Thread: Mystery misfire
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Old 2nd July 2015, 09:45
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MartinClan MartinClan is offline
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I have fitted the new LP pump. And - what a surprise (not) - the HP pump is much quieter in that you can no longer hear it. (Just as when I first built the car.) Fuel pressure looks healthy - as one of my efforts in diagnosing the problem I have a tee fitted for a fuel pressure gauge. I hope I haven't damaged the HP pump as I already replaced it once when first starting to trace the problem.

So far the damage to the wallet has been:
HP pump, filter and non return valve (£££)
Crank position sensor (£)
Coil (Borrowed from Peter)
ECU (££) actually would have been (£) but I bought the wrong one first time - oops.
HT leads and distributor cap (£££)
LP pump (££)

I discovered the LP pump problem just after I bought the HT leads and distributor cap which is a bit of a bugg€r. I haven't fitted them yet so they could well end up on Ebay.

On the plus side I found the coolant leak that I have had since the car was first commisioned, and the coil is now mounted in a far better (cooler) location. And the new fuel pump had a big note with it saying it was E85 compliant.

Drove to work this morning. I didn't experience the big missfire but I still not convinced things are 100%. As I started to suspect, and the reason for it being so difficult to diagnose, there may have been two problems. Which means there still is one....

Tomorrow I have a longer run planned - weather permitting.

Cheers, Robin

BTW - I checked the old LP pump (4th time!) and it is definitely US. This time I just did it the simple way of wiring it to a battery. I checked the new pump before I installed it and I discovered a continuity check is a waste of time as the electronics in the pump means you don't get any sensible resistance readings. Indeed in one direction it is infinite. I guess the pump has an internal blocking diode to stop damage if wired the wrong way round.
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