GM Techs, or anyone who has replaced a Vortec Injector, help please

[sled_dog]

How do you diagnose the need for a CPI injector? I've done an injector balance test which shows the pintles as all puting out the same amount of fuel. Turn the key on, engine off, fuel pressure jumps to 65, then it quickly drops to about 59, then slowly(within a minute or 2) goes down to 51 where it sits. Doesn't start hard, or smoke on startup. But the seat of the pants dyno says its not making max power. Check Engine Light is on, there are 2 codes, P0173, and P0175. Bank 1 and Bank 2 Too Rich. Fuel Pressure Regulator was replaced a year ago to get through emissions back then(same codes). I need to figure this out because I just put a MAF on it and that was $180 of waste. I can't afford to buy a main injector right now and that seems to be what I need. Cheapest one I;ve found was a V6 one on Ebay for $200...

I'm losing it and probably missing something big because of it. I am about broke and need to sell the truck, but I can't sell it with a check engine light.

 

[ryan22re]

There is a long drawn out procedure which involves a fuel pressure gauge and a box that allows you to fire the injectors individually. Install fuel pressure gauge, fire one injector for so long. Record fuel pressure drop for that one injector. Repressurize the fuel system and repeat. One with the highest drop is bad.

Did you look at the cats? How about running some injector cleaner through it.

What do the o2 sensors do? Did you check for vacuum leaks? Saw once where the injectors go through the plastic intake, wasnt seated all the way up causing similar problems. Did you investigate the coolant temp sensor?

 

[sled_dog]

Coolant temp sensor checks out fine resitance wise, circuit tests fine.

Vacuum leak causing a rich mixture?

Used our BG injector cleaning service(add one cleaner to tank of gas, one runs through fuel rail with pump disabled until engine dies, one fogs the intake tract pre-throttle body). Will try the top engine clean idea you suggessted, had a can on hand just no gasoline and didn't feel like going through the hassle of syphoning some, just grab a can before I leave tomorrow.

Cats, after a warmup run and a beating, the one cat was 400 degrees at the start of it and 370 something at the outlet. The other was like 315 at the inlet and 350 at the outlet. Got differing reports on which end should be hotter. Temps differed pretty well from inch to inch on the cats too, either hotspots or the crappy craftsman infared temp gun.

I did an injector balance test (the fuel pressure gauge hooked up, fire one injector at a time to see how much fuel each consumes). All of the injectors consumed either 9 or 10 psi of fuel pressure when tested. Used a Tech II Scan Tool to do the test. None of the pintles tested badly through that test.

Now if I pinch off the return line with a pair of vice grips, the fuel pressure drops off dramatically(key on, engine off). Obviouslly its going somewhere. Makes me think its the main injector.

 

[ryan22re]

There are 8 individual injectors. Not just one.

Vacuum leak probably isn't it, just firing from the hip on that one. Remember that when the PCM indicates rich, its actually trying to lean things out. It sees a rich condition and leans some. O2's don't switch to lean, so it cuts more fuel. After it cuts as much fuel as possible, and doesn't see it switch to lean, it sets a rich code. Probably is why it doesn't run as good as it should.

Can't say anything about the return line pinch off test, except that it not only could be the fuel injectors, it also could be the pressure regulator and the check ball in the fuel pump.

Easy enough, you can pop the upper intake, pop the poppets out of the intake and reconnect the fuel lines. Pressurize the system again, and see where it goes. Should be able to re-use the gaskets if you are careful. I've had pretty good luck re-using them.

 

[goldwing2000]

It seems obvious but did you check the air filter?
How about those O2 sensors?
The new regulator might be bad or the vacuum control for it may be faulty in some way. If you have a leak in the vacuum line to the regulator, it could cause it to act up.

There aren't a whole lot of things that will make both banks go rich at the same time.

 

[ryan22re]

There is no vacuum line to the pressure regulator. It sits in the intake plenum, and is surrounded by manifold vacuum.

 

[goldwing2000]

K. So maybe the port got clogged or something. Never worked on a Vortec, so I'm just throwing things out there.
It could still be a faulty unit, though. I've bought bad parts before. It happens.

 

[ryan22re]

Agreed.

 

[sled_dog]

eh as it is I'm gonna pull the upper portion of the intake manifold and see whats what. I realize there are 8 poppets but technically the center fuel metering unit is called the Fuel Injector.

O2s were replaced right before the Regulator and they seem to switch fine if you watch them with a scan tool.