1995 Tahoe TBI injectors not spraying

[Daimler]

My buddy just picked up a /95 Tahoe w/ 5.7 TBI motor. The injectors are not clicking (not working) when we turn over the engine. It has been parked in a garage for the last 5 years and has 200Km on it. He first removed the injectors, cleaned them up and reinstalled them. I showed up w/ the node light and the node flashed on both injector harnesses, but the injectors still do not work. I put a 12 volt battery charger set at 2 amps directly to the injectors and they clicked and allowed some fuel to pass. Because they did not spray properly we agreed to replace the fuel pump (the complete package w/ sending unit) and the fuel filter. The injectors are still not firing, but the node light test shows the harnesses flashing. I again put 12V/2 Amp jumper lines to the injectors and the one injector sprayed perfectly and the other not quite as well. However this was a huge improvement in the spray quality. However, even though the wiring harness flashes the node light, the harness fails to fire the injectors. The flash of the node light is average, not bright, but I do not use these enough to know if they usually flash really brite. So we have injectors that work, and a harness that appears to be working but everything together does not function. I have seen posts where the ignition control module controls the firing of the injectors as well as the ignition. So maybe we need a new ignition module? Does the crankshaft sensor have anything to do with the injectors? A 12 volt test light shows voltage to both injector connectors and a voltmeter shoes 6 volts when cranking at both injector connectors. Any ideas and suggestions are appreciated. Thanks.

 

[lesterl]

The Injector harness should have 12v on one side with the key in run / crank.
The other side should pulse to Ground when cranking.
The pulsing to ground is controlled by the ECM which triggers off the Ignition Control Module and the Pickup Coil in the distributor.

So, check for 12v run/ crank on the harness, check/clean the pickup coil connections to the ICM. Does the ignition coil fire?

What is the battery voltage? How old?

 

[Daimler]

Thanks for the reply lesterl. The battery is a year old and parked for six months. It cranks the engine well and shows 12.1 volts after cranking. Both injector harnesses show 6.2 volts while cranking, 7.5 volts when not cranking but with the fuel pump running, and 10.3 volts with just the ignition on. The injector harness ground wire through a test light does flash brightly while cranking on the passenger side and the driver's side flashed brightly and then half brightly. The injector brass connectors have been prised to insure good contact at the injectors. The injectors are still not working. ( They will spray if supplied with 12 volts from the battery charger set at 2 amps.)

 

[lesterl]

Hows the battery voltage when cranking?

You have an issue between the battery to injector power connector. Power side of injector harness should mirror battery voltage, are you shure you are reading the right side of the harness? Should be constant battery on one side and no pulsing, the other side will pulse to ground so test it by grounding METER to battery +.

Battery voltage at 12.1 shows a weak or discharged battery, take battery and get it tested.

There should be a fuse for the injectors, check battery voltage at that point. Flashing of NOID light will be dim as it is a pulse and not a constant on.

Let us know what you find.

 

[Daimler]

I will have to get up to my buddie's garage to check that out. He has left for a two week shift. I will try to get up there before he gets back. I am sure we are correctly testing as you pointed out. I thought maybe the computer was dropping the voltage down to six volts - like when they use 4 to 5 volts for past throttle position sensors. I will charge the battery after doing a voltage drop while cranking test. The battery was purchased last summer from costco but it has been sitting in another unused Tahoe over the winter. I did use a test light on the fuse box and got a bright light but did not think to check the actual voltage at the fuse. I will do that too, but I will not be able to make it over there for a few days or so. Thanks for the ideas lestert. I will post as soon as I get the numbers.

 

[lesterl]

Ok, let me know if you need anymore help....

Page 13, Pink wire on injectors goes to ECM-1 Fuse 20A in underhood fuse relay center. There is a splice that also feeds the same feed to the ECM behind the glove box pin E15 also a pink wire..... Good luck.

 

[Daimler]

Hey Lesterl, it is now running fine.Once I read the wiring diagram you provided I could see the 12 volt circuit and understood there had to be a connection issue dropping the voltage to six volts. My buddy got back from up north and came over for supper and we went through the wiring diagram (Page 13) as well as our posts. I had to work the next day and he tackled the job. Although the fuse for this circuit (20 amp ) lit up my test light during the original troubleshooting, he found that one of the two fuses showed an open circuit when he ohm tested it. Looked O.K. he said - yet did not pass the continuity test. He replaced the fuse and she fired right up. He said someone else had warned him in the past NOT to trust these fuses. They can look O.K. but actually can be open! Kinda blows my mind - no pun intended? Feel a little stupid on this one, but live and learn I guess. Lesterl, I gotta say thank-you big time for your help and the great wiring diagrams. Guys like you make a site like this rock!

 

[lesterl]

Yea, glad you gotter going!!!!