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cycling misfire[200/85] posted by Jason Goodley on
Sunday, 8 November 1998, at 2:00 a.m.
I have been trying to dianose and fix a misfire on my 85 244 DL. The miss has a definite cycle to it, the engine will miss then run smooth for a few seconds and miss again(the interval is always the same). At higher rpms the cycle is the same but the interval between the miss is shorter. And with the idle adjustment screw all the way in the idle speed will only go as low as 900 rpm.
HERE IS WHAT WAS REPLACED/DONE
Idle air motor
spark plugs
cracked vaccume lines
spark plug wires
injector seals
cap and rotor
throttle body was cleaned
throttle plate reset
What could cause this mysterious misfire??
Re: cycling misfire[200/85] posted by Don Foster on
Sunday, 8 November 1998, at 8:44 a.m.
Jason --
Forgive me, but is this like calling the doctor and saying, "Doc, I gotta headache. What's wrong?"
Sorry -- but that felt good! Anyway, maybe your headache is caused by:
- An intermittent injector
- A bad injector ground on the intake manifold
- An intermittent wiring harness ('85's one of the affected years)
- A bad connection at the injector at the injector
- A defective FI ecu (let's hope not)A bad injector O-ring seal
- A dirty injector (have you run some cleaner through?)
Then I'd try to determine which cylinder was failing. One method is to start the engine cold, and if it is misfiring, turn it off after 15-30 seconds. Feel the four exhaust headers to see which is coolest -- that's the miscreant.
If it won't misbehave when cold, then later, as it's skipping at idle, unplug the injector connectors -- one at a time, in sequence. The cylinder that has the least drop in RPM is the problem.
All four injectors are wired in parallel and receive the same pulsed (grounding) signal from the ecu. You can interchange the injector plugs between 2 and 3, or 1 and 2, etc., to see if the misfire follows the injector plugs (could be a bad engine harness or bad ground connection).)
--Sunday, 8 November 1998, at 8:08 p.m.
another item to put on the list of things likely not checked is a broken valve spring.
Re: cycling misfire[200/85] posted by Don Willson on
Sunday, 8 November 1998, at 8:47 p.m.
Solder the injector ground wires to the crimps. After this many years they become a high resistance connector and can cause misfiring of the injector.
--Don Willson, '86 744, 115,000 miles, '89 765T, 135,000.