Weak Injector Pulse

[Rally Smith]

Hello all,
On my 95 GMC K1500 350 Auto TBI, the driver side injector is not spraying as well as the other and has a weak ground signal coming from the ECM to fire it. I swapped the injector connectors and it follows the one injector harness. The green wire coming out of the ECM for the Ground Signal is week at the ECM plug. I have taken some ground straps off of the fire wall and frame rail in engine compartment to clean up and no difference. Anybody have any other ideas? I have also tried unplugging the TPS sensor wire for whatever reason that I read on other forums that I have been researching. I have seen where other people have had the exact problem but there is never a conclusion to the problem. IF I need a new ECM is there a way to convert it into a ECM that I can put a EBL into it?

Thanks,

R.S.

[PJG1173]

have you checked resistance on the wire between the injector and computer?

[Rally Smith]

have you checked resistance on the wire between the injector and computer?

Well, I checked and it showed that there were no breaks in the wire. I don't think there should be resistance should there be?
I got the same dim test light when cycling at the ECM as at the injector harness.

[fastacton]

If the wire is good, you might have an ECM that's going bad. Do you have one you can swap out to see what happens?

[Rally Smith]

If the wire is good, you might have an ECM that's going bad. Do you have one you can swap out to see what happens?


I do have another ECM out of another 95. It does not have the same Prom ID # though. I tried it before and it didn't seem to make any difference.
Makes me think that there is a problem somewhere that supplies the ECM. I suppose I could have picked up a bad ECM at the yard as well...

Thanks,

[PJG1173]

Well, I checked and it showed that there were no breaks in the wire. I don't think there should be resistance should there be?
I got the same dim test light when cycling at the ECM as at the injector harness.

there will be some resistance. since you are getting a signal to the injector it is assumed that there are no breaks in the wire. I wouldn't just check for continuity, if you compare resistance of the good injector's wire between the computer and injector to the one you are getting a weak signal on you can rule out the wire itself. also have you tested voltage on the B+ side of the injector?

[Rally Smith]

there will be some resistance. since you are getting a signal to the injector it is assumed that there are no breaks in the wire. I wouldn't just check for continuity, if you compare resistance of the good injector's wire between the computer and injector to the one you are getting a weak signal on you can rule out the wire itself. also have you tested voltage on the B+ side of the injector?

I have checked the positive side of the injector harness on both sides and they are the same. (12v) Not sure that will make a difference because I can see the weak signal at the ECM Plug. Not sure if I can attach a short video or not but I'm going to try to show the issue I see.

Thanks,

[delcowizzid]

Put down the test light it shouldn't be used for testing anything Efi forget you own it unless it's an Efi specific led version or a noid light for testing injector drives.unplug injectors and ecu and battery test resistance of the 12v feed from injector power relay to both injectors separately.then test resistance of the feeds from injectors to ecu

[Rally Smith]

I can't upload it. It's a .mov file and that won't work. Basically what it shows is, at the ECM the Negative (pulse) wire going to each injector. I have a 12v test light hooked to the battery positive and the light end stabbed into the ECM plug where the pulse wire is coming out of. On the "good" driver side wire when cranking shows a bright light pulse going to injector. Then I do the same with the other injector pulse wire. It shows a very weak (dim) pulse when cranking. Looks the same at the injector as they do at the plug.

[Rally Smith]

delcowizzid:
I will give that a shot and let you know what I find.

Thanks,

[PJG1173]

Put down the test light it shouldn't be used for testing anything Efi forget you own it unless it's an Efi specific led version or a noid light for testing injector drives.unplug injectors and ecu and battery test resistance of the 12v feed from injector power relay to both injectors separately.then test resistance of the feeds from injectors to ecu

^X2 get a decent digital multi meter.

[Rally Smith]

Haven't checked resistance in wires just yet but I hooked up my laptop since I'm getting SES light now. Shows I have an Ignition Failure (code 42).
If I'm not mistaken the voltage for the injectors come off of the ignition. Will do some more checking and get back.

[joegreen]

If you live near a harbor freight you can find a coupon online for a free dvom. Thats what i do every time i break the leads on my dvom. I have two hf dvom's without leads because they always twist off at the end. They seem to work fine. Never had a bad reading. http://www.dealsoff.com/images/free_Multimeter%20exp.4-9-15.jpg

[brian617]

Harbor Freight DVOM? :mad1:

[PJG1173]

Harbor Freight DVOM? :mad1:

I had one threw it away...

[joegreen]

Oh man, everyone is hating on the hf dvom. What problems did you have?

[PJG1173]

Oh man, everyone is hating on the hf dvom. What problems did you have?

Since it was free I figured what the heck it would be a good one to keep in the truck until I figured out the accuracy was questionable. It read a little off from what my neighbors fluke read. I use his as a standard since it is on a calibration program where he works. I spent $49 at home depot and it reads the same as his fluke.

[Rally Smith]

Thanks guys, but I have a meter. (it's a piece but I have one).

[delcowizzid]

hopefully digital not an old analog swing meter LOL

[Rally Smith]

hopefully digital not an old analog swing meter LOL

Yeah, it's new-ish. I'm crossing my fingers for a Fluke for my B-Day coming up.

[Rally Smith]

Put down the test light it shouldn't be used for testing anything Efi forget you own it unless it's an Efi specific led version or a noid light for testing injector drives.unplug injectors and ecu and battery test resistance of the 12v feed from injector power relay to both injectors separately.then test resistance of the feeds from injectors to ecu

delcowizzid, I am looking at the wiring diagram for the truck and see no (power relay) going to the injectors. I see (eng-1 fuse 20A, and ecm-1 fuse 20A) but no relays.

Thanks,