Rough running 1999 4.0

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nickdp

New Member
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6
Hi, hoping for some thoughts on my engine woes.

I have a 1999 4.0 Thor running LPG, I have owned for 3 months and it ran like a clock. Couple of weeks ago it started 'missing' every now and again on both petrol and LPG, has got progressively worse. Seems to bog down and will not accelerate.

Currently it is very intermittent can run for miles without issue then runs pants.

Things I have done
Changed plugs correctly gapped for LPG.
Checked for air leaks.
Cleaned throttle body.
Changed air filter.
Found damaged O2 sensor wire and fixed.
Cleaned LPG injectors.
New LPG filter.
Two tanks of petrol injector cleaner.
Cleaned MAF sensor.

Observations
Doesn't seem to be running rich no excessive smoke and plugs looked OK when changed, too lean?
Ht leads seem pretty new.
Seems to run fine over 3000rpm.
Same problem when run with MAF disconnected.
Slightly worse on LPG.
Very occasional backfire.
The alternator is making some noise but sounds like bearings.

Trying to avoid costly garage visit and learn more about my car.

Thanks in advance
 
Thanks for the advice, as soon as I can figure out this app I will do it properly but for now, I am just outside Edinburgh, Scotland.

Yeah sorry for the giant post just wanted to make sure I got all the detail in.
 
Don't discount the MAF just because you've cleaned it (cleaning it rarely works). I had the exact same symptoms a few weeks back with mine & did most things you've done. Changed the MAF & all ok. I did take a punt & bought a new Bosch MAF without diagnostics first which is not advised TBH. If you can find a helpful member nearby who can lend you theirs then this would be the best route.
 
Thanks for the thought,
I have considered probing the MAF to look for fluttering signal and compare the voltages to a 'standard' table I found somewhere.
The reason I haven't yet is I ran it for a couple of trips with the MAF disconnected, which to my understanding should mean a default fuel map based on throttle position is used, normally giving slightly rich fueling, and the problem was still there. So this made me think not MAF.
Should I test the MAF anyway?
 
Have you got diagnostics?

I'm in Edinburgh too so happy to plug the nanocom in to check if that helps?
 
Domino, that would be great don't think my trusty multimeter will get me too far with these fancy electrics[emoji4]
 
Met up with Nick today - nice chap!

So, got it on the Nanocom and it came up with the following:

NANOCOM - MOTRP38.APP - MOTRONIC fault file

P1668 = ANTI-THEFT ALARM SERIAL
LINK FAULT DRIVE CYCLE A
OCCURED 1 TIMES
SIGNAL TOO LOW
FAULT IS CURRENTLY PRESENT
FAULT DETERMINED AS PERSISTENT
FAULT DOES NOT CAUSE THE
MIL LAMP ACTIVATION

---

I cleared that all off just in case it was stored from anything previous and re-read the codes. Then received this:

NANOCOM - MOTRP38.APP - MOTRONIC fault file

P1000 = LAMBDA SENSOR UPSTREAM
CATALYST BANK 2 DRIVE CYCLE C
OCCURED 1 TIMES
SIGNAL MISSING
FAULT IS CURRENTLY PRESENT
FAULT DETERMINED AS PERSISTENT
FAULT DOES NOT CAUSE THE
MIL LAMP ACTIVATION


A bit more digging was done in so far as reading various sensors and we discovered:

- 1 misfire on cycl 8. Total misfire count was 1.
- Lambda sensor readings. Lambda Bank 1 was changing in live data, Lambda Bank 2 didn't shift from it's base reading... .44 or .99 I think it was, can't recall.
-HEVAC outside temp was reading about 10 degrees too high.
- There was a section in Motronic outputs regarding "Temperature" and "Internal Temperature". Both read 44/45 respectively. Not sure if that's in any way relevant.

The engine is running quite a lumpy idle with noticeable movement every few seconds when the revs dip slightly.

Hopefully someone can help Nick out... as all I could do was read off the wee screen! :)
 
Right misfires on petrols I can deal with, You say it's on Cyl 8 and it happens on both fuels. Have you done a compression test ? MAF sensor is that linked into a LPG system ? I presume this is a fully digitised ignition system, in which case no distributor. As on the classics they suffered from a worn bearing and the points or spark gap altered. Mind you a modern system can jump a long way. Lambda sensor would normally affect only the petrol system. Sometimes the injection holes for the LPG are through bungs which harden over time. Run the engine on LPG and use a little squirt right near to the injector of carb cleaner, note the engines revs. they shouldn't pick up, if they do then the hole is leaking. Keep carb cleaner away from the HT leads. Spark plugs tend to look almost clean now days, a white powdery looking deposit is a indication of a weak or ignition fault. But spark plugs also have resistors built into them now and tend to jump the bad section in the ceramic section. I check them with the multimeter on 2K or higher.
"P1000 = LAMBDA SENSOR UPSTREAM
CATALYST BANK 2 DRIVE CYCLE C
OCCURED 1 TIMES
SIGNAL MISSING" = Misfire
 
Last edited:
Many thanks to domino for the technical wizardry.
The outside temp calmed down for the trip home and read a much more realistic 14.
tnseal -
I have not done a compression test, but I would expect a high miss fire count and it not to be intermittent if caused by compression? but we can add that to the to do list.
I have looked for air leaks with the method you suggest and could not find any.
Spark plugs are brand new so they will be OK.
You are right there is no distributer, my understanding of the LPG system is that it does use all the inputs that the petrol system does.

When I take the revs above 3k it seems to run fine, I have read that this system runs open loop at this point which would support one of the feedback sensors being an issue.

As we were able to see today that one of the lambda sensors was definitely not responding I think that will be what I replace next.
 
nickdp said:
Many thanks to domino for the technical wizardry.
The outside temp calmed down for the trip home and read a much more realistic 14.
tnseal -
I have not done a compression test, but I would expect a high miss fire count and it not to be intermittent if caused by compression? but we can add that to the to do list.
I have looked for air leaks with the method you suggest and could not find any.
Spark plugs are brand new so they will be OK.
You are right there is no distributer, my understanding of the LPG system is that it does use all the inputs that the petrol system does.

When I take the revs above 3k it seems to run fine, I have read that this system runs open loop at this point which would support one of the feedback sensors being an issue.

As we were able to see today that one of the lambda sensors was definitely not responding I think that will be what I replace next.
Click to expand...
New plugs that are duff are not unknown.
 
Update,
Being away for a weekend and a ridiculously long delivery on a new lambda sensor have delayed me but I now have news!
It might be fixed....
Checked the spark plug in 8 compared to 2, all good. Fitted new lambda sensor and took it for a test drive(petrol only) and it felt like a different engine.

Thanks everyone for all the help
 
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