'91 S-10 Blazer Fuel pressure good but injectors wont squirt

[KroniK18]

Hey guys,

I just acquired a 1991 Chevrolet S-10 Blazer with a 4.3L V6. I Picked it up at an impound lot auction so I really have no clue as to what the history is of this car or what any of the symptoms were before this car stopped starting.

Here are the current symptoms:

-Engine cranks but wont fire
-If starter fluid is sprayed in the TBI then the engine will fire.

Here is what I have deduced from my own troubleshooting and what repairs I have made so far:

-Fuel pressure into the TBI is at about 10psi which seems normal according to the manual
- I replaced the fuel pressure regulator spring and diaphragm (the spring was broken into 3 pieces)
- When I put the TBI back together, the injectors squirted fuel ONCE and then quit.
-I then took it back apart, fiddled with it and put it back together, again when I cranked it, the injector squirted ONCE and then stopped.

My next idea was to try replacing the filter on the end of the injector, or have the computer looked at. otherwise I am at a loss. Someone told me that I should look at the EGR valve and make sure there is nothing plugging that up.

Thank you for taking time to help!! I hope I have given sufficient information in order for you to have some Ideas of where I can go from here. I am happy to answer any questions which may help you understand the trouble I am experiencing.

Currently feeling like Him --->

[MT-2500]

Originally Posted by KroniK18

Hey guys,

I just acquired a 1991 Chevrolet S-10 Blazer with a 4.3L V6. I Picked it up at an impound lot auction so I really have no clue as to what the history is of this car or what any of the symptoms were before this car stopped starting.

Here are the current symptoms:

-Engine cranks but wont fire
-If starter fluid is sprayed in the TBI then the engine will fire.

Here is what I have deduced from my own troubleshooting and what repairs I have made so far:

-Fuel pressure into the TBI is at about 10psi which seems normal according to the manual
- I replaced the fuel pressure regulator spring and diaphragm (the spring was broken into 3 pieces)
- When I put the TBI back together, the injectors squirted fuel ONCE and then quit.
-I then took it back apart, fiddled with it and put it back together, again when I cranked it, the injector squirted ONCE and then stopped.

My next idea was to try replacing the filter on the end of the injector, or have the computer looked at. otherwise I am at a loss. Someone told me that I should look at the EGR valve and make sure there is nothing plugging that up.

Thank you for taking time to help!! I hope I have given sufficient information in order for you to have some Ideas of where I can go from here. I am happy to answer any questions which may help you understand the trouble I am experiencing.

Currently feeling like Him --->

Ign module and pickup coil has to be good to triger pcm injector pulse.

For injector to squirt you have to have fuel pressure to them and 12 volts on positive side and a injector ground pulse on neg side.
Check for injector pulse when engine cranking.

Is the pcm pulsing injectors when cranking engine?

The pickup module has to triger ign spark and the pcm for the pcm to pulse injectors.

Check dist for good hot spark to all plugs when cranking engine.

If good hot ign spark then check computer for lose of injector pulse.

[KroniK18]

Originally Posted by MT-2500

Ign module and pickup coil has to be good to triger pcm injector pulse.

For injector to squirt you have to have fuel pressure to them and 12 volts on positive side and a injector ground pulse on neg side.
Check for injector pulse when engine cranking.

Is the pcm pulsing injectors when cranking engine?

The pickup module has to triger ign spark and the pcm for the pcm to pulse injectors.

Check dist for good hot spark to all plugs when cranking engine.

If good hot ign spark then check computer for lose of injector pulse.

I Have Just tested if the PCM is Pulsing the injectors, and it is NOT.
I Do Have enough fuel pressure, and the engine will fire when starting fluid is added, so the spark/distributor should be fine.

Now that I know the reason for why the injectors are not pulsing, How do I figure out why the PCM is not pulsing the ground on the injector?

thanks for your help so far!!!

[MT-2500]

Originally Posted by KroniK18

I Have Just tested if the PCM is Pulsing the injectors, and it is NOT.
I Do Have enough fuel pressure, and the engine will fire when starting fluid is added, so the spark/distributor should be fine.

Now that I know the reason for why the injectors are not pulsing, How do I figure out why the PCM is not pulsing the ground on the injector?

thanks for your help so far!!!

Starting fluid is not a good test for good ign.
It can fire a engine without ign spark and in some cases blow the dip stick and valve covers threw the hood and or the oil pan off the engine or blow the starting fluid can up in your hand.
Not good on hands and eyes and any persons head under the hood.
Only use carb spray or just a little gas in a little container down throttle body gas.
Do not use a 5 gallon can of gas.
A small squirt 1/2 pint container is a lot safer and will do the job.
For the ign test.
Use a spark tester to test for good hot blue sprk to all plugs.
Watch for a steady spark while cranking engine.

If you have good steady spark and all wiring power and ground and ign wiring to computer is good and no injector ground pulse.
Also the PCM has to have a RPM signal from ign. system to triger injector.



The only test for a bad PCM is sometimes the tap/twist test or the best test is installing a known good computer.

Let us know how it goes.

[KroniK18]

Originally Posted by MT-2500

Starting fluid is not a good test for good ign.
It can fire a engine without ign spark and in some cases blow the dip stick and valve covers threw the hood and or the oil pan off the engine or blow the starting fluid can up in your hand.
Not good on hands and eyes and any persons head under the hood.
Only use carb spray or just a little gas in a little container down throttle body gas.
Do not use a 5 gallon can of gas.
A small squirt 1/2 pint container is a lot safer and will do the job.
For the ign test.
Use a spark tester to test for good hot blue sprk to all plugs.
Watch for a steady spark while cranking engine.

If you have good steady spark and all wiring power and ground and ign wiring to computer is good and no injector ground pulse.
Also the PCM has to have a RPM signal from ign. system to triger injector.



The only test for a bad PCM is sometimes the tap/twist test or the best test is installing a known good computer.

Let us know how it goes.

How could I test for the RPM signal? and Is there some place I could go to find what I should expect to find (voltage and ohm wise) across different pins on the PCM? I dont know where to find a manual to troubleshoot inputs and outputs from the PCM.

I am going to try using a 3.9K resistor across two test terminals according to THIS web page. It should put the PCM into "Backup Mode" and only uses the tps, engine speed, and cst to activate the injectors. I will reply later with my results

[KroniK18]

Well, using the 3.9K resistor did nothing. So I'm back to where I started. I have a relative with an S-10 pickup, same vintage, which I might try to use to swap the PCM out for a known good one. I do Know about swapping the ROM so I will be sure to do that, however after this point, I really don't know what else I could do.

[MT-2500]

Originally Posted by KroniK18

Well, using the 3.9K resistor did nothing. So I'm back to where I started. I have a relative with an S-10 pickup, same vintage, which I might try to use to swap the PCM out for a known good one. I do Know about swapping the ROM so I will be sure to do that, however after this point, I really don't know what else I could do.

Factory repair manual or All Data DIY sub have pin out charts.
But they do not always show problem.



First step is confirm good hot blue spark to all spark plugs engine cranking.
If good spark move on to wiring/plugin and pcm problem.

Is it setting any codes?

A engine scanner will read out RPM siginal to computer and also injector pulse.

A good PVM tap/twist a lot of times will show bad/cracked pcm circuit board.
Good spark to all plugs and no injector pulse points to dead PCM/computer.

A computer swap out is next step.

Salvage yard have used or parts places also have rebuilt computers.
Rebuilt ones can be bought for around 75-85 USA dollars.
Used are sometimes a dime a dozen.
Just be sure to replace with same part no.
Let us know how it goes.
Good luck

[KroniK18]

Originally Posted by MT-2500

Factory repair manual or All Data DIY sub have pin out charts.
But they do not always show problem.



First step is confirm good hot blue spark to all spark plugs engine cranking.
If good spark move on to wiring/plugin and pcm problem.

Is it setting any codes?

A engine scanner will read out RPM siginal to computer and also injector pulse.

A good PVM tap/twist a lot of times will show bad/cracked pcm circuit board.
Good spark to all plugs and no injector pulse points to dead PCM/computer.

A computer swap out is next step.

Salvage yard have used or parts places also have rebuilt computers.
Rebuilt ones can be bought for around 75-85 USA dollars.
Used are sometimes a dime a dozen.
Just be sure to replace with same part no.
Let us know how it goes.
Good luck

Well I think I figured it out! One of my family members owns a 91 chevy s-10 pickup with the exact same engine in it. So I tried swapping the computers (did nothing) and I finally tried swapping the distributor, and that worked!! The injectors started pulsing! So I will get a distributor tomorrow, and try and get it running. I will keep you posted on how it runs.

[MT-2500]

Originally Posted by KroniK18

Well I think I figured it out! One of my family members owns a 91 chevy s-10 pickup with the exact same engine in it. So I tried swapping the computers (did nothing) and I finally tried swapping the distributor, and that worked!! The injectors started pulsing! So I will get a distributor tomorrow, and try and get it running. I will keep you posted on how it runs.

As in post no 2.
Ign module and pickup coil has to be good to triger pcm injector pulse.