Leaky Injectors Diagnosis
 

I think I know the answer to this however, I thought I would enlist advice.

I have a hard starting problem. It seemed that within a day I developed a hard starting problem. It usually happens after the vehicle sits for about an hour.

The key to the diagnosis is that it takes a few seconds to start vs the less than a second it use to take. However if you open the throttle up about 1/2 way it starts up. Sometimes there is a bit of a puff out the exhuast.

It really seems like a carb that flooded.

I did a test with the fuel pressure. It goes up to 55-58 (hard to see it). Then it drops a bit, and it should hold steady for a while, but it does not. It leaks down in less than 20 minutes. So I assume there is a bad injector or two (or more).

Originally I thought it was the cold start system, but that checked out.

All my plugs look fine. Diacom shows nothing out of the normal.

My injectors are a set of 19lb running at 55lbs which gives me a block learn value around 138. The injectors are the pintel style bosch brand. I had them cleaned too.

So the question of the day. Does the higher than normal fuel pressure cause the injector to wear out or leak? Or do I just have old injectors?

Sorry to be so wordie ... bad habit.

Mark.
'85 Jimmy 2WD, 5.7TPI, AFPR, 52MM, airfoil, ported upper/lower, ZZ3 cam, Edelbrock 6089 heads, 700R4, 3.73 posi, stock 87 5.7L prom (and it works!)


[This message has been edited by Mark_ZZ3 (edited September 13, 2000).]

Yeah, it sounds like your injectors might be leaking. or your fuel pump check valve is going bad. Or a leaky AFPR, which is usually not the case.

Injectors are most likely the problem. I would nt think you wore your injectors out faster, because the only time the duty cycle is loading on the injector is when your flooring it, normal driving wouldnt make it go out any faster IMHO.
Some how if you could pressurize the system and block the return line to see if it holds.. If so, you got a bad regulator.. pressureize the system and block off the inlet side..if it holds, you have a bad fuel pump. If it drops with both those 2 steps, you go a leaky injector.

The only problem is to find a place on the fuel lines to block it off. Most cars I use a simple vise grip on a rubber line, but if i remember correctly, the 3rd gens have al metal lines... which would suck trying to block off

[This message has been edited by Kevin G (edited September 13, 2000).]

Actually, there is a flexible rubber section in each of the fuel lines (return & supply) that you can pinch off. On my GTA 350tpi the metal fuel lines come up on the drivers fender, convert to rubber for a foot or two, then back to metal to go into the fuel rail. You can block the flow with vice grips to test (be careful not to puncture the rubber).

I had the same problem and my mechanic did this test and confirmed that with both lines blocked the fuel pressure still dropped 20psi in about 5 minutes. I tested the injectors by (and this is the Readers Digest version):
-pulling the runners & plenum
-disconnecting the electrical from the injectors
-unbolting the fuel rail
-popping the rail with injectors up out of the manifold.

At this point all the lines are still connected. Support the rail so the injectors are free (hanging from the rail) and pressurize the system (turn the key on - DO NOT START). Leave it pressurize for a minute or so, then turn the key off. If your injector(s) are leaking gas will leak out the ends of the injector. Putting some paper under each injector works very well to detect the leak.

I did this and found I had 7 leaky injectors!!! I had them all sonic cleaned and flow matched and it starts like a hot damn now.

Good luck. If you want more info feel free to email me.

Eric

------------------
87 GTA 350 TPI, 700R4,
K & N, Accel cap/rotor/wires, SLP airfoil, ported plenum

Re: Leaky Injectors Diagnosis
 

You can also just run the car for a minute or so, then pull the plugs. If you have any wet cylinders you have leaky injectors

Re: Leaky Injectors Diagnosis
 

unless the intake valve for a cylinder is closed

Re: Leaky Injectors Diagnosis
 

I've found that something like this and a fuel pressure gauge to be a real time saver when looking for a leaking injector.

http://i3.photobucket.com/albums/y94...psb11e37c7.jpg