I'm trying to figure out why my D1 GEMS engine appears to be running rich.

I get a rich smelling exhast, I see the LTFT is dialed back up to -19.5, and my O2 sensors are frequently reading around 1.0V.

I've done what I could to rule out a faulty MAFS. I'm seeing the really low values for g/s that are mentioned in other threads, but it does appear to be working as the reading increases with engine speed.

I had a faulty upstream O2 sensor a couple years ago and replaced it. At that time, it was reading like 0.10V and would not change as the engine ran. Now all four O2 sensors are active and their voltage varies from 0.0V to about 1.0V. However, I notice that all of them frequently read near 0.9 or 1.0V when the engine is running. They sometimes dip lower, but not for long. I wonder if I should replace the other upstream sensor, but I don't think this is the cause of the rich running.

I have good fuel pressure (new pump last Fall), and I believe the fuel pressure regulator is working. The vacuum line is tight and I can see a difference in the sensors when I disconnect and plug the vacuum line. So I believe it is functioning.

I could have leaking injectors. I haven't seen anything obvious on the plugs.

My Tank Pressure Sensor may have failed earlier, before I replaced the whole sending unit.

My Throttle Position Sensor is ranging from about .10 at idle to .89 at WOT, so I believe it is working normally.

I cleaned the MAFS twice now, and I cleaned the intake around the TPS.

I'm not getting any codes.

 

Since nobody has touched this one yet, I'll give it a go.

Too much gas, is either making its way into the engine on it's own, or the computer is putting too much in. Since you sound like you are capable, I assume you have eliminated the first possible cause. (Leaking injector, malfuntioning FPR, large post MAF vacuum leak)

I can only relate my own experience, and what solved it. I too, had ridiculous negative LTFT. In short, it was the MAF. The MAF has its own cleaning cycle, and is extremely fragile and should never be cleaned, irregardless of what CRC would have you believe. If there is something stuck on there the the burnoff cycle can't deal with, it is toast anyway.

Truck is running great, last tankful was ~ 14 mpg, a bit better than it has been for a while. The LTFT takes a while to update, haven't looked where they are for a while, she is down for the moment b/c the stupid plastic drivers side door handle broke off (anybody got an extra, lol) and I'm sick of crawling in through the passenger door.

I'll take her around the block tonight and report back where they are .

 

Thanks. I am curious where your LTFT is now. I read a lot of threads on the MAFS, but I was unable to conclude how to test it. It seems there is agreement that the Land Rover GEMS ECU does not report the MAF g/s to ODBII correctly, so the ODBII readout appears to be useless in testing other than to confirm there is some kind of signal or not.

I can try replacing the MAFS, and just see if it runs better or the LTFT starts to go down.

It doesn't run horribly, but it's low on power and sometimes won't downshift going up a hill. There's times when I struggle to go over 60 up a grade unless I manually downshift and get the engine roaring just to make it to 65. Needless to say, the fuel economy is poor. I'm not expecting big HP or many mpg, but the LTFT hit -20 today and it's running like its rich. I'm convinced there's a simple fix that will make things so much better if I just found it.

 

Drove it to work today. Here is what I observed.

Both LTFT are at -19.5. The STFTs which before the MAF change out were always negative, and close to 9 or ten, except at idle, ~3 or so, they now vary in synch with throttle input and road conditions. Jump on the gas, they go negative, and max out around -12 or so. Long coast with no throttle input, they go positive, maxing out at about the same levels. Sitting at idle, they drift around, positive and negative, for the most part -1 < x < 1.

Truck is running fabulously well, with the tiniest of a stumble (not even a stumble, really, 1/10th of a second before power hits) off idle I think I need to check my TPS, maybe clean the throttle body.

 

This may help... When my MAF was bad it did not run well at all. Unless you unplugged the MAF after starting. Then it smoothed out.

 

I replaced the MAF with a new one. It runs the same and the LTFT is still somewhere between -18.0 and -21. I don't think there is anything wrong with my original MAF.

Instead, I suspect that it is normal for GEMS engines to run with high negative LTFT. If anyone has a GEMS motor reporting a lot higher LTFT like close to zero, let me know please.

 

What scanner are you using? And is there a LTFT and LTFT2 showing up on yours?

I wrote down my LTFT2 value by mistake. Which was 1.6% after about 30 mins of driving and engine up to temp.

 

Ultraguage. Yes, I have STFT for Bank 1 and STFT for Bank 2, as well as LTFT for Bank 1 and LTFT for Bank 2.

Both LTFT values stay identical, but move between -18.0 and -22.0.

STFT varies a lot but is consistently lower on Bank 1 vs. Bank 2.

I have two good/new/low-mileage O2 sensors in the upstream positions now.

I don't know what else to do. I will probably have to pull the injectors, set up some plastic bottles, and do a leak test and a fuel delivery test.

 

Good luck. Let me know if there is any other values from my ODB2 I can read for you. I have noticed there is a lot of information on my 96 that seems to missing on the ODB2 which is a bummer.

I would also like to hear if you found a solution.

Cheers.

 

I decided to pull the injectors and check for leaks. I pulled them out of the manifold but left them on the fuel rail. I put plastic bags on each injector and pressurized the rail with the fuel pump. I did not see any leaks at all after several minutes. Then I cranked the motor over for one minute. The bags filled with a few cc’s of fuel. I measured the fuel from each injector and they were consistent. I measured by weight so I didn't have to transfer the fuel to a graduated cylinder or anything, just weighed it in the bag. It was good enough to tell that there wasn't one or more injectors that were sticking open too long.

So I doubt the fuel injectors are the issue. I still wonder why I have what seems to be extreme negative LTFT, and uneven STFT from Bank1 vs Bank2.