EFI trouble shooting.

[Ed]

just thought id post a tale about some EFI trouble shooting....

The motor was idling unhappily, misfiring and generally rough.... not so good for an EFI equipped motor.  I thought a lead must've jumped off but a quick roadside check revealed all leads OK. hmmm had better nurse it home.

Unexpectedly every neighbourhood hoon was up for a traffic light race, from the guy in a SSS pulsar to an angry bloke in his Hyundai...  even more unexpectedly the old wagon didnt lose an inch to the SSS and effortlessly moved in front of the Hyundai to get into the right turn lane... not bad for 7 cylinders of vibrating mass.

Anyway after that bit of fun the old girl was sounding worse and worse.

Back in the garage the next day, whipped off the dizzy cap and found all OK, cleaned the contacts and rotor button...

Started her up and still misfiring.  By dabbing the exhust with a wet finger, i found no 4 was not firing.. handy hi tech diagnosis tool...

Checked spark on 4 and there was good strong spark on all cylinders... incidentally i also found that AC delco plugs seem to produce a fatter spark than NGK.  While not quantifiable I repeated the expierment over and over with consistent results using same brand but different plugs.

Whipped out the no 4 plug and it was dry (no fuel!) and no 2, 6 and 8 were sooted up... funny as no rich codes were flashing up on the Check Engine Light.

Checked compression just to be sure and there was 125psi cold on no 4.

So...discovered one of the leads into the injector plug to no 4 had come away slightly so there was no pettrol being injected and it was pumping air.  Luckily for me the Delco 808 is a "batch" injection where all injector fire each cycle.. so a simple test using a test light revealed the circuits were not short or open.

The O2 sensor is mounted in the exhaust manifold of that bank and was telling the injectors to widen the pulse width to compensate for the perceived "lean" condition.  This was the cause of the sooty plugs and poor driveability.

Took it out for a test run and for the first time since getting it on the road feel happy with its driveability.

it's a shame i'm away for work again this weeknd as i want to cruise it!

Cheers

Ed

[craiga]

Good post Ed, very interesting.

The fuel injection system operates in a closed loop, so one symptom (like the misfire) could be caused by one of a multiple of reasons within the closed loop OR in the other external systems (such as the secondary ignition system).

Does your system have a method to allow it to be put into an open loop condition? I've also seen that, since the introduction of the OBDII standard, that scan tools have greatly reduced in price. When I left this industry in '98 this standard was just arriving and seems to now have made it so much easier to interrogate and fault find ECU based systems. Previously we used to sell  a scan tool and then a HUGE box of interface cables to suit various vehicles.

I like the wet finger method, very useful. How do you test for spark though - hopefully not with your tongue 

Cheers,

Craig.

[Ed]

Hi Craig,

I can dagnose the system running in open or closed loop however i would proabably need to induce a set condition to force it to run open.

particular combinations through the ALDL usually enables this but I woiuld need to do some reading to check.

the other hi tech tool i use to get the codes out from the ECU and diagnose faults is a paperclip.

im contemplating getting Kalmaker so I can re-map my chip whenever I change any engine parameters.

who said EFI was difficult?  It's a load of fun.

Cheers

Ed