LarryD

What are the symptoms of mis-wired fuel injectors?? Trying to help a friend who replaced head gaskets and now on starting it sounds like it is backfiring through the intake on one cylinder (popping sound through the air cleaner bucket) and barely runs. Except for the head gasket leak, it was running pretty much fine before disassembly.. Nothing was changed to disturb timing and the plug wiring has been checked several times. This is an 89 2.8L in a Z24 Cavalier so no dizzy...

327_TPI_77_Maro

iTrader: (8)

Backfiring through the intake on one cylinder could be a bad intake valve. Is that motor SEFI or batch fire?

Six_Shooter

iTrader: (2)

It's batch fire and you could completly "screw up" the order of the injectors, and have absolutly ZERO effect on how the car runs, since all 6 injectors fire at the same time in that car. Also you'd ehave two cylinders out, not just one.

daves12secV6

iTrader: (3)

possible over tightened rocker arm on one of the intake valves?

Al Hasse

I had set of injectors cleaned and serviced and one went bad as soon as I put it back in. Wasn't firing at all and gave similar symptoms with an occasional backfire. Mechanic took a heavy duty test light and grounded one spark plug wire at a time (poking through the boot on the dizzy), found the bad one when the engine RPM did not change when grounded.

327_TPI_77_Maro

iTrader: (8)

Even if an injector is not firing it shouldn't backfire through the intake, that means an intake valve is not closing. It sounds like either a bad intake valve or an overtightened rocker holding it open.

Six_Shooter

iTrader: (2)

You can't overtighten a rocker arm on a genII 660.

Though I do have to ask, because somehow people do this:
Are all the pushrods in teh right spots? The genII uses two different length pushrods for theintake and exhaust valves.

LarryD

Well, I wasn't around when he and a friend did the reassembly. I asked about the rocker being too tight and they said that these are non-adjusting type and you just "snap" them down into place (never seen this type so don't know how they work myself). I wasn't aware that this engine had different size push rods (my 92 Camaro 3.1L has all the same length which is my only comparison experience) so will ask about that. I looked at the wiring diagram for the injectors and see that it is designed to alternately fire each bank of injectors (1, 3, 5 in parallel and then 2, 4, 6 in parallel). So, wouldn't a backfire through the intake be possible if one was switched, like 5 and 6 reversed or 3 and 4 etc., yet all the rest are correct?

327_TPI_77_Maro

iTrader: (8)

If it's batch fire it shouldn't matter. Even though the driver fires them alternately, ultimately the only thing that matters is the pulse width, which is the same for all injectors. It's probably the pushrod issue.

2_point8_boy

Excellent thought. I've seen a lot of people put them together wrong because they didn't pay attention to how they came out, then they tow it to my shop where I have to take everything apart again to get to them. It's not as bas as doing it on our cars, but there's a lot of stuff in the way on the back side.

LarryD

My initial thought when I heard it was that the timing was off which would also sound like a valve open when it shouldn't be, hence, the wrong pushrod on the wrong valve with them being different lengths then... It almost sounds like only one cylinder is backfiring so maybe there is just one that has the pushrods backwards... Looks like though that pushrods is the most likely scenario... Not sure how many beers and/or shots were consumed at the point at which the pushrods and injectors went back in, hmmmmmm.... It looks like the upper air plenum would have to come off but can they be changed around on that engine without pulling the intake manifold?? I'll probably help him pull it down to the pushrods tonight... Given today's gas price its worth the effort right away since he is stuck with his 70 Ford pickup at 7mpg until he gets this running.

Six_Shooter

iTrader: (2)

Forget what you think you learned from that wiring diagram, because it's wrong.

Yes each bank has it's own dedicated injector wire, but going farther back, inside the ECM, you will see the injector outputs are bridged, internally, making all 6 injectors fire at the same time. I've had a few of those ECMs apart.

I am going to attempt to modify an ECM and code to make them alternate like it looks they do, so that I can run a larger injector easier.

LarryD

I've not had an ECM apart to see how it is connected internally. While I was at work yesterday, he pulled the upper intake off and checked the injector wiring. They seem to be wired fine. He was a bit tired of working on it last night so didn't want to dig into the pushrods until this weekend. He understood when I told him about the different size pushrods and said that he asked the guy who helped him if they needed to keep them organized to put back in the same way. The guy told him no, didn't need to do that... Oh well......................

daves12secV6

iTrader: (3)

ouch,yeah pushrods should always go back were they came from,same with rockers and lifters,just like u wouldnt pull the pistons out of a short block and reinstall them in diff cyls.

LarryD

Well, the results are in.... Looks like they got somewhat lucky and only one intake and exhaust pushrod were reversed.. Unfortunately, I just finished helping him pull one of the heads for a bent valve.. Intake on #6 had a nice "S" shaped exhaust pushrod and the valve hit the top of the piston... Looks like the piston is ok but the valve needs to be replaced....