base190380

Heres my problem, I have a rs turbo converted mk2 orion. Its a efi cvh from a 1991 fiesta rs turbo. ANyway car drives great and pulls really well but when decelerating, ie foot off of accelrator i get a backfire. I took it to rolling road and the guy says the cars running sweet when driving but when throttle closed the co pot takes over the fuel and air mixturue. He tried to turn it but it was making no difference to the mixture on his roller readings, and he says this may be knackered.

Has anyone else had this problem. Where can you get a very cheap co pot from so i can try another?
Thanks

MarkN

My Mk3 has been converted to EFi and has exactly the same problem. The emissions are correct and its had several co pots.

Problem is that it doesn't seem to cut the fuel properly on overrun, but then again is it supposed to?

base190380

okay anyone else no any answers to this?

base190380

Hi Markn, good to know you have the same problem, so that probley means ill waste more money if i buy a new co pot then. Any other ideas, or can you at least let me know what you find out. Do you think its still safe to drive like this?

Dragsteer

Maybe is co pot faulty, but I wouldnt bother with one bang if mixure under load is correct, and if co at idle is set ok. I have same thing, sometimes I have backfire when relase throttle but I dont think it is problem, my co is little higher.

base190380

hi, thanks but im getting backfires on overrun pretty much all the time when i let go of the throttle but never when driving under load. just on over run.

davsmith64

ok to set the co2 up on a efi car,, u cant just turn the co2 pot and expect it toalter, you need to get it on the code reader / computer to set it into service mode or summat,

well lane showed me this.

originalcabbie

I have similar problem on a MFI turbo anybody got any ideas?

(Sorry to HIJACK the thread!)

MarkN

My mixture is set up spot on by an exhaust gas analyser. There are no fault codes logged - it comes up all clear both from the instant test and KAM.

And it still backfires on overrun...

Dragsteer

MarkN: throttle position sensor click?

If you have bang only on lower rpms when relase throttle (1000- 2000 rpm) then this is conected with idle mixure (co) if I have right.

base190380

okay if i replace the co2 pot and its no different am i right in thinking it must then be the tps sensor thats buggered? I used one off of a unknown engine and its done it ever since i first started the engine after a rebuild.

Dragsteer

If throttle position sensor click after you start to move throttle then is ok. if I dissconect TPS then have little missfires from exhaust

MarkN

The TPS don't click on an EFi setup, - they use a smooth resistance change as it opens up.

Incidentally I've tested mine with a voltmeter and it is perfect - even so I still changed it and it made no difference.

The only other thing with mine is that it hesitates a bit when it is cold - like it has a flat spot. Does yours do this? If so it might be connected.

I begin to think it could be a faulty ECU or MAP sensor. I put a new MAP sensor on it and it improved the hesitation but didn't change the back firing...

MarkN

Come on SafeChav - I'm sure you must know the answer to this - or be able to make some sugestions.

I'll never take the piss out of your lump hammer again lol

base190380

would a faulty map sensor not bugger up performance when driving though? Im starting to get thoroughly pissed off now. It can be so annoying. Maybe ill need to source another map sensor and ecu

Chris69

is your idle and tps set right? i know this can cause overrun issues according to the frst manual.
i have had mine converted to efi by andy(safechav) and its fine, set the idle according to haynes and the CO's on a lambda probe and its smooth both hot and cold with no backfiring.
gott be something simple as the efi is pretty simple lol

MarkN

Strangely this problem only seems to affect OFAC and not OFAB (as far as I can tell) Do you know which you have chunt?

Chris69

I have OFAB, looks like its does lie within the the OFAC system then
chris

MarkN

This is wierd I've heard of three or four people having this exact problem and I can't get to the bottom of it. I'm quite knowledgable with EFi and did not expect it to be this hard to fix, but I've now changed everything apart from the ECU and ACT sensor (which I've tested with a meter). I am now thinking of giving OFAC the chop and boshing an OFAB on there instead.

The next step would be to try a new OFAC ecu - so I might as well get an OFAB ECU and MAP sensor instead and see if the problem disappears...

markc

is the ecu chipped?

hows she running mark

MarkN

Running pretty well thanks mate - goes really well compared to the n/a setup. There's just this annoying problem to overcome - I'm sure its something simple but I can't find it

base190380

okay im running the ofac ecu with matching map sensor, so maybe the ofab is the way to go but i cant be arsed changing the ecu and map sensor and wiring mods. I know its easy enough but would rather stick with ofac setup. Anyone else have any ideas what causes this

Fiecos Dan

if your back firing on over run, its running lean on over run, which is not a problem.

markc

good stuff would be good to see how well shes running. bet u have had some fun in it

base190380

okay then, anyone else had problems with ofac ecu going faulty like this, or am i starting to look in the wrong direction?

Fiecos Dan

a vacum leak is a common fault.

Reeve69

A bit late reply. I know it sounds daft but change your fuel filter! It's starving of fuel running lean either that or fuel pump could well be on of your injectors are knackered one could be dripping when you let off. Hope this helps I had exact same problem did the 3 things and it solved it. Also when holding the revs at 3000rpm it use to pop like mad!