need urgent help. serious miss fire

cng1 · Post by **cng1** » Fri Oct 29, 2010 10:56 pm

It's a Zetec - the crank sensor will be mounted directly into the block just as it left the factory and the trigger wheel will be built into the flywheel. Wiring between crank sensor and edis module is an outside possibility as although the engine runs fine with the ECU disconnected that may simply be because the module when running alone will continue to fire for a moment after losing sync. With limp-home that means you just stick at your fixed 10 degrees of advance irrespective of what the state of sync is, with the ECU connected the PIP signal coming and going would cause the perceived RPM to fluctuate, pushing the ECU between cells with radically differing timing values.

Which brings me on to another diagnostic test. Having thought about it I believe that the test I previously described (PIP connected SAW disconnected) is likely to yield the same quality of running as limp home but still exhibit the rapidly fluctuating RPM on the ECU readout. If that is the case then the next step is to fill all the load sites with 10 degrees of advance and reconnect SAW. The quality of running should be unchanged (ie still "better") but the RPM will still be jumping around. If so that proves that the problem is a sync issue, be that on the PIP wire or relating to the crank trigger

zetecmk2 · Post by **zetecmk2** » Sat Oct 30, 2010 9:01 am

ok

i'll give all the wires a good check, and change the load values to 10 everywhere if this makes no difference, you say it could be a sync problem, how can this be if the can runs 'ok' in limp mode??

absoultley nothing on the car had changed when i got this misfire in the beginning, i just cant understand whats happened.

chris

cng1 · Post by **cng1** » Sat Oct 30, 2010 9:13 am

If the EDIS module can't read the signal from the trigger wheel for a moment or two it will assume that nothing has changed and carry on firing - obviously if the signal doesn't return rapidly it has to stop firing but if it is just a transient glitch it will gloss over it. In limp home mode whether the signal is glitching or not you're getting a constant 10 degrees of advance. With the ECU connected it sees the glitches as fluctuations in RPM, which bouces you around the load sites. If those load sites are all similar you probably wouldn't notice much difference from the behaviour in limp-home but if some of those load sites are 10 degrees and others 40 degrees then the timing will be jumping all over the place and the engine will run rough as a result.

zetecmk2 · Post by **zetecmk2** » Sat Oct 30, 2010 9:32 am

so really the only logical explanation is a broken loose wire?? either on the CPS or the PIP/SAW signal cable?

cng1 · Post by **cng1** » Sat Oct 30, 2010 9:48 am

That does seem the most likely explanation

zetecmk2 · Post by **zetecmk2** » Sat Oct 30, 2010 10:13 am

ok

well i have just removed my complete install ready to start again making sure everything is connected and wired properly.

just have to hope i find the problem.

if its not a bad connections any ideas on what could cause this?