P38 Stumbling is back!

Hi guys,

Well the P38 has been behaving itself for a while now, but after a few longish runs my old stumbling problem is back.

It started off fairly gently as just a very occasional sudden drop in revs, but it worsened over time to the whiplash inducing stumble and surge buckaroo and stalling when stationary.

I'd assumed this was down to blocked fuel filter/crap in the tank, as it only seemed to start when the fuel was getting low and changing the fuel filter seemed to cure the symptoms.

I drained the fuel as much as I could and put a new filter on again, but the prob is still there.

Any suggestions appreciated (apart from torch it! )

Petrol/Diesel? Manual/Auto?

I have a similar but less violent problem with my DHSE. Never been cured however. Seemed to have started when I changed the fuel filter (is there a shrug shoulders emoticon?) It had previously overheated and had new rad, pump, stat, belt, tensioner, expansion tank cap etc, but that did not seem to be the start of it. Mine seems to be temperature related. As the engine is coming up to operating temp is when it occurs. I am about to fit a new engine coolant temperature sensor, so we will see how it goes.
good luck with it.

It's a petrol V8 auto.
I don't have any temp issues...have done lots of work on the car, new fuel pump and the fuel pressure is good.

If I put my foot down she'll push through the stumbling but it'll return quickly enough when cruising or accelerating normally.

Maybe some fuel cleaner? I have bought some biocide which is supposed to keep the system clean. I am going to try that as well.

Check your petro cap there is a vent hole in it for your tank to breath. When a full tank may not be a problem but 1/4 tank or there about will cause a stoppage like experience. ie Take a 2 liter bottle of liquid and turn it up side down and watch the liquid gulp or chug/ lack of air same as your petro tank. replace the cap

Thanks for the input guys.
Will have a look at getting another fuel cap, worth a try!

Originally thought it was just crud in the tank due to age, but have changed the filter several times so then thought it might be water in the bottom of the tank...draining it and refilling it in the pi**ing rain probably didn't help.
I had some seafoam left over so put that in the tank as it's supposed to absorb moisture as well as clean the injectors, no change though.

Hi, I can't comment on rr's but we had a lot of problems very similar to yours on Peugeots and most of them turned out to be air idler control valves or stepper motors. Cutting out or revs dropping on slow down or junctions lights etc.
Good luck

JD. said:

Thanks for the input guys.
Will have a look at getting another fuel cap, worth a try!

Originally thought it was just crud in the tank due to age, but have changed the filter several times so then thought it might be water in the bottom of the tank...draining it and refilling it in the pi**ing rain probably didn't help.
I had some seafoam left over so put that in the tank as it's supposed to absorb moisture as well as clean the injectors, no change though.

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Loosen your fuel cap and drive for awhile, and see if you can create the same problem. If it doesn't rear its ugly head then thats it. Also if your fuel caps hisses when you open it you have a vent problem

Vented filler cap? Thought P38s had a closed system?.... emissions laws. Stand to be corrected tho` not got RAVE to hand at mo`.

gtland said:

Vented filler cap? Thought P38s had a closed system?.... emissions laws. Stand to be corrected tho` not got RAVE to hand at mo`.

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If your fuel tank was not vented, then the fuel pump would put negative pressure(suction) on tank and collapse it (crush)

I repeat I`ve not got RAVE to hand here, but isn`t the system closed at the cap with venting via the charcoal filter in the "evaporative loss emission system"?

gtland said:

I repeat I`ve not got RAVE to hand here, but isn`t the system closed at the cap with venting via the charcoal filter in the "evaporative loss emission system"?

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Exactly right. But if it actually has a charcoal filter in the breather, it could be that. On my MR2 the EV emmision system caused all sorts of hesitation problems. Cut out the filter and bingo it cured the problem

john winsemius said:

Loosen your fuel cap and drive for awhile, and see if you can create the same problem. If it doesn't rear its ugly head then thats it. Also if your fuel caps hisses when you open it you have a vent problem

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My fuel cap has always hissed when releasing it.RR runs fine from full to empty(well almost) tank.(petrol 4.6)

Didn't think the EVAPs system would have that much of an effect on the system, something else for me to look at!

Interesting, I have the same problem with my 2000 Vogue 4.6, she kind of falters then picks up again. Interestingly I always get a hissing when I open the filler cap to refuel too.

Whats the school of thought on this, should it be vented or not?? Will it make a significant difference.

Hanoverian said:

Interesting, I have the same problem with my 2000 Vogue 4.6, she kind of falters then picks up again. Interestingly I always get a hissing when I open the filler cap to refuel too.

Whats the school of thought on this, should it be vented or not?? Will it make a significant difference.

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Get a new fuel cap. The vent hole is pluged and you are getting fuel starvation. To test loosen your fuel cap and see what happens when you take along drive.

Guys,

When I undo my Fuel cap on my 1995 4.6 I get hissing for a spilt second.

However on the cap it has a warning to firstly only slightly unscrew the cap to let the tank vent itself. Once the hissing has stopped continue to fully unscrew the cap.

Are we sure about replacing the cap?

Steve

:welcome2:hi jd , not sure this helps but worth a try ,i have a 4.6 v8 petrol with lpg and for last 4 weeks mine on start up i.e. petrol ran like a bag of **** , on gas perfect so i called up to emmotts of colne and young willie put another maf sensor unit on and it was like a new car so paid them and went home feeling very satisfied .my problem solved when i got home i stripped the old one down and cleaned it all up and using cotton buds and meths cleaned all 3 sensors on it , refitted it and result it works a treat ,, i know seeing all the threads mentions fuel problems but it might be as simple as maf sensor so can i suggest you get another from somewhere or if youv'e got a mate handy with same car whip his off and try on yours and give it a quick run ,this will only take 10 mins and at least you can eliminate the maf if its still the same ,,, best of luck n let me know how u get on ... p.s. emmotts of colne will ship one to you next day very reasonable price and great company to deal with ... kind regards MOZZ

Cheers for more input guys,

When the prob appeared I originally thought it was the MAF too, but have tried 3 MAF's and it's still does the same. After lookin at the symptoms I thought it prolly wasn't the MAF anyway as it judders more aggressively than just flat spots.

Have replaced the fuel cap (£7 is pretty cheap for the elimination process) and found a reasonable IAC valve so swapped that out too.
Pulled the EVAPS canister out, removed the carbon temporarily and cleaned the internal filters to see if it made any difference...

No difference! :frusty:

The fuel was just over the reserve so I'll fill her up and take her for a longer spin at some point this week.