need urgent help. serious miss fire

zetecmk2 · Post by **zetecmk2** » Wed Oct 27, 2010 8:57 pm

running a MJLJ map type on my zetec.

when running the engine without the MJ connected the engine runs fine in limp mode. as soon as i connect the MJ it starts to miss fire badly and will not run properly.

it was all working fine until one day it just started miss firing out of th blue.

checked all the connections and wires. there all fine.

chaned the plugs, coil, CPS, leads are 3 weeks old. really need to sort it quick

thanks

cng1 · Post by **cng1** » Wed Oct 27, 2010 9:40 pm

If you are running with TPS then check the calibration of that.

zetecmk2 · Post by **zetecmk2** » Thu Oct 28, 2010 5:27 am

its a map type. i brought it from trigger wheels.

it ran perfect up until a couple of days ago..

cng1 · Post by **cng1** » Thu Oct 28, 2010 7:02 am

If you connect up the computer does the map on the ECU look correct and that the load(MAP) values look correct. You should expect the MAP values to be approx 100 with the ignition on but engine stopped and 30-40 when idling.

Post by **brentp** » Thu Oct 28, 2010 4:13 pm

Agree, first step is to monitor the software to see what the 'real time' readout is indicating. The RPM reading should be consistent without any jumps or glitches.

Also would be good to put a timing light on the engine to verify ignition timing stability.

zetecmk2 · Post by **zetecmk2** » Thu Oct 28, 2010 5:42 pm

i had the car ticking over and a strobe on each lead in turn, and eeach lead had a mis fire.

i'll check the software in a bit and report back.

thanks for the help.

zetecmk2 · Post by **zetecmk2** » Thu Oct 28, 2010 6:41 pm

ok

just ran the car with it at 2k. the runtime graph is all over the place.

the map sensort reading stays pretty constant, but the rev and ignition advance jump about all over the place. but the rev counter on my clocks in the car stay quite still.

stuck for ideas now,

thanks chris

cng1 · Post by **cng1** » Thu Oct 28, 2010 7:51 pm

So the MAP reading is definitely varying between 100 engine off and 30-40 kpa stationary, if so then that is good.

If the RPM is jumping on the software but not on the rev counter on the dashboard then the obvious question is where does the tacho get its feed from - is it the megajolt, the EDIS module or via the coil pack and a tacho adaptor? The reason for asking is that if it isn't jumping around it suggests that either there is a lot of damping on the needle or that it is taking a different (and more reliable) feed than the ECU. If it is taking the RPM feed from somewhere other than the megajolt itself then I would check the PIP and SAW wiring as there may be a communications problem between the EDIS module and the ECU

zetecmk2 · Post by **zetecmk2** » Thu Oct 28, 2010 8:25 pm

The rev counter on the car is wired from the megajolt.

Yeah the map sensor did as you describe.
I have checked the PIP/SW wire and can't see any damage, but I'll check again.

Thank you for the help
Chris

cng1 · Post by **cng1** » Thu Oct 28, 2010 8:46 pm

OK. You said that the revs and ignition is jumping all over the place. At an idle how much is the indicated revs fluctuating by and does your Mk1 ear agree with the stationary rev counter or the computer display?

I'm guessing that the timing jumping around is just as a result of the revs bouncing between two load sites, each with very different timing values in them. Sometimes something as simple as a slight change in throttle stop can cause the engine to try and idle at a very slightly different point to normal with the result that it pushes it from being clearly in one load site to just between two, if those two differ substantially the engine can surge back and forwards between the two.

zetecmk2 · Post by **zetecmk2** » Fri Oct 29, 2010 12:42 pm

right....

the rev on the megajolt software is jumping from around 1k up to 4k in surges, which like you sya is causing the timing jump around.

i agree with the rev counter on the car.

i dont know how to solve it though. i have deleted the map on the MJ and re put on the map. made no difference.

thanks for the help

chris

cng1 · Post by **cng1** » Fri Oct 29, 2010 1:35 pm

That is a bizarre one. You're not routing the PIP wire anywhere near anything that could be causing interference could you - near the HT leads/next to the alternator or anything like that?

On the zetec you should already be running resistive spark plugs (usually identified by an R in the part number) but if you've changed them for non-resistive versions then I would change them back again

zetecmk2 · Post by **zetecmk2** » Fri Oct 29, 2010 5:39 pm

bizarre isnt the word!

PIP/SAW wire runs along the bulk head. nowhere near anything other than the brake servo.

the engine ran fine on the old plugs then started to miss, so i changed them for the excat same ones. and it made no difference...

out of options now.

cng1 · Post by **cng1** » Fri Oct 29, 2010 5:57 pm

For the rev counter to be stable and the revs in the software not is most bizarre when the rev counter is fed directly from the megajolt itself. I can only imagine that the rev counter is damping the signal so much that the spikes are averaging out.

If it weren't for the rev counter readings I would say that you were getting some false triggering but on the zetec with the factory flywheel based trigger pattern and crank sensor but that is ruled out since you're not getting the misses in limp-home mode. OK, how about this as a diagnostic test - disconnect SAW but leave PIP plugged in. That will effectively leave you running in limp-home but the megajolt should still see the RPM. The results should be interesting although not delivering of an immediate fix.

Spockie-Tech · Post by **Spockie-Tech** » Fri Oct 29, 2010 10:40 pm

Have you checked that the spacing between your VR sensor and your wheel hasnt changed and that your mounting bracket is solid ?

I'm guessing that CPS = Crank Position (VR) Sensor ? So you swapped it for another one ?

You say you have checked the wires and they're ok..
How have you checked them ? Just Visually or have you given then a check with a meter and a good yank to make sure they are connected solidly ?

We were doing some MJ testing on a Dyno a month or so ago... Worked fine for a day or two, then developed a weird mid-rpm misfire that we couldnt find after a few hours of fiddling about, so we had to pull the engine off the dyno.

Later on, going over the wiring, I found the soldering on a terminal leading to one of coil pack wires had broken, but the heatshrink was still holding the wire in contact with the terminal.. mostly.. Once the heatshrink was cut off, the wire just fell off.

I suspect that at mid-rpm, the vibrations would have caused that coil pack to spark weakly or at the wrong time.

So give all of your wires a good twist and pull at the connection points, and double check with a meter while doing so if you still cant find anything. Chances are good that the problem is a bad join somewhere if the install had been working for a while then developed a problem like you describe.

If that doesnt work, find someone with a 'Scope who knows how to use it and start looking at the VR, coilpack and pip/saw waveforms.