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Help with engine start

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Hi all,

I'm trying to get my TVR straight six engine started on a new Haltech Elite 2500 ECU but am running into problems. When trying to start it spits/backfires through the ITBs which I took to suggest the timing is out of whack. But having checked the TDC angle with a timing light and checked the wiring to the coils with a multimeter everything seems ok.

I've tried adding 360° to the TDC angle and also varying the ignition table from 15° but nothing seems to work.

The really weird thing is that I had the engine running initially, albeit very poorly, when the firing order was incorrectly set. I then changed it after checking which order the intake valves open when rotating the engine by hand but now it's worse and won't even start.

The engine was mechanically sound and running ok before installing the ECU. The other things I've changed are moving to coil on plug from the old coil pack and also added a DBW throttle actuator for the ITBs.

Is there anything other than the timing being out that could cause this? Or some other way to verify the timing is correct? I checked the TDC angle with the timing light connected to the lead for coil 1, could this give an incorrect reading given it's coil on plug?

Any help or ideas where to look would be much appreciated.

Cheers,

Jon

Are you sure it's wired correctly? Some ECUs you wire in cylinder order, and some in firing order? Cylinder 1 will always be correct, it's the other cylinders that are likely causing your backfire...

Hmm that sounds like it could cause the problem. Although the Haltech diagram says to wire the ignition outputs to the cylinder number which I took to mean cylinder order. Will check it tomorrow.

Don't forget to also check the injector order.

Have you tried to increase cold start and cranking fuel?

Yeah did I try increasing the fuelling but it didn't help. Would lack of fuel at cranking cause the backfiring then?

Usually it's wrong firing order that causes backfireing. Lack of fuel or excessive fuel can cause it too but if the engine is not cranking at all that's a sign of wrong wiring...

Pull the spark plugs and see what they look like - white insulator with a wet/shiny look on it usually means fuel but no ignition, black insulator with a wet/shiny appearance suggests it's firing intermittently and/rich, dry white suggests it isn't getting fuel, dry sooty look suggests rich and firing consistently - but those are just guidelines, and there are exceptions.

Is it actually back-firing - through the inlet, or through the exhaust?

Other things can be cross-firing through inductive voltages in the leads, or hung up/incorrectly set valves. A poor mixture can cause it if the fuel is burning slowly, after ignition, and when the inlet opens it ignites the charge there - in some cases it's because the exhaust is back-feeding unburned charges through the exhausts.

Something you could try is to disconnect the injectors, and try starting it with some engine start, brake clean, or other flamable substance delivered directly to the throttle intake. If it starts cleanly, it's most likely a fuelling problem.

Finally found the problem.

I ordered a spark plug extension and put the timing light clamp on that rather than the lead before the coil. Cranked the engine and voila, it was 240° out.

It must have been picking up the signal from the coil on cylinder 2 that it was next to. Lesson learned I suppose.

Thanks for the help everyone.

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