Misfire On 1 And 8

Skrewball · January 24, 2008

Have a 99 5.7 out of a tahoe from the salvage yard. bought the engine/trans as a unit. the drivetrain is in a landcruiser now. i just started it the other day, when i noticed the misfire. I have heard about the poppet injecters having issues with clogging. also the intake having a common leak problem. the vacuum at idle is at 21in/hg. using my scan tool i was testing the injecters by watching the fuel pressure drop when the injecter opens. of course the pressure does not drop on the 1 and 8 injecters. the other thought would be a bent pin on the pcm when installed(custom install using painless harness)

any thoughts would be great!

thanks

vince

bobcat5544 · January 25, 2008

What was your fuel pressure drop readings for each cylinder

Indy · January 27, 2008

I've had my #1 and #8 injectors plug up on 2 occasions. I have a 5.3 though. The first time I had all 8 ultrasonically cleaned and tested at big diesel truck place. The second time I just banged the injectors upside down on a clean paper towel. You should have seen the crud that came out. It ran fine after that. I run a bottle of Techron at each oil change and have had no further problems.

You could try moving the injectors around and see if the misfire moves with them to eliminate any other possibilities.

Skrewball · January 28, 2008

to answer the first question- cyl 1 and 8 don't drop or make any noise. all of the other injectors drop and you can here them. gives two options, 1 clogged injectors, 2 no elect connection.

what i have done- i pulled the main plug from the top of the intake. using a node light i fire each injector to see if it is getting signal from the ecm. well cyl 1 and 8 are not. checked the power that is distributed among all of the injectors and it is good.

i am currently looking for the pinout of the ecm for the injectors.

what i think is the problem is the Painfull(painless) harness. i have experience the wrong location of wires on their fuse blocks for universal setups.

i am gonna do a search for the pinout, but if anyone has it could you please post it or the link.

any and all suggestions are much appreciated

Skrewball · January 28, 2008

the problem was the Painfull(painless) harness. the signal wires for 1 and 8 were not in the correct location on the ecm. Once a wiring pinout of the ecm connectors was obtained i was able to clearly see the problem. when the wires were in the correct location the misfire was gone.