injectors not firing.. again

[91dime]

So a while ago my injectors quit firing, after researching, I rebuilt the distributor with a new cap, rotor and ICM. After that everything was running well for a while until it started again. Well I found the clips on the coil were bad and if I unplugged them and plugged them back in, it would fire up no problem. So naturally I got a new harness for it, plugged it in and the injectors won't fire. Not sure where to look next, it's got plenty of fuel pressure going into the TBI. Not sure how replacing 2 plugs would make it not work.

If it's worth anything the injectors are a little wet on the bottom but no drips or spraying. Is it possible for 2 injectors to completely clog at the same time? And how likely is that to happen?

I'm very close to the point of taking all this efi stuff out and throwing a carb on the truck. Iv spent so much time tinkering with this thing just to get it to run decent it's making me bitter. As soon as one thing is fixed something else starts acting up making it a pain to attempt to tune. Sorry for the rant.

Sorry for typos or weird sentence stuff, I'm typing this out on my Android.

[jim_in_dorris]

Ohm out the new harness, have to guess you have an open circuit.

[91dime]

I should have said pigtails or whatever you want to call it. It's just the 2 new plugs that go to the coil with wires about 6 inches long I had to connect to the existing harness, I tested them with a multi meter and the wires seem to test fine, voltage is going to the coil at the very least. And the one wire that comes from the dizzy to the coil that I can take off, test with no resistance so the dizzy is connected to the coil no problem. I even tried another coil I had laying around and still no luck. I made sure the crimps were strong. To afraid to have soldered wires around an engine block, to many heat cycles may make the solder brittle.

[jim_in_dorris]

next test is to find a noid light to see if the ECM is trying to fire the injectors. I just had to replace the connectors to my injectors, they were old and broken. As I drove down the road, they would work loose and the truck would stall. I would get out, plug them back on the injector, and could drive another couple of miles. Rinse and repeat. It got old fast, and the temporary fix only worked for a couple of months.

[91dime]

I have not had the chance to get a noid light yet but I did three other test.
First, I used a 9v battery on the injectors and both sprayed fuel no problem with the fuel pump running. So that must mean both injectors are fine.

Second, I tested the positive pins on the injector plugs, both read the same voltage tested at the battery.

Third, I tested the wires that go to the PCM to direct ground and no short. So next I tested the wire at each end to make sure they arn't broken and both test with 2 ohm. Since both read the same I would like to assume they are both fine.

So now I know the plugs are properly connected to the PCM and a 12V source plus the fact both injectors fire when using a 9V battery. Does this mean the PCM may have taken a crap? Or did the new module I put in the distributor fail already? Should I still pick up a noid light knowing now that both injectors work under power and the voltages and wires are good?

[EDZIP]

Those noid lights are a must...the only way to determine if your ecm is sending the ground signal since you know you have 12v to each injector. I think even Harbor Freight sells them.

I'm sure you have tried spraying some gas into the throttle body to see if it runs.

[91dime]

I actually have not tested if it will run with fuel or not.

As far as the noid light, correct me if im wrong, but if the noid light flashes properly when turning over, that means the PCM is grounding properly correct? Now if its grounding properly to flash the light, why would it not pulse the injector? Im not trying to question your intelligence or be rude in any way, Im just a bit confused.

[EDZIP]

I actually have not tested if it will run with fuel or not.

As far as the noid light, correct me if im wrong, but if the noid light flashes properly when turning over, that means the PCM is grounding properly correct? Now if its grounding properly to flash the light, why would it not pulse the injector? Im not trying to question your intelligence or be rude in any way, Im just a bit confused.

The noid will flash as you attempt to start the car, which means you have both power (12v we hope) and the signal ground from the ECM. If you are working on a TBI engine you should be able to see the injectors pumping fuel, if it's a TPI engine obviously you can't.

I'd get some gas or starting fluid and have someone turn it over while you supply fuel...if it starts you know you have a fuel problem and not electrical.

One problem I recently ran into was a plugged return fuel line...pressure was so high the injectors wouldn't open. Squirted some fuel in the throttle body and it fired..so I knew it was a fuel problem

[91dime]

I failed to mention this is a TBI, Its a 7427 computer controlling it all. I recently redid the fuel system to include metal lines and fittings on most all of the fuel system and an adjustable FPR set at 20 PSI to get it to support more power. I have everything set up in the BIN to accommodate the new upgrade. It ran great previously. I also have a gauge rite before the tbi to monitor pressure and it never goes over 20 so i wouldnt think the fuel system has a blockage. I also confirmed that both injectors do spray properly when connected to power and they do receive the proper 12V of power.

I hate to think but how likely is it that the 7427s injector driver has failed me?

Tomorrow i will manually pulse the injectors to see if it actually fire. All of the ignition stuff is new except for the coil.

[EDZIP]

I failed to mention this is a TBI, Its a 7427 computer controlling it all. I recently redid the fuel system to include metal lines and fittings on most all of the fuel system and an adjustable FPR set at 20 PSI to get it to support more power. I have everything set up in the BIN to accommodate the new upgrade. It ran great previously. I also have a gauge rite before the tbi to monitor pressure and it never goes over 20 so i wouldnt think the fuel system has a blockage. I also confirmed that both injectors do spray properly when connected to power and they do receive the proper 12V of power.

I hate to think but how likely is it that the 7427s injector driver has failed me?

Tomorrow i will manually pulse the injectors to see if it actually fire. All of the ignition stuff is new except for the coil.

You have done everything except give it fuel manually, if it fires with fuel manually sprayed into the throttle body I would also do a fuel sample...in case you have bad (water) fuel. Just the basics first.

[91dime]

So if it does fire up with fuel added manually, where do I look next?

[EDZIP]

So if it does fire up with fuel added manually, where do I look next?

Then you know it's a fuel related problem since you have spark, compression, ignition etc.

That's why I keep extra ecms and throttle bodies on the shelf..it's a lot faster to just swap with a known good component.

Make sure you have "spark at the plugs" ..I know you replaced the ICM...but those GM trucks are known for burning up ignition control modules...I keep a few of them on hand for that reason. If you don't have spark and wind up replacing the ICM...remember the engine might be full of raw gasoline from trying to start it...with spark your muffler could go boom.

Autozone can test the ICM for free...but they need to run the test at least 3 times and make sure you use thermo lube under the ICM to transfer the heat or it will burn up.

[91dime]

I have another ICM that Hopefully works along with thermal compound I use to build computers. Is it the heat that kills them or other factors along with heat?

[EDZIP]

I have another ICM that Hopefully works along with thermal compound I use to build computers. Is it the heat that kills them or other factors along with heat?

Apparently heat is the major factor..but product quality is also. If you have a module made by RichPorter...I'd be looking for an ACDelco.

[91dime]

It's an acdelco I bought from Rock auto, it does have a warranty option so if it's bad, I'll be using that.