Hello all; I've got a v6 MPFI 2.8, but I use a cold start injector, and one injector per cylinder, just like you MAF-equipped v8 TPI guys do... and I have a question.

I've got a leaking injector- I've known this for over a year! I verified this with a fuel pressure gauge, and by following the procedure in the GM service manual for my '86 Firebird. (At first I thought the damn pump died; I've replaced that SOB twice already.. wasn't looking forward to doing it a third time.)

I was wondering if the cold start injector can leak? I don't know which injector's leaking; and I don't want to pull the rail out to check. Every time I've pulled a rail, pintle caps snap, o-rings tear, etc- and why install old injectors again? If it -is- possible for the cold start injector to leak, is there any way to find this out without pulling the CSI? Or am I basically screwed, and have to pull all the injectors out at once? That sucks; the car's my daily driver.

 

Sure it can leak, it is an on/off injector, just like the main injectors. To eliminate it as the cause of your problem without removing it you could take the fuel tube for it off the fuel rail and put a plug in the rail. Your cranking times will be longer but you can then do the injector balance check without a possibly leaking CSI giving you skewed readings and pinpoint which injector is leaking.

 

Bitchin' idea! Thanks! Then I'd only have to pull off the plenum. Didn't think about plugging that up. Ugh; what would I use? A metric pipe plug? Anyone know the threading? I assume it's the same size as for TPI.

Oh, and how could I do a balance test when pressure drops to zero almost instantly? I have a balance tester, but figured it was pointless if pressure drops so damned fast.

Think I would see a wet spark plug, if I pressurized the system a few times when the engine was cold?

 

If pressure is drops off immediatly you need to try crimping off the fuel lines to determine why. First try crimping off the supply line as soon as pressure raises in the system. If that holds try crimping off the return line and turn the key on. If it doesn't hold when crimping the supply line then you have either a leaking injector(s) or regulator, if it doesn't hold when crimping off the return line you have a leaking pump checkvalve or coupler hose in the tank.

 

Yep, like I said, I already did that test; it came down to a leaking injector. Went further by testing the regulator (keep return line crimped, crimp supply line upon pressure), and that leads to an injector.

 

Ok, well this was kinda vauge;
"I verified this with a fuel pressure gauge, and by following the procedure in the GM service manual for my '86 Firebird."

Never read the service manuals so it meant nothing to me.

Anyway, disconnect the CSI and try the crimp test again, if it drops that fast you have an injector stuck wide open. Prime the system a few times and start removing plugs and smell them, one should smell very strongly of gas (maybe more than one too).

 

Oh, okay, no problem. Yeah, the GM service manual tells you how to diagnose everything, just as a pro mechanic would. That's why I said that my system (v6 MPFI) is the same as the v8 TPI system; if someone didn't know about all the engines, they'd assume I had some totally different injection system.

Stuck wide open, eh? Could I verify that with a multimeter?

I pulled the plugs yesterday (without disconnecting the CSI), couldn't find one wet with fuel. I primed the pump twice before yanking each plug, too.

I did find out that my MSD 6AL and MSD Blaster SS gave my AC plugs a hell of a beating, though. The ground electrode of each plug was basically dug out like a half-circle, centered above the center electrode. Gap widened up from stock 0.045" to an 0.060! I set the gap back to 0.045, but nope, same driveability problem. Hopefully next weekend I'll be able to spend more time on the car.

Anyone else got any experience with the CSI? How do you TPI guys do this block-off I've read about? Do I actually need to change my PROM for this? Seems like the CSI circuitry is comletely independant of the ECM...

 

Don't count on it but it is worth a try. If it is just stuck then it is a mechanical failure of the injector and ohming it won't help.

How is your CSI plumbed into the fuel system? On a TPI it has a tube that runs around to the backside of the driver side fuel rail and screws into it. If yours is something like this, you could unscrew the line and plug the rail with the proper size plug and see if that helps the driveability. Be warned, you will have a much longer crank time with the CSI disabled.
As a quick test to see if it is being commanded open all the time, remove the connector to it and try starting and driving it. It is possible that the thermo-time switch is stuck on all the time and is making the CSI stay open.

 

Yep, same as the v8's... the cold start line comes from the top of the fuel rail, and goes around to the back of the manifold, where the cold start injector sits.

Good idea about the cold start switch "thinking" it's cold out, and being stuck closed. I'll be able to run more diagnostics on it this weekend.

What about killing the sucker permanently? Would I just have trouble starting in the winter? I'm not about to convert over to speed density just to get rid of the cold start injector! And prom burning is probably a year or two away; got too many plans for the car this summer to spend the time (and money) burning my own prom.

It's been warm enough lately (well, except for today!) in NJ that the CSI shouldn't be coming on anyway.

 

I killed it on my v8 by changing to a later chip which it was deleted in in favor of cold start enrichment. That meant changing to an 88 chip from 87 for me. You'd have to research to see if the v6 is the same.

May as well check the cold start switch and see if it's accurate, that could cause it to dump fuel in. It wouldn't make it leak with the car off, though. On my car I can pull the csi out in like 2 minutes.. it's just a bolt and it swings out. V6 is different?

 

The CSI is activated any time the coolant temp is below 95* F during start. As the weather gets colder your crank times will increase.