No injector Pulse

Tiny
IMPRESSIONS141
  • MEMBER
  • 1987 CHEVROLET S-10
  • 4 CYL
  • 2WD
  • MANUAL
  • 187,000 MILES
I have a 87 chevy s-10 with the 4-tech 2.5 engine I have spark but no injector pulse I have changed the hall effect switch, ignition module and ecm to no avail, I have also checked my wires going from injector to the ecm and all checked out. Also I have power at injector and plenty of fuel pressure. The only problem I have found is I dont have 10 volts at the p term on the module, but as far as I know that should just not get spark but I am. At this point I am getting frustrated the only thing I can think left to check is for a tach signal getting to the ecm can any one tell me which wire I am looking for and what I should be getting when I check? PLEASE SOMBODY HELP ME!
Tuesday, March 8th, 2011 AT 11:06 PM

16 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
The 2.5 engines had a problem with teh reluctor inside the distributor. They would crack and sometimes run other times not. Check for that, the cure is another distributor. It can also be a problem with a ecm ground. You might try a jumper wire from the negative battery to pcm ground and see if that does anything. If it starts and you get pulses, then it's probably a bad ground.
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Tuesday, March 8th, 2011 AT 11:51 PM
Tiny
IMPRESSIONS141
  • MEMBER
  • 4 POSTS
Actually that was one of my thoughts on the subject and I did supply a good ground to the ecm to no avail.
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Wednesday, March 9th, 2011 AT 3:18 PM
Tiny
IMPRESSIONS141
  • MEMBER
  • 4 POSTS
Well I replaced the distributor and the truck still refuses to start, the only thing I can think of is the new distributor did not come with all new wiring so I had to reuse the few wires inside the distributor as well as what I would call a diode (a small black plastic box with a wire soldered to a ground strap, when I tested this with my dvom I got zero continuity in either direction. I can get a new wire loom with said (diode) but it is almost 250 dollars and am reluctant to replace without confirmation. What are your thoughts on the subject? Also I rechecked the ecm grounds and all three seem to be fine. Do you know which wire at the pcm gets the tach signal and what I should I be reading when I turn over the engine? Please help
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Wednesday, March 9th, 2011 AT 8:30 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
If you knew what type of diode was supposed tobe there you could just go to a place like radio shack and replace the diode. I am sending along pictures and info on how to physically check this system including coil. Hopefully this iwll help find yoru problem. Sometimes the diode should be checked with voltage not ohms.
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Thursday, March 10th, 2011 AT 12:14 AM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
One other thing, here is the only diagram i've found of your system due to age of vehicle. Also make sure when the module is put in the distributor that you use dielectric compound on the metal part that touchs the dist.
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Thursday, March 10th, 2011 AT 12:19 AM
Tiny
BLUEGILL270
  • MEMBER
  • 2 POSTS
  • 1989 CHEVROLET S-10
  • 4 CYL
  • 2WD
  • MANUAL
  • 84,000 MILES
Have fuel fire and vehicle will run if I put the gas straight to throttle body. Injector has power but no pulse. Vehicle ran fine then I decided to tune it up(plugs, wires, cap, rotor) and am experiencing problems. Replace fuel pressure regulator, injector, and computer as well as rewire complete circuit that injector is on. I know that the problem has to do with the computers ability to ground the circuit because before I replaced computer injector was always on if key was on. Now its always off unless I ground it then its always on ( found this when touching a test light to the ground side of injector was just enough to ground for injector to push fuel) I know it has to be a ground somewhere. Does any body know what other circuit could cause the computer to not be able to ground or always ground this.
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Monday, December 2nd, 2019 AT 12:51 PM (Merged)
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
Hello, look for rpm signal. Without rpm signal, I don't believe the computer will ground the injector/s.

The purple wire with white tracer at the distributor, carries the rpm signal to the computer, with the engine cranking. There should be a pulse on that circuit. If you have a dmm that has a duty cycle-- dwell--tach setting, any of these settings will react to a pulse, also a digital logic probe.
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Monday, December 2nd, 2019 AT 12:51 PM (Merged)
Tiny
BLUEGILL270
  • MEMBER
  • 2 POSTS
Thanks that helped alot gave me a place to start that wire had no pulse so I read up and it was either the coil pick up or the hall effect switch (replaced both same time) and solved the problem.
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Monday, December 2nd, 2019 AT 12:51 PM (Merged)
Tiny
BIGBIRDSDIME
  • MEMBER
  • 1 POST
  • CHEVROLET S-10
1989 chevrolet s-10 blazer 4.3 tbi. We have checked everything front to rear and seems to be all ok. Have replaced the control module, fuel pump relay, oil sending unit. We are getting great fuel pressure. We have voltage to the injectors. Truck will run with gas poored in the throttle body so no timing issue. Before we got started on the repair I found a ecm1 fuse blown, so do you think it could possibly be the computer?
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Monday, December 2nd, 2019 AT 12:51 PM (Merged)
Tiny
E40WATER12
  • MECHANIC
  • 522 POSTS
Either youre ECU computer is burnt out, Or u need to replace the fuel, Also could have a short wire soem where. Also could have a fuel pressure regulator no working.
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Monday, December 2nd, 2019 AT 12:51 PM (Merged)
Tiny
1MGMAN
  • MEMBER
  • 4 POSTS
  • 1986 CHEVROLET S-10
  • 4 CYL
  • 2WD
  • MANUAL
  • 89,000 MILES
Injector has the 12v on the red wire on injector, but it never sees the pulsed ground on the blue to fire. Already replaced the ECM and the ignition mod. Very fustrated, usually good with these things. If you intermiantly place a ground on the blue wire you can start and continue run the engine. Why is it not getting it gnd to run. Lost.
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Monday, December 2nd, 2019 AT 12:51 PM (Merged)
Tiny
BMRFIXIT
  • MECHANIC
  • 19,053 POSTS
Check TPS volts
if high ECM is in a flood mode and cuts the injector pulse
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Monday, December 2nd, 2019 AT 12:51 PM (Merged)
Tiny
1MGMAN
  • MEMBER
  • 4 POSTS
Checked TPS voltage good not high. Also, does hall effect turn on injector? From what I read the voltage on pulse wire (middle wire on connector with interruptor in window should read.5 or less, it's reading 5.55dc is this the problem?
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Monday, December 2nd, 2019 AT 12:51 PM (Merged)
Tiny
1MGMAN
  • MEMBER
  • 4 POSTS
Anyone out there with a system like the one I'm working on needs to look at the hall effect switch in the distributor. It's got 12vdc for a supply and a ground on the outside pins. YOU should have no more than.5vdc on middle pin of the switch when interruptor is in aperture. Around 12 when not in aperture. IF more than that, you've found your problem replace it and start it up. HOPE THIS HELPS SOMEONE.I myself could not find this from anyone. It's the first thing you should look at in a situation like this one. Good luck out there. Call me if you need some help with this 937-322-0657
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Monday, December 2nd, 2019 AT 12:51 PM (Merged)
Tiny
DIRTRIDDER4
  • MEMBER
  • 1 POST
  • 1986 CHEVROLET S-10
  • 6 CYL
  • 4WD
  • MANUAL
  • 226,000 MILES
Will not spray fuel/no pulse
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Monday, December 2nd, 2019 AT 12:51 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Check and test the red and white wire at the injector for power if you have it, there's a problem with the injector driver circuit in the computer or its not synchronizing due to ignition reference signal missing
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Monday, December 2nd, 2019 AT 12:51 PM (Merged)

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