experienced help needed ASAP 3.1 prob

[gutlasscutlass]

I have a 1995 chevy lumia with a 3.1. I had a missfire problem and determined that it was the injector. Cause i had compression and spark going to that cylinder and because of the 3.1's upper intake plenum you cant get the the injector harness to check for pulse. So anyway I changed the injector on the #6 cylinder. Started it and it ran smooth but was racing at 1200 at idle. Checked for vacum leaks found none. Found that when I raced the motor it back fire out of the egr valve. So i changed the egr valve gasket. Now when i started it again and whatever spray i used to clean that passage caused a back fire when i started it. Since then that car is running really bad. The car races at idle has a miss and sometimes just dosent start at all. Plus if you play with the map sensor it runs better or worse. I have try'd 2 map sensors to the same result, and i have swaped out ignition modules. My snap-on MT2500 also now does not communicate with the computer. Any ideas?????

[no1kicker]

No idea, but did you reset the ecm?

[dbtk2]

After it backfired did you check the plugs? That could've broken a plug or something, causing it to miss.

 

Shawn

[gutlasscutlass]

I cleared the codes with my scan tool. How do you reset the ecm??

[White93z34]

just disconnect the battery for about a minute.

[Canada]

I cleared the codes with my scan tool. How do you reset the ecm??

 

I thought you said you couldn't communicate with the PCM?????

[Jcrow]

The high rpm at idle tell me its a vacuum leak, I know you said there wasn't any but how about the IAC idle air control. They are cheap, mine fell apart. Also check the vac line to the transmission.

PS All fuel injectors pulse at the same time - I checked with an oscilliscope

[Robby1870]

He's got a 3100 SFI, so no, the injectors dont pulse at the same time. On a 3.1L MPFI, they do.

[Jcrow]

oops

[Tim]

He's got a 3100 SFI, so no, the injectors dont pulse at the same time. On a 3.1L MPFI, they do.

 

Is that to say that the 3.1 dumps fuel in each cylinder regardless of what point in the cycle that cylinder is in?

Tim

[Jcrow]

yes, SFI stands for sequential fuel injection. So the injectors fire in sequence. Correct me if im wrong but I think SFI reverts back to batch fire over a certain RPM 3000?

Yeah and the 3.1 MPFI is batch fire - where all injectors fire in a batch

[Slade901]

Re-check your vacuum hoses. On mine, the vehicle backfired when I started it and when I started it again the vehicle's idle was bad and barely move. I drove the vehicle quickly back home before I get stranded at the street. I was checking for error code and other sensors and not realizing that the problem was just the vacuum hose on top of the throttle body was pulled out a little bit due to that back fire. Reconnected the vacuum hose again and started the engine, the engine runs better after that. Since then, I have rigged something so that vacuum hose will not pull out if I even got another back fire again.