Mystery car problem

[westhamtim]

First up, Bibs - I've posted here rather than the V8 technical forum as I'm perhaps not just after technical advice and I'm also not sure if the problem is specific to a V8. If this needs to be moved, please feel free!

Right, further to the post below:

http://www.lotusespritforum.com/forums/ind...15&start=15

..my car has been sat at a garage for just over 4 weeks now and I really need some help and advice.

The problem started as a small shudder under high revs and deteriorated to a situation where the engine sounds rough after 2 minutes or so of running (it starts fine and runs well for those two minutes before the left exhaust starts popping). I was previously concerned with the cat glowing red but now assume that this is due to unburnt petrol combusting in the cat and is a symptom rather than a cause. The MIL light has not come on. The car went to the garage at the start of the year and the problem was diagnosed as two cylinders not firing. The garage tried to solve this by replacing the coils and plugs (and perhaps the leads). This didn't solve the problem so the garage thought the problem must be the ECU. This was sent to a specialist on the south coast who couldn't find anything wrong but, I believe, replaced the ignition circuit.

When the car was next started it seemed to run fine and this was the case for 60 miles or so before the problem came back. The car went back to the garage where it was checked over. They again arrived at the ECU being the problem and sent it back down south where nothing was found to be wrong. A second opinion was sought and the ECU was sent to Blue Streak who confirmed it was fine. The ECU was returned to the garage about 2 weeks ago and there doesn't seem to have been any progress since as they dont have any ideas as to what's wrong. I can hardly take the car elsewhere as it would need to be transported there and I'd end up paying for any new garage to go over the steps that have already been taken.

So I think my questions are does anybody have any ideas as to what may be wrong, and does anybody have any advice on what I should do next? I've always had full faith in the garage and trust the guys there but the lack of progress and lack of any apparent way forward, as well as not having my car is leaving me frustrated.

Many thanks in advance.

Cheers

Tim

[cjtpb13]

Tim,

RFI:( Request For Information)

Have you pulled the plugs to look to see how each cylinder is firing? To see if there is any excess unspent fuel on them. Reason why I ask, I once had a similar issue; turned out a brand new #3 lead had been torn at the insulator boot and as it moved around the insulation would split open and the spark would jump over to the block causing a stumble. I had pulled the plugs and saw that there was excess fuel on the plug which made me backtrack everything and discovered the tear under the plug boot.

[billt]

You need to isolate the bad cylinder(s). When it's running rough look at the RPM's on the tach then remove 1 spark plug lead at a time - a good cylinder will cause the RPMS to lower but a lead on a bad cylinder will have no effect on RPM. If the mis-fire seems to drift from cylinder to cylinder I'd first look for a distributor problem such as a bad dist. bearing. A cracked dist cap can cause your problems. If cars no longer have distributors then it's been too long and I'm too old to be giving advice. I believe it IS electrical however - gas IS getting to the cylinder but it's not burning.

[mayevora]

My ECU was sent to Blue Streak 4 times last year - each time they said it was fine. It turned out it wasn't, it was the fact they were unable to diagnose and reprogramme properly and as they seem to be the only people who can do this, I ended up getting it replaced with another V8 ECU (unfortunately very rare, and now seems to be vertually impossible to find good working V8 ECUs)

Not much help Tim I know, but good luck anyway.

[peter_england99]

Hi Tim,

I'd ring round for a garage that has a spare 'known working' 98 onwards ECU. Then they can put it in the car and prove if its the ECU or not.

I presume that in the time your car has been with the garage, that they have been able to eliminate the blocked cat theory.

Have you had a chat with Lotus's tech support guys?

Regards,

Peter.

[Nautilus]

Perhaps a blocked / collapsed cat?

fine whilst cold but once it starts to warm up & expand the whole thing bungs up? Try running a straight through pipe or hollowed out cat or similar to see if the problem reoccurs.

[westhamtim]

Chaps

Thanks for all your input. The garage already know which cylinders are causing the problem and I've checked and new leads were put on. They are still convinced it's the ECU and have now taken it apart themselves, isolated what they think is the problem and gone back to the ECU guys. So Ian your comments are maybe definitely useful! It's still frustrating but at least now there is another lead and a potential way forward but of course we lose so much time everytime they have to send the ECU off and wait for feedback. And now the weather's getting nice and I really need to go for a drive!!!!

Cheers

Tim

[billt]

Tim - One more thing to consider. ECU's in general don't shut down 2 cylinders but are more apt to shut down all 8 or at least make all run crappy. Don't rule it out (extremely weird things can happen) but since you have compression and gas to all cylinders the only thing messed up is the spark to a few of them. The ECU has to know when cylinders are near top dead center and they know that using the Crank Angle Sensor located on one left and one right cam. Your left one may be going bad. When cold it may operate OK but not when hot. When you get the ECU back and in case you still have the problem when hot go to Radio Shack and get some Kool it spray, spray it on the left CAS and see it it clears it up temporarily.

[westhamtim]

Thanks all for your feedback which I've passed on. The garage were still sure the problem was with the ECU and have taken it apart and traced the current through to find out where it is breaking down. They sent this back to the ECU specialists who have apparently fixed it (although it's unclear as to exactly what they have done!). So I'm picking the car up tonight! Fingers crossed it doesn't give up again as I'm taking it straight out on a longish journey as I'm away for the weekend. Cannot wait to see the car - it's 7 weeks today since it was dropped off.

Hats off to the garage who dont want any payment for the additional time they've put in until I've done a few hundred miles and am happy that the problem has gone.

Cheers

Tim