Just when I thought my car was beginning to run well I have a problem which is driving me mad. I have put in new leads, extenders and plugs had the cam belts changed and the Mondi was running very well indeed! A few days ago my car started running strangely, it backfires when revved in neutral. This sounds like a muffled backfire (a 'foom' rather that a 'bang' if that makes any sense?). It seems to run okay at constant revs but doesnt like fast revving/acceleration. I have taken out all of the plugs and cleaned and regapped them and I am about to test the continuity from the extenders to the dist caps to check these are okay. I am also going to drain the feul in case when I filled up at Shell they sold me some duff tractor gas. Any ideas what this might be would be very greatly accepted as I am going round in circles with this one. Frank
Yep, This started on a run when I took off from a roundabout with one backfire, and then when I got home I found that when I revved it in the driveway it complained. At constant revs (say 3000) its smooth enough. I think if I had the leads swapped I would have it trying to tear itself apart and a constant backfiring. Frank
I got my wife to rev it up (in a manner of speaking) while I listened and it is firing back through the aircleaner (hence the FOMM rather than bang). I suppose it could be a number of things but before I say 'valve spring' or anything else REALLY expensive I was looking for cheap checks first. I was going to drain/replace the feul but cant work out the best place to drain it off. I cant get a hose down the filler it seems to take too many kinks and turns. I would try the feul lines but that may overheat the feul pump. Distributor caps are no longer available so hope its not. So whats the best way to drain the feul? Frank
There are two fuel tanks with a single cover plate (about 3ft long and 18inchs wide) undo the cover plate and you'll see that each tank has a 19mm drain plug, have you pulled the plugs out to see if any of them asre foweld up? It could also be that the timing is out following the new belts Regards
I subscribe to Andrews line of thinking to some point, firing into the air filter is usually a timing issue, I would find it strange however to think that the valve timing is out. I would go for a Compression test, burn valves are now on my list, but check caps and rotas first ! Good Luck
The caps and rotas look okay. I managed to drain the tanks and went down and got some Optimax to try and check this out first. It just seems like a big coincidence that this started 10miles after filling it up. I will try the compression test next. How do you check/adjust the timing on one of these? I am okay with a 'normal' distributer and a timing light but where do you adjust these with 2 distibuters bolted to the head? Frank
I do not think you have an ignition issue. I believe that you have a lean mixture in one or more cylinders. This is a classic symptom of it. Because this is an injected car, I'm going to bet you have a plugged injector. Pull all the injector nozzles and soak them overnight in carb cleaner. Blow them dry and inspect. Re-install. Then run a half tank of fuel with Techron fuel injector cleaner through the car. You would be surprised how well this stuff works. (Techron is the only brand most Fchatters endorse). It is very typical to get "popping" through the intake when the mixture is lean. (We carb guys know this stuff!!) With carbs we usually clean and adjust jetting when this happens, but with FI it's almost always a clogged injector. Best of luck. Birdman
Thanks Birdman, I drained to feul out and put some Optimax in from a different petrol station and drove it hard for a few miles home to flush it through and I am sure that the car is a bit happier. There is still a slight misfire through the air intake on revving but not as bad. A tank of bad gas may have made an existing problem worse. I will take the injectors out as you suggest. It looks like the feul line unscrews and the injectors are underneath and should just unscrew (hopefully no surprises or special tricks required here). Will a visual show if they are clogged? Do I need new seals or anything before I start? I dont know if Techtron is available in the UK I will ring around tomorrow. I did put some other FI cleaner through the system a couple of hundred miles ago as a preventative measure but maybe that wasnt man enough for the job..... I am also a lot happier with carbs, this FI is black magic indeed! Frank
i would also consider replacing the fuel filter as soon as possible. if trash got into the injection system, or if its water contamination in the fuel, the filter should be changed as it is the first line of defence.
