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)

1=152kPa
3=152kPa
5=166kPa
7=152kPa

2=166kPa
4=166kPa
6=180kPa
8=166kPa

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 each injector 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 something else?

Thanks,
Ken D

 

120 is rich, but not a bad number. Below 128, rich, above it, lean. Still, those BLM numbers are great. I would start simple and do smoke test to reveal if there's any vacuum leaks.

 

Thanks 1993C4LT1, I knew I'd get the BLM thing backwards!....pretty sure it's stated in the FSM somewhere, just couldn't find it at the time.

Makes sense if it's running slightly rich, there's 1 injector on the LHS that's appears to be over delivering.
I was considering doing a smoke check next, been looking on youtube for the best DIY homemade smoke test machine.

Ken D

 

I had an inspection shop do a smoke test on my 93 last year. It was like 20 bucks. Worth it to me, because I don't smoke. Nor did I want to make some weird contraption

Oh, and the o2 sensor going rich to lean rapidly is normal. Say if it was stuck in one position, or very to slow react, it would indicate a bad o2 sensor. But that's not the problem here.

 

Dumb question. Since you have a code 44, did you follow the diagnostic for it?

 

Yeah I don't smoke either (never have), I'm pretty confident I can make a pretty good smoke machine using equipment/materials I've got at work.
Thanks for the 02 info, good to know.

 

No problem

And if you look at o2 data when the car is in open loop(cold engine, or even with a warm engine it will be in open loop for a while if you just started it), the o2 may look dead. Normal because o2 comes into account when in closed loop only.

 

Yes for the most part I did.

From the FSM:

1.Using the "Scan", observe the block learn values at different rpm and air flow conditions. The "Scan", also displays the block cells, so the block learn values can be checked in each of the cells to determine when the code 44 may have been set. If the conditions for code 44 exist, the block learn values will be around 150.

I'm using a Tech 1A scan tool (which I'm pretty new to and still learning my way around it) As far as I can figure, the Tech1 doesn't display the block cells?, only a overall BLM figure and Integrator value.
The BLM displayed by the Tech1 wasn't anywhere near 150 so I disregarded this check.

2. 02 Sensor Wire: Sensor wire pigtail may be mispositioned and contacting the exhaust manifold.

I checked the sensor wire and it was still clipped into the factory wire retainer and nowhere near the exhaust.

3. Check for intermittent ground in wire between connector and sensor.

I wasn't exactly sure how I should check for this, so I skipped this check.
I'm assuming you check for continuity from the connector ground pin back to ground (i.e. the block/manifold etc?

4. MAF Sensor: A mass air flow sensor output that causes the ECM to sense a lower than normal air flow will cause the system to go lean. Disconnect the MAF sensor and, if the lean condition is gone, then replace the MAF sensor.

I didn't do this because I figured if there was a problem with the MAF sensor I'd see a code for it?...and the MAF/airflow numbers being displayed via the Tech1 were in line with what the FSM recommended.

5. Lean Injectors: Perform injector balance test CHART C-2A

I did the balance test, figures/results are as above.

6. Fuel Contamination: Water, even in small amounts, near the in-tank fuel pump inlet can be delivered to the injectors. The water causes a lean exhaust and can set Code 44.

I have fresh 98 octane fuel in the car, and I never put that Ethanol crap in it, so I ruled out the possibility of water in the fuel.

7. Fuel Pressure: System will go lean if pressure is too low. It may be necessary to monitor fuel pressure while driving the car at various road speeds and/or loads to confirm.

I monitored/checked the fuel pressures as above, although I didn't do any monitoring/checks whilst driving. I may end up doing this if I can't get this lean condition sorted.

[I]8. Exhaust Leaks: If there is an exhaust leak, the engine can cause outside air to be pulled into the exhaust and past the sensor. Vacuum or crankcase leaks can cause a lean condition.

I checked the LH exhaust/flange etc for tightness and it seemed to be ok.
The vacuum/crankcase leak side of things, I haven't done, hence the need to smoke test.

9. AIR System: Be sure air is not being directed to the exhaust port while in closed loop. If the block learn value goes down, while squeezing the air hose to the left side exhaust ports , refer to CHART C-6.

I tried this test (whilst in closed loop) and it made no difference to the block learn values. So I took this as meaning the AIR system is performing ok.

 

It definitely sets a code 44, I've had a problem with this code reoccurring quite a few times. I've confirmed it's a code 44 by grounding the OBD terminals A+B and via the scanner.
I know you would think it'd be a code 45 based on the BLM's indicating it's running rich, but it must be doing something different (running lean) whilst driving.
I'm going hunting for vacuum leaks next and I'll take it for a drive with the scanner and see if that shows up what the BLM is doing.

 

As stated earlier the BLM's you show and discuss at idle and at a slightly higher throttle position are slightly on the rich side. If you are getting a code for lean exhaust you may be getting this during some part of the drive cycle and you should scan that to see when it shows up. As far as the 02's bouncing over and under 450mv that is normal and is what it should be doing.

Overall what you show does not appear to be an issue. Since 4 out of 8 injectors show a pressure drop of 166kpa I would consider that to be the standard. (I am guessing there but I really do not think that is the problem)

 

I agree with bjan, but i've never tested the injectors that way. And yeah, you did follow the diagnostic. Good on you for that. I would do the smoke test and go from there. See when the BLM goes lean, and look at fuel pressure at the same time, if you can.

 

check your exhaust, from the exhaust manifold gasket to the 02 sensor. i've seen situations where a comprimised exhaust seal draws in unmetered air, which mixes and makes the gas flowing past the 02 sensor leaner.

check that.

also, you can buy a $1 cheap cigar, tape off the big oval throttle body intake, and then blow smoke (i didn't inhale because i don't smoke either!) into the brake booster vacuum hose. pull it off the booster. blow and blow and blow and blow. have a friend or wife look for smoke with a flash light. i found mine this way. i had to put a lot of smoke into the pipe to see it. i needs some pressure behind it if it is a small leak like mine was. (the rubber hose from the pcv system on the driver side, from metal pipe along the valve cover up to the intake manifold nipple was cracked and sucking in air.)