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1988 Vette, Code 44 Lean Exhaust problem


May 30, 2012
Moriac, Victoria, Australia
Hi Guys,

I have a code 44 (Lean Exhaust) issue on my 1988 Vette.

The car is completely stock with 47k miles on the odometer.

Approx 2 years ago I installed new intake manifolds gaskets due to a coolant leak on the LH side, all intake/plenum runners, throttle body etc gaskets were replaced at the same time.
The original injectors were cleaned, flow tested and refitted.
A new 02 sensor was fitted along with a new IAC valve.
BTW the code 44 and running symptoms existed before I did the gaskets, 02 sensor and IAC valve replacement.

Running symptoms are:

Generally slightly rough idle, not too bad, but not as smooth as it should be and RPM sometimes varies marginally.
Occasionally when idling (and fully warmed up) the idle speed will drop and surge momentarily for a few seconds and then corrects itself and returns to reasonably consistent 700 rpm idle.
Also when restarting the car ( after the car has been driven and fully warmed up) the idle speed is high, usually around 900-1000 rpm, then after 10-15 seconds it will slowly drop back to normal.
Last time when I drove the car (approx 6 months ago) I felt the engine miss/stumble momentarily and then it started running ok again, it felt like 1 cylinder was not firing.
Then weeks later when I started the car to move it out of the garage, it was running very rough, had a definite miss and sounded like it was only running on 6 or 7 cylinders.
Today when I started it for the first time in months, it ran ok, not rough or missing.

I’m suspecting the injectors, being that they’re originals and are known for causing problems.

Things I’ve done/checked today.

Fuel pressure:
46 psi on the 2 second prime, and held the prime pressure without dropping.
Consistent 42 psi whilst running, regulator seemed to vary pressure ok as the rpm’s increased/decreased.
Holds a steady 40-42 psi pressure for 10-15 minutes after engine has stopped.

I did a injector balance check test (comparing pressure drop of each injector) as per the procedure in the FSM.
The test basically states that “any injector that has a pressure difference of 10kPa , either more or less than the average of the other injectors is considered to be defective”

I performed the test 2 times and got the following pressure drop numbers for injectors on LH bank (1,3,5,7) and RH bank (2,4,6,8)



Ok so it would seem injector 6 is delivering too much fuel (rich), but the others aren’t exactly consistent either (152-166kPa) if you know what I mean.
On the LH bank we’ve got 3 injectors matched at 152kPa drop and 1 with a larger 166kPa drop.
Then on the RH bank we’ve got 3 injectors with 166kPa drop and 1 (number 6) with a 180kPa drop.

I’m not exactly sure how I should be interpreting these figures.
Should I be adding all 8 values together and dividing by 8 to get the “average” number and then comparing against that?
Or should I just consider that the difference between 152 and 166 is greater than 10kPa and therefore condemn all of those 7 injectors (along with number 6)?
Is it simply the general inconsistency of the injectors that’s likely to be causing the issues?

Also there’s only one 02 sensor, on the left hand exhaust pipe, so I would assume the ECM doesn’t know/care what the RH side is doing?
Taking the location of the 02 into consideration, I’m chasing a lean condition, but I’ve got 3 injectors on the LH bank that seems to be matched on flow (152kPa) and 1 that’s over delivering (166kPa), so wouldn’t this produce a rich exhaust code?
The readings from the 02 sensor also seemed to have a wide fluctuation as well, it was constantly changing from as low as 90mV to as high as 740mV, I don’t know if this constant quick fluctuation is normal or not?
According to the FSM, voltage below 350mV is lean and voltage above 550mV is rich, my readings would seem to indicate that the engine is constantly fluctuating from rich to lean?

The Block Learn (BLM) was 120 at idle, this means it’s running lean correct?
Increasing the RPM and holding, only increased the BLM to 122 after a few minutes.
Also the Fuel Integrator value was varying between 125-132, so it’s pretty close to 128 but is adding some fuel to try and correct a lean condition correct?

I also checked the resistance on the injectors, both cold and hot.
Cold was 15.9 ohms for all 8 injectors, and hot was 17.3 for all injectors.

I’m not sure what I should do/check next?
I don’t just want to throw parts at it, I want to actually diagnose what part(s) are defective and replace as required.
What do you guys think, am I over thinking this and should I just replace the injectors, or could it be something else?

Thanks, Ken D
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