After installing an edelbrock intake, runners, AFPR, and new ignition on a friends 87 IROC, the car idles very rough when in gear. After testing the FP, it hits 47 at idle, raises slightly when you hit the gas (but drops right back down), the strange part is when you shut the car off. The FP DROPS to around 6-8 psi in about 4 seconds. It would seem like an injector is sticking/bad, any other ideas? The car holds FP when running and driving, but it drops like a rock when shut off.....

Timing is set at 10*, all new plugs, wires, MSD box. New AFPR set to 47.

Any suggestions? How can you test for an injector stuck open?

Thanks,

 

Certainly sounds like a leaky injector


any black smoke on startups? or does it crank a few extra times?

 

It does both, it seems to take longer to crank and start, and there is black smoke on start-up, acceleration, and coasting. While coasting we are also getting some exhaust popping as well. It sure does point to an injector.....

Is there any way to test for a stuck injector? The only thing I can think of is to remove the upper intake and fuel rail, then pressurize the system and see if any of the injectors are leaking. Is there another way?

Thanks for the input,

 

Maybe pull some spark plugs and see which one is blackest

 

put a small washer under the 4 bolts between the intake and the fuel rails. This problems is very common for edelbrock intakes. Tightening it down all the way is grounding out the injectors and always keepnig them opened. FP shoudl be around 40 at idle with vac line connected and about 46 when disconnected.

 

Question about the grounding of the injectors: As I understand the injector pulses, the 12V is pulsed to the injector to open it, or is it the other way around where there is always 12V and the ground is signaled? If the 12V is pulsed, how would the injector be grounding out when the only time it could ground is when the 12V pulse is sent? Just trying to make sense of it, but it sounds like that is our problem, one or more are now sticking open, cause it was fine before doing the swap....

Thanks for the suggestions!

 

I just checked out the wiring diagram for an 89, and your theory makes perfect sense, the injectors are getting 12V with ignition on, and the ECM is grounding to fire the injectors, which if the injector is seating incorrectly it would ground it out and cause it to fire ALL the time! Is there any way to test for this while everything is on the car? Also, with the ignition OFF, shouldn't the injector close? I ask this because we are losing ALL our pressure in about 4 seconds when we turn the ignition OFF, or would the injector stay open?

Thanks again!

 

They would stay opened. Loosen up the 4 bolts on the rail a little and see what happens. For this other person he was on this board for 3 months trying to figure out this problem. And this was it.

 

We'll be trying this later today (Sat.). Since we are pulling the upper intake off, the fuel rail will be easy to get too and try this out on......

Can you tell me why they injector would stay open if it's not getting the 12V to activate? Just curious as to how it works now.

Thanks again, and I'll post the results tomorrow......

 

Well, it's fixed! The injector was grounding out on the intake like mkos1980 said! When we loosened the fuel rail the system held pressure right at 47. Needless to say, we put the washers under the fuel rail and tightened everything back down, now it runs like a champ, a bit lean on idle as expected, but tons better than before! Kudos to mkos1980!:hail:

Thanks again everyone for the input!