Mi16 Hesitation Under Load.

[davemar 16]

I've just installed the Motronic ML4.1 loom on my 205 Mi16, after quite a few teething problems. I finally got round to taking her for a test drive and it wasn't perfect. Under gentle throttle it runs fine, the idle seems good and revs cleanly when not under load (i.e. stationary in neutral). However when I try accelerating hard it is very hesitant between 3k and 5k rpm, and I think it is more likely to be ignition related as the rev counter looked a little shaky (though it is difficult to tell).

 

It does it all the time, so I don't suspect a loose connection. The coil is new, as are the HT leads, dizzy cap and rotor arm. The ignition amp is new too, but is an Intermotor one (is this likely to be a problem?). The AFM seems to give a smooth resistance reading when I move the flap, so I think that's OK.

[Tom Fenton 1,541]

Once it pops s*its and farts it's way up past 5k rpm does it then rev cleanly to the limiter?

If so I've had the exact same problem a number of years ago on a 405 Mi16x4 I bought with a running issue, it was the (brand new looking) ignition amp.

[davemar 16]

Past 5k it does seem fine, so the amp does appear to be the main suspect. I've got a spare one which I'll try tomorrow if possible.

 

It seems these ignition amplifiers are a constant source of trouble and getting hold of the good ones seems to be quite hard. I'm tempted to look at making an amp out of discrete components that does the job.

[numbum 0]

Yeah i've had the exact same problem 4.1 motronic i've been through more amps and looted a million scrapyard's as mine devolped a miss over night that i could not get rid off.

But some amps wouldn't even run it even a brand bosch one i purchased didn't solve anything apparently they changed the design nice 1 bosch so like i said i was stuck for months i tryed coils plugs checked all my wiring etc.

It ruined my day's and nigths the misses damn near kicked me out until i had a light bulb mo !!! and changed the coil for the original can type gti 1 and it was cured i found it something to do with primary and secondery resistances as this tipped me over the egde for so long i hope this helps never had a miss since woo hoo !

[davemar 16]

So the old style can-type coil worked for you? I've still got one of those so I might give that a go. Bit of PITA as I'll have to change the coil connector though, but worth a try.

[numbum 0]

Yeah i know its a pain swapping the connectors but the only way i found this problem was during my various head scrachtings i put an snap off inline spark tester on the ht to watch what was happening,

but then i found it missed less with this tester in the circuit as i was making the spark stronger by jumping a big air gap ie the tester,

so just by chance i flicked through an old autodata and was looking at coils etc and this is were i found about the resistances.

 

But a lot of probs are the amps but this was mine so if you get no look with swapping the amps it might be worth a shot like i said it ruined last summer for me but now its top notch .

[davemar 16]

I just tried the old-school barrel style coil and that was no better, still the mid-range hesitation.

 

I've ordered some ISL9V5036P3 IGBTs to try and build my own ignition amp, as I've lost faith in these modules.