Tampa 928s

That's what I thought, I am sending the Maf back to have it check again. I believe it must be the Maf, unless someone tells me different. I'll be glad when I can actually drive this car for more then 2-Days at a time.

Tim Murphy

Page's 24-204, 205, 206 is the procedure for adjusting idle speed (and does mention adjusting the CO on the air volume sensor).

Page 24-207 is the procedure for "Correcting CO Adjustment On Air Volume Sensor" and doesn't say anything about disconnecting the O2 sensor.

Tampa 928s

This is what I used to check out the CO adj. Am I missing something or do I not really have a problem. I was told to check it with Ox sensor disconnected than told it needs to be connected. Keven told me to check it with it off and this is the readings I came up with. Once the Ox Sensor was reconnected it was more in line with the specs. I'm so confused

Tim Murphy

Yep, pretty much says the same thing in the WSM that I have but it is listed in the "Adjusting Idle" section.

I agree with John that the best way would be to adjust it without the 02 sensor because that will put you more in the middle of the range so you have less correction from the 02 loop.

If you can't get to 14.7 AFR without the 02 loop then I would suspect the MAF is not in spec (?????)

Maybe the TempII sensor is over-riding somehow and causing the bias. Totally guessing here.

I have an 86.5 car here and it definitely targets 14.7 at idle even with larger injectors and stock fuel pressure.

Z

Have you disconnected the vacuum lines from the fuel pressure regulator, fuel pressure dampers, and FMU to check for the presence of fuel? If an internal diaphram in any of those is damaged it will allow fuel into the enginre through the vacuum lines that attach to the connection ports on those devices.

You may want to do a free air calibration of your LM-1. Steady part throttle cruising in your logs shows the air/fuel ratio swinging back and forth, like it should in closed loop operation. Normally the LH closed loop adjusting swings the air/fuel ratio back and forth trying to maintain a 14.7:1 average based on the stock O2 sensor feedback, but your LM-1 log shows it swinging back and forth with a richer than 14.7:1 average. Your LM-1 may be displaying an incorrect, richer than it actually is air/fuel ratio.

If the LM-1 logging is accurate, the stock O2 sensor signal voltage going to the LH may be higher than it should be for the actual air/fuel ratio for some reason. Are you sure you don't have any leaks in the exhaust system allowing fresh air into the exhaust system ahead of the stock O2 sensor? (This would have to be a leak allowing fresh air in at a location that the stock O2 sensor would pick it up but the wide band O2 sensor wouldn't.)

The signal from the MAF sensor is tapped into, goes to the voltage divider that you made, and then the voltage divider connects to the LMA-3. You might want to try disconnecting the wire that taps into the MAF signal from the voltage divider, to make sure that the LMA-3 or the voltage divider aren't affecting the MAF signal.

John,
is the CO adjusting pot functional on the US specification '86 that came equipped with cats and an O2 sensor? I know that it's not functional on '87+ US cars, but that on ROW '87+ cars it is.

John Speake

Hi Z,
Yes, the pot on the MAF is still in circuit on 85/86 US 32v cars. I suspect there is a simpler O2 loop algorthm in the LH2.2.

You are correct concerning the >87 cars (LH2.3)

Tampa 928s

I did check for fuel in the FPR Etc, once I adjusted the Maf several turns to lean my A/F gauge then started to bounce back and forth. My question was with the Ox sensor disconnected I cannot get it to beyond 11.5 A/F. With the Ox sensor connected I can adjust it to a normal range. After this adjustment my A/F gauge began to act normal. My thought was that the Maf was not adjusted correctly for my S/c set-up.
From what I conclude to set-up C.O. correctly Ox sensor is disconnected the Lh defaults to mid range I then should adjust for a 14.7 A/F ratio.
The problem is only with the Ox sensor connected can I adjusted this A/F correctly.
Does this indicate a Maf problem which the Ox sensor is compensating or a normal set-up.
I can do another free air calibration but did it 3-weeks and 75 miles ago. My exhaust is tight and do not see an issue with that although it could be in question with the C.O. tube connection off of the manifold.
The Maf did have a problem with the driver circuit along with it being out of calibration. I was told a 40 Mv range is normal my was at 140 Mv. This would explain the problem with it running inconsistently but not the issue of stalling after it was reinstalled.
So should I send it back, it's in the box now or is it just an adjustment issue and one of you is wrong.
According to what I am reading not being able to adjust the A/F ration with the Ox sensor disconnected indicates a problem.




Have you disconnected the vacuum lines from the fuel pressure regulator, fuel pressure dampers, and FMU to check for the presence of fuel? If an internal diaphragm in any of those is damaged it will allow fuel into the engine through the vacuum lines that attach to the connection ports on those devices.

You may want to do a free air calibration of your LM-1. Steady part throttle cruising in your logs shows the air/fuel ratio swinging back and forth, like it should in closed loop operation. Normally the LH closed loop adjusting swings the air/fuel ratio back and forth trying to maintain a 14.7:1 average based on the stock O2 sensor feedback, but your LM-1 log shows it swinging back and forth with a richer than 14.7:1 average. Your LM-1 may be displaying an incorrect, richer than it actually is air/fuel ratio.

If the LM-1 logging is accurate, the stock O2 sensor signal voltage going to the LH may be higher than it should be for the actual air/fuel ratio for some reason. Are you sure you don't have any leaks in the exhaust system allowing fresh air into the exhaust system ahead of the stock O2 sensor? (This would have to be a leak allowing fresh air in at a location that the stock O2 sensor would pick it up but the wide band O2 sensor wouldn't.)

The signal from the MAF sensor is tapped into, goes to the voltage divider that you made, and then the voltage divider connects to the LMA-3. You might want to try disconnecting the wire that taps into the MAF signal from the voltage divider, to make sure that the LMA-3 or the voltage divider aren't affecting the MAF signal.

John,
is the CO adjusting pot functional on the US specification '86 that came equipped with cats and an O2 sensor? I know that it's not functional on '87+ US cars, but that on ROW '87+ cars it is.

John Speake

Hi Mark
You are correct, you should be able to set 14:1 at idle with the loop disconnected. The loop is trying to pull the A/F back to stoich, but that's not like it should be, with the mid range value stuck at 11.1.

I would double check your WB free air calibration ,although the fact that the A/F goes to 14 when the loop is closed indicates it is pretty close.

It looks as though you may have to send the MAF back.....

Tim Murphy

If this tube was cracked or broken off it would have a big influence on the 02 sensor getting a false reading since they connect to the exhaust before the 02 sensor. The engine would think it was lean and try to richen up the mixture. You would also see a lean reading on the narrow band gauge connected to the 02 sensor. Also, make sure the shield on the shielded wire on the computer side of the 02 plug is not touching the signal wire. This will also mess with the signal.

I provided 2 small ball bearings to plug these the C0 test tubes at the exhaust manifold. Any chance you still have them? Most of these tubes are rusted through and should be removed as PM.

Tampa 928s

Tim,

I did notice a crimp near the tube where it connects to the Manifold, you need to send me a couple it did not come with my kit. Would I not hear a noise coming from it if it was leaking? Remember how good it ran ????? I'm still betting on the Maf!

Kevin Michael

Tampa, have you tried removing the belt from the SC and logging the car NA? I doubt it's the SC but it would be good troubleshooting.

Tampa 928s

No, thats the last thing I will try!

Shane

No You wouldn't. I had one that was broken in two that I'd didn't notice until I removed the bolt that was holding it to the intake plenum, then I noticed...

Tampa 928s

I checked mine out and they both look in pretty good shape. I think the kink was caused by P.O. trying to take it off, looks like it is twisted a bit.
As a side note; Maf was picked up today no charge, I am real curious if it is indeed bad. It makes sense that with the Ox sensor disconnected and the Lh mapping at a middle state it should adjust enough for a 14.7 A/F ratio.
Once the Ox sensor is back into the mix it reads a lot higher "14.4 A/F ratio". That means the car would never have a correct base line.

Tampa 928s

*So I'm not loosing my mind after all !
Hi Mark,

* No comments please!

Your unit was out of calibration.
I suspect the new driver we installed had a problem.
I replaced it.
Sorry for the problem with this unit.

Kevin