36 replies to this topic

[orcadian]

Does this new cam have anything which registers when it passes the cam position sensor, or is the ECU working without that info? Also I found the info about a company I dealt with in the early 90's, then called Camco 88. They are now known as Camco Automotive (http://www.camcoauto...ve.com/ecu.html) and might have an answer for you if they've seen the problem before.

[minimowta]

Hello again,
It sounds like you might be closing in on the problem - but just one question - when you shone the timing light at the bolt, did it go 'all over the place' on all cylinders at the 1500 rpm point or just one? Like you, I'm surprised that the Map test showed no resistance change - I will do the same test on my spare and report back. When I think more deeply about the 1500rpm bit and the Map sensor, you would really think that between say 1400 and 1600 rpm, there would be very little difference in absolute pressure, so the MAP sensor is surely not playing a part. Is there anyone who can properly test the ECU out there?

Hi there orcadian,

Thanks for your interest in my little problem!

I only shone the light on the bolt on one cylinder. Too dark now to try the others but I'm sure the result will be the same. I don't think my problem is down to one cylinder - I checked both sides of the coilpack with the strobe light as mentioned previously this evening and they both appear ok, I also tried those LED indicators on all cyls at the same time as mentioned a while ago and there was no missing flashes then either.

This misfire is most noticeable at 1500 rpm but it may also be there at higher revs, just not as noticeable. So it could be the MAP sensor stuck on one resistance is causing the problem - maybe this sensor has less impact at higher revs? Sure is a mystery!

That lambda sensor is still under suspision as well!

I know my experiments on the MAP were not very scientific but I really did expect some difference. It'll be interesting to see what you find.

Cheers

[minimowta]

Hi

There's a lot of complex testing going on here, but what about the cam? You mention a specific cam, and I assume this is not the standard cam? Some of the mini tuning books, also threads on the Forum, mention that some of the hairier cams can give poor idle and roughness at lower revs - could this be the problem here - especially as the ECU cannot b preprogrammed to suit special cam? Sounds like the motor runs like a dream at higher revs, so to be a bit brutal, is this actually a problem?

The cam is quite a mild road cam - a Swiftune SW5. I understand this gives more torque and a bit more HP. It certainly makes the car a joy to drive above 2000rpm and, anyway, this misfire I've got was there before the engine was rebuilt so there is something in the original setup which has transfered through unfortunately

I understand what you're saying about "is it really a problem" but my engineering principles won't let me accept it I'm afraid. It isn't right and I would like to know why! I'm a fussy "small piece of earth" I know Sorry!

Cheers

[minimowta]

Does this new cam have anything which registers when it passes the cam position sensor, or is the ECU working without that info? Also I found the info about a company I dealt with in the early 90's, then called Camco 88. They are now known as Camco Automotive (http://www.camcoauto...ve.com/ecu.html) and might have an answer for you if they've seen the problem before.

There is an injection and non injection version of this cam and I'm confident that the injection one has been used so I don't think that is the problem and, as mentioned just now, the misfire was there before the rebuild and just the same. We hoped the rebuild would make it go away....... It fixed everything else except this little teezer!

Cheers

[nicksuth]

You're not alone, many of us MPi owners have gone through the same or similar problems >

I changed virtually every sensor on my MPi when I had a misfire (more of a splutter really) when I was cruising and just feathering the throttle and it turned out to be fuel pressure related and after fitting a PBV and having it set upon a rolling road it cured the problem. When I took the old valve off it was obvious that the O ring had perished and was not sealing but was told I would have to buy the complete fuel rail as the valve is NOT a replaceable item - I reckon it probably is re-fittable after fitting new O ring, assuming you can get the right size and material???

I see you also have a PBV but no mention in the thread if you had it set up after you fitted it?

The manufacturer usually has it set at 2.0 bar as standard but if you have several mods (like mine) it has to be set while running up through the rev range. Mine ended up being set at 2.8 / 2.9 bar (2 x 1/4 turns from original setting) at tickover after several runs on the rollers. It now runs like a sewing machine (well, nearly) and I spent god knows how much on all those sensors !!!

PS - I have lots of part used sensors if you need to try them?

[lee_rob]

I hae exactly this same problem which i thought I had cured with a new lambda sensor. However I too have the constant misfire at around 1500 revs and the splutter if you blip the throttle. Is it worth hanging the original pressure regulator as I see you can still get new old stock ones from runner bros

[Fast Ivan]

4 year old thread dude.

start a new thread and we might be able to help