Hot running problems

This is going on from my previous thread

http://www.landyzone.co.uk/lz/f42/ignition-likely-cause-problem-145286.html

I've now determined that's its definitely not anything to do with ignition.
The problem is that when the engine is hot, it will start on petrol okay, but it will then not rev much past 1000 and will cough and splutter and then go back to normal idle. If I then leave it say 20 minutes or so it will be cool enough and then run okay. Not sure for how long cos I switch it to lpg as I've only got a small petrol tank.

I know my vac advance is gone, got one on the way, but that has been gone since I've had it and this problem only started at the weekend.

The temp sensor was replaced when I got it, with a Intermotor part, which I've read on another forum they are okay? And the afm is also reading 300ohms across the 2 outer pins.

Anything else it can be? Are there tests I can do on other sensors, what readings should I get? (Don't think my old rrc haynes shows anything about it)

I do plan on getting a diagnostic test if I can't solve it but wanted to see if anyone had any ideas before I go spend the cash on that.

Fuel pump failure due to run low on petrol!
As you have gas I take it you run a low amount of petrol in the tank as when on gas the pump is still running even though you are running on gas thus as the fuel pump is cooled and lubricated by the petrol when going round a corner the low fuel moves away from the pump and runs druggie buttering up the fuel pump

Option two does the disco have a one button remote or two?
If it has two it could be a duff spider unit

It's the two button remote but I've already bypassed the spider.

I would have thought if it was the pump it would do both when its hot and cold? The petrol tank was low, about quarter of a 25 or so litre tank, when it first started so I guess that would make sense.

I've just fitted a new idle stepper and it wont idle, it's defiantly working had it out and can see it moving, but with the old stepper which doesn't work it will idle, would this mean that the base idle needs setting? Looked up how to do it on rave but wanted to confirm before I messed around with it.

gooselogan said:

I've just fitted a new idle stepper and it wont idle, it's defiantly working had it out and can see it moving, but with the old stepper which doesn't work it will idle, would this mean that the base idle needs setting? Looked up how to do it on rave but wanted to confirm before I messed around with it.

Click to expand...

Yes to check/set base idle.

I would also suggest you remove and clean the plenum (if you haven't already) and check/set the throttle disc.

BTW I would agree with vougese39 - low petrol level will cause the sort of symptoms you describe.

You say the MAF is set to 300ohm - I understand this is only a base setting - check the CO and Fuel trim values as well. If you have cats it might be worth checking the lamdas are working properly as this could also affect running.

If the vac advance isn't working you are likely to get poor throttle response. Make sure you check the ignition timing and set it BEFORE you set base idle but also remember to adjust it for the LPG (can't remember if it needs to be slightly advanced or retarded).

classic kev said:

Yes to check/set base idle.

I would also suggest you remove and clean the plenum (if you haven't already) and check/set the throttle disc.

BTW I would agree with vougese39 - low petrol level will cause the sort of symptoms you describe.

You say the MAF is set to 300ohm - I understand this is only a base setting - check the CO and Fuel trim values as well. If you have cats it might be worth checking the lamdas are working properly as this could also affect running.

If the vac advance isn't working you are likely to get poor throttle response. Make sure you check the ignition timing and set it BEFORE you set base idle but also remember to adjust it for the LPG (can't remember if it needs to be slightly advanced or retarded).

Click to expand...

I've taken off the plenum and cleaned it this morning, the throttle disc fully closes. I've also made sure the vac outlet for the vac advance is clear, think it was blocked before. The vac advance is working now aswell, changed that yesterday.

How do I check the CO and fuel trim values on the MAF, and what should I be getting?

The ignition timing is set to 6deg but looking at some searches on google LPG should be a couple degrees more advanced so I shall do that once its running again.

Success, I've done the base idle, and its now idling perfectly, it was quite out. I think all the vac leaks were keeping it alive before

I shall get a new fuel pump ordered and hopefully that will solve the last of the running problems.

Then just all the brakes to change and ABS to fix

Sounds so easy

Mr Noisy said:

Sounds so easy

Click to expand...

It's not, although it's not the hardest thing I've had to do on a car


Changed the pump, runs better, revs right to the limit which I never used to do. Left it running to warm up, it starting doing the business again.
But I remembered I hadn't actually put that much fuel in so dumped another 5 litres in and it was fine!

Luckily I cleaned all the crap out the tank so hopefully nothing has gone and ruined another pump.

The old fuel filter, which I had only changed a few weeks ago had alot of brown petrol coming out


Going to go fill it up now and see if it behaves itself.



Cheers vougese39 and classic kev, I owe you guys a pint

Turns out, it isn't fixed. Still won't run when it's hot. What else could it be?

It's the MAF, unplugged it and it was fine.

gooselogan said:

It's the MAF, unplugged it and it was fine.

Click to expand...

It will run but it will be very rich (about 6mpg) as the ecu will default to the limp home fuel map. If you are happy it is the air flow meter then get a replacement and then adjust as necessary but be aware an ECU fault could also do the same. I had one - plugged in the diagnostic said ecu not reading air flow meter; it turned out the problem was the ecu and not the the MAF. If you can get hold of one, try plugging in a substitute ecu and see if that sorts it.

I'd pay someone to check out the sensors before you replace anything else.
Cost me £35, with someone who had access to Autodata on the computer.
The problem you have affects both petrol and lpg.

I'm fine with it running at the moment, aslong as I can get to and from work.

As you suggested wookie I'm going to get it plugged in and then go from there. At least I can get the thing there now.

Just a word of running without the Afm long term it will cause bore wash then you will have a fubar engine
Got two p38 with major oil consumption faults caused by failed Afm and lambda sensors!

Thanks for the warning, earlier I twisted the afm pins slightly and put the plug back on and after leaving the battery unplugged for a while it seemed alot better. Pulled like it should when driving, before it seemed fairly sluggish. So I'm wondering whether they were just bad connections. Shall see what its like over the next few days.

there was a issue with the afm and a modified connector with gold pins was used but still had the stutering fault make sure the pins and clean and DON'T! use an electrical contact grease that is very bad

I'll give the pins a clean with some tiny fine files I've got.

I've found today that when I start from warm if I press the throttle straight away it will rev properly and then switch to gas but if I leave it then it won't run and the idle hunts around a fair bit. Also, if normally I switch back from lpg to petrol whilst it is running it will idle very low and generally cut out.
Could this give anymore indication as to what it could be?

you really need to get the ecu fault read to see if it is a afm or throttle pot sensor fault guessing is not always the best way

I plan to at the weekend, I was just wondering if it could be narrowed down at all so I know how big the bill is going to be

Cheers