Cold Start Misfire Diagnosis

Fox588 · February 15, 2013

Hi everyone, I don't have a lot of 7.3L diag under my belt, I have a 2000 F-350 with a cold start misfire that last time it was in also idled rough when warm and the cylinder contribution test showed cylinders 3,7 and 8 low IIRC. replaced those injectors and it ran better. now it's back with just a cold start misfire for the first 30-40 seconds. meanwhile the IDS won't allow a contribution test with EOT under 170 degrees.. is there a simple way to fool the EOT reading or should I be taking a different route?

if only we had power balance for these..

Alex Bruene · February 15, 2013

The audible buzz test works well to identify weak injectors when they're cold. Run a buzz test, and listen for the weak injectors. You can also use a short-out box (if you have one)... Or hook your gage tester up to the EOT wiring and dial up the resistance to simulate the warm engine.

Bruce Amacker · February 15, 2013

What are Perdels?

Read this page about halfway down:

http://www.forddoctorsdts.com/forums/ubb...=true#Post22830

A compression test is always a smart idea as 7.3's are getting tired.

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Brad Clayton · February 15, 2013

Not trying to pull you in every different direction, but I had one doing something similar yesterday and it ended up being the wiring harness where it attaches to the engine at the left valve cover. The wiring had rubbed on the valve cover exposing some copper on a few wires.

Keith Browning · February 17, 2013

,,,the wiring harness where it attaches to the engine at the left valve cover. The wiring had rubbed on the valve cover exposing some copper on a few wires.

That is an oldie but a goodie and I still inspect for that to this day when I have a 7.3L in for a driveability concern which is not very often anymore.

Fox588 · February 21, 2013

Thanks for the quick tips, I've been trying to learn this stuff the hard way.

I had no idea what PERDEL's where, but didn't have any luck getting them to work on a 01' with a lope at idle today, EOT was above 170.. it had an EBP circuit fault though. Couldn't really commit any time to it though as the customer only wanted to have his PCM flashed to stock.

We have quite a few 7.3's coming in for some reason, most of them are over 250K miles

Being originally from NH I didn't see many of them in at the dealership, down here in

FL there seems to be plenty of company fleet trucks still in service.

Brad Clayton · February 21, 2013

I feel your pain there brother. Living in Vermont, I haven't worked on 7.3 in about 4 years. Moved to NC and I have never seen so many 7.3's still on the road in my life. Worked on quite a few recently and had to dust off my memory banks.