J

Jamiehol

Active Member
Driving to work this morning had an issue if under acceleration I try to hold the revs at 2.5k they yoyo smoothly between 2.5 and 2.3k.

If i accelerate past 2.5k I get a hesitation through out the rev range.

Before Christmas I had an injector fault which I fixed and reset the fuel trims, have probably done about 200 miles since.

Car is LPG converted but can't confirm it happens on gas as I ran out this morning, so far issue is only confirmed on petrol will get some gas today to check.

Car had new plugs and leads 10k miles ago.

I will get the Faultmate out tonight if I can face the cold.

But any thoughts or suggestions as to possible causes

Thanks,
Jamie
 
My last P38 suffered lack of power in mid range, it turned out to be a faulty MAF sensor. Changed it and it was like a new animal. One of those parts to change for the genuine article though, lots of cheap copies out there that aren't up to the job.
 
Yes the MAF had crossed my mind when I have got the faultmate I will do some data logs.

Based on previous pains with pattern MAFs on VWs I would only go for a genuine one.
 
I've got some known good figures for a 4.6 Thor. I'll dig them out when I get home.
Don't quote me but I think it was 20 kg hr on idle all loads off and ???? Dammit can't remember the higher one, I ll check..
 
Jamiehol said:
Driving to work this morning had an issue if under acceleration I try to hold the revs at 2.5k they yoyo smoothly between 2.5 and 2.3k.......
Click to expand...
If it was an L322 I would be looking at Gearbox/Torque Converter as when the Lock Up Clutch starts to wear when it is trying to engage it slips and then grabs then slips then grabs causing the revs to yoyo by a couple of hundred up and down....

Not saying that is your issue on the P38 (as they didn't suffer from the same problem as the L322's), but it could be something to look into if the Engine checks out....
 
Saint I hope to rule the gearbox out on the way home by getting some LPG and seeing if the issue happens on gas or not
 
Here you go, found them .....

Idle 680rpm - 22Kg
1200rpm - 32.5Kg
2000rpm - 55Kg
3000rpm - 92Kg.

Reading taken from very good engine and confirmed against my good one. I would like to take credit but that has to go to Eightinavee.

I thought about suggesting the TC as Saint has. Symptoms are as you are finding at a steady speed wavering rpms about 40 mph but this is on the ZF 5hp24 found on the L322
 
Rewmer thanks for the figures will take a log on the Faultmate on the journey to work tomorrow.

Did a test on the way home, ran on petrol and get the yo yo affect switch to LPG and it is rock steady, so I think that rules out the gearbox/TC as well as the ignition side of things.

Tomorrows plan is to run on petrol to work and log the MAF readings to file, journey from work reset adaptive values and again log the MAF readings.
 
I would just log the figures with the car static, AC off, lights fans etc. if she's ok on gas may suggest a fuel supply problem. Again from memory, I believe the line pressure should be 55 psi, but best check this in the Rave. Oh and don't believe your faultmate when it says the fuel pump isn't running, for whatever reason it reads back to front unless the lovely Gabriella at Blackbox has fixed the bug. Also note the Thor engines have the fuel pressure regulator integrated into the in tank pump rather than in the engine bay seperatly.
 
The reason I wanted to try logging the MAF readings driving was the issue doesn't seem to be apparent when the car is moving it will happily statically rev steadily at 2.5
 
I hear you. Would be a good idea to log the O2 sensors when it starts to miss behave. See if its going lean or rich and on one or both banks.
 
Yes did occur to me this evening over a beer that logging O2 sensors may be an idea, luckily outside work is a couple of miles of dual carriageway with roundabouts at either end which ideal for these sort of test runs.
 
Well what do you know, plugged the Faultmate in and logged the MAF data this morning, and I couldn't get the car to act up at all.

On cold on my drive, with the heaters on full blast to thaw the snow I saw the Faultmate logging the MAF figure as around 30Kg/s, going to plot the full run in Excel now.

Couple of flaws I notice with the faultmate, is that it doens't log RPM when doing data caputre on Fuelling, and you can't log more than one set of data at a time.

This is the first time I have really used it for data capture rather than resetting values or clearing fault codes.
 
Well after looking at the fuelling data in Excel i see once the engine has warmed up the MAF readings at idle are between 23.75 and 24.5 and the highest reading i saw was 290Kg/s whihc based on journey time would be during an acceleration phase on the Dual Carrigeway so highest load in the journey.

The fuel trims on both banks are close to each, and the average fuel trim is close to the actual fuel tirm.

Also looking tank fressure and filtered fuel remained the same throught the journey which I take to be good.

Going to log the o2 side of things on the way home and pray it acts up this time, haven't reset the adaptive values yet.

Thoughts or suggestions welcomed as before.
 
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