Need help deadspot/misfire!!!

[mzollo]

alright guys so my 87 325i is acting. first it was a slight stalling dead across all 6, replaced the CPS and it seemed to go away. i tested the car only for an afternoon because i had to go back to school. came home two weeks later same problem. replaced said parts below all seemed to make it run better. now it has a what id like to describe as a dead "zone" from 3k-3500RPM, now it is not* very consistent and seems* to be only under load. car still has plenty of power and runs great except when it misses. its like the cars dies completely for a split second and then its alive. causes a jerking motion when it happens. ive been trying to figure this out for a long time but first here is a little history on my car

87 325e
swapped to 173dme and now a 2.7 stroker. just a heads up to give you guys some kind of idea.
new plugs
new CPS
new AFM

same old problem. can someone shed some light??

[ethirtydavid]

I had this exact issue in my first e30 and it was fixed with the replacement of my coil.

Also, I have seen this happen as an issue of crank position sensor wires grounding out due to bad routing there near the fan / waterpump pully. < This case was much trickier to track down.

[FLG]

OEM CPS sensor?? Ive had aftermarket sensors cause the car to run like complete crap, even ohm'd out of spec right out of the box

Also check the AFM resistance bar, could be worn out in that spot.

Also had a similar issue at 3k, random really...would just die and catch itself.

When the issue happens keep an eye on your tach, does it cut out completely or does it continue to read engine rpm properly? If it cuts out your looking at a CPS/Wiring/possibly DME issue.

[mzollo]

my coil seems to be within spec, and the CPS came off a known working model, well the only thing thing that i notice on the dash is the econogauge goes all the way to 0 then back to 40(its not hooked up) different wiring harnesses i guess.

[FLG]

Economy gauge doing that could point to a dme that is loosing power momentarily. Double check continuity beteeen the battery and the fusible link on the smaller wire that runs in the trunk (fusible link is about a foot into the small wire going to the battery) . Also had an issue where the fusible link was split but in a way that it would work most of the time.

Also I had a setup of lights, dme needs main power and switched power (when you turn the key) forgot which pins they are but a quick Google search will give you answers. Use quick splices on those 2 wires and hook up small led's and look to see if either light goes out when the event occurs.

Finally in the end, it all turned out to be the connector on the firewall that is near the fuse box...wasnt even corroded but one day i just took it apart and cleaned it out for the hell of it...never had an issue again.



Sent from my Galaxy Nexus using Tapatalk 2

[jlevie]

my coil seems to be within spec, and the CPS came off a known working model, well the only thing thing that i notice on the dash is the econogauge goes all the way to 0 then back to 40(its not hooked up) different wiring harnesses i guess.

Does the tachometer react when an event occurs? If it does, the DME is loosing power or timing data from the CPS. A bad main relay, bad fusible link, bad DME ground, or a flaky DME START input are possibilities. As is the CPS or wiring harness. If just the econometer reacts there is a problem with control of the injectors or with fuel system. Check C191 (under the intake) for corrosion. You can check for a fuel system problem by tee'ing a gauge into the supply line for the fuel rail and zip tying it to a windshield wiper so you can see what the pressure is during an event.

[mzollo]

not really sure if the tach reacts. its very wonky at best, it was never wired well. but i can replace the CPS and throw in a known DME, see if that helps i guess

[mzollo]

took it for another ride, the miss is not consistent. its at any RPM it seems and the tach stays with it when it does miss though