V8 EFi missing under load.

Hi I am having intermittent ignition problem with a 1989 3.5 Efi V8. On starting - whether warm or cold - the engine spounds OK but, as soon as you put any load on it the engine becomes lumpy - sounds and feels similar to when you wrongly connect two of the ignition leads. However the lumpiness usually dissapears after a short bit of driving. I have replaced coil, HT leads, ignition amplifier and dizzy cap to no avail. I have a new condensor on way.

Anybody else got any ideas???

Graeme

Reply to
Graeme
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Air leak maybe?

Reply to
aghasee

Make sure the leads are routed correctly, especially on the left bank. Front to rear in the 4-lead clip, they should be 1,5,3,7. The reason for this is the firing order, 1-8-4-3-6-5-7-2, no's 5 & 7 need to be kept apart and not run parallell together or you get a phenomenon known as cross-firing, (which is pretty much as you describe your fault symptoms), where the emf from one lead is induced into one next to it. As long as one lead crosses over another, any induced emf is cancelled out (or something like that), so no's

5 & 3 cross at the plugs. Badger.
Reply to
Badger

I had this on mine - turned out to be a seized centrifugal advance mechanism. The split diaphragm in the vacuum advance didn't help much either... take the vacuum pipe off the carb with the dizzy cap off and give it a good suck - you should see the mechanism move and release when you stop. Also check that the rotor arm can turn for a few degrees against spring pressure and releases freely. On mine it was lumpy until you had gone over 2700 RPM once and then cleared due to the advance finally swinging round. Don't think you will have a condenser on an EFI vehicle as it has electronic ignition - no points in the distributor!

HTH

Jon

'94 RR Classic '78 SIII Lightweight

Reply to
Jon Robson

Apologies for the late reply... thank you all for the input - I will give all the suggestions a go in daylight over the weekend and see if they help (and I do have a condensor fitted to this one - weird?)

Chief suspect at the moment is the timing advance as it feels just as though the timimg is retarded too much when you try and accelerate uphill. All the leads are routed correctly as I had lots of fun out there with a torch a few nights ago and the result is an exemplary run of leads - makes a change for me as they usually look like spaghetti1

Thanks again

Graeme

Reply to
Graeme

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