while the engine was running and that's all.No switches or buttons to push ,just the valve.I knew the system would have to disable the injectors,but how? Well since we had no injector pulse I had a hunch that the issue was due to the CNG system.But where on Gods green earth would you get information on a system like that?
I first tried the trick that an advisor named Frank on Just Answers told."Put a test light from the battery positive to the purple/white wire on the module plug and if the injectors pulse then the problem is in the ignition".That wasn't exactly true in this case.My purple/white wire was open from the module R terminal to the computer A4 on the Red plug so I ran a jumper wire to both ends and then the injectors would pulse with the testlight but not while cranking.I started looking over the ignition system,testing fuses checking voltages,all with no success.I had the desired 1.2 to 1.6 volts while cranking at the end of the jumper wire from the module but when I connected it to A4 at the computer,my voltage would drop to .50 to .69 volts while cranking.After two weeks in the evenings of testing and out of ideas,I cut the purple/white wire off at the computer and connected the jumper to the computer to see what my voltage reading would be and it STARTED right up.Everybody wants to say now that the purple/white wire was grounded/shorted,whatever.I dont think so.I believe there's a pressure switch somewhere in the CNG system that opens that wire to kill the injector pulse but what I don't understand was why it would kill half of my voltage to the computer.I think I will go back and cut the wire loose at the module end too just in case.Boy what a nightmare this has been.Many thanks go out to the Old Master,MT2500 and a techician named Larry from Standard Motor Products.R.D.

Now that's not something you see everyday...thank God! Glad you finally found it.

Now that's not something you see everyday...thank God! Glad you finally found it.

Thanks for posting back how it went.
Glad you stayed with it and found the problem.
Good Luck