another 3.2 misfire question - solved
 

SmileWavy

UPDATE - dosed it with Techron - ran the car 100 miles today (4-12) - using same DME as when problem originally surfaced

- no more misfire - fingers crossed

maybe just a sticky injector

it's been a year since i got my 3.2 conversion running, much thanks to many related threads here - and it was quite delightfull once the initial issues were solved

now i have a new misfire problem that recently surfaced :confused:

- it did not do this for the first 1500 miles or so - it would previously pull like a train in 5th from 1500 rpm with gentle throttle input and never required shiftdown even on relatively steep grades- it was like having an automatic trans

now the thing "bucks" or misfires under low-rpm load in higher gears at mid-to-deep throttle - e.g. under 2200, 4th-5th, especially pulling up an incline - if i downshift it is OK

and it occasionally "hiccups" on an uphilll pull even in lower gears at higher rpm (i.e. 3000) - almost as if there is a momentary total electrical disconnect, like maybe a loose connector somewhere - but i've checked all the connections & found no problems

fwiw - it recently got a new cap, rotor & plugs after getting very wet during an August deluge and developing a really bad misfire (http://forums.pelicanparts.com/porsche-911-technical-forum/714211-misfire-after-storm.html), - it ran perfectly after that fix

until now - as described above

the still-oem wires & plug ends test OK per spec & show no cracks or nightime arcing

- i have 4 good DME's and have swapped one just to rule that out; also has new pump & filter, etc

and yes i have the Test Plan and have been thru all that stuff (search my other 3.2 posts)

here is a relevant thread:
http://forums.pelicanparts.com/porsche-911-technical-forum/719543-3-2-engine-jerking.html

?? any good ideas that are speciific to such a misfire?? :confused:

? has it actually happened to you & what solved it?

TIA

Is the bucking occurring under low RPMs and slow acceleration? What kind of chip do you have in her?

yes - low RPMs and slow acceleration, as i tried to described above

stock DME '89 - also have tried different rebuilt and chipped DME - no differences

the "hiccup" described is a different issue but maybe related ?

.this is just an annoyance right now that tells me something is not quite right, but ya never know when some intermittent symptom is a precursor of a sudden worse problem that will happen at a most inopportune time, like halfway to Parade in Monterey (entrant #744)

.

Not for Nothing, but how is the Dizzy, remove cap and see if there is any slop on the rotor, up and down and or axial. I had miss fires when my dizzy's internal bearing wore out.

If I may suggest try not to put other DME's into your car, if the fault is your car, it will damage the DME. Which performance chip was it?

Low rpms bucking is usually the characteristics of an OEM chip

or, a long shot

Have you replaced the fuel filter?

I am sometimes in the area, if you like I can swing by and test your DME in my car.

PM me,

Jim

How old are the flywheel sensors?
Check the AFM for any flat spots (9V battery, DVM, then move flapper through entire range)

Check for vacuum leaks. Spray some carb cleaner around the rubber sleeve that connects the two intake manifold halves and see what happens. Mine was bad and caused some low rpm bucking and also higher rpm missing. These rubber seals swell with age and leak.