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krasuskyp krasuskyp is offline
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Join Date: Nov 2001
Location: top of 3rd
Posts: 4,141
intermittent misfire - diag help please?

My '87s back on the road after sitting since 11/1 (schwing!). It gotten periodic drives during the sabbatical.

I've been commuting in it last week, and now I'm getting an intermittent misfire. Stock, save for Brian's exhaust/round air filter/removed decel valve & O2 pump.

The misfire is only under boost - some days does it w/o fail, some days it runs perfect. Ran fine whole way in this morning, then misfire developed when I got off the exit ramp. WTF? Clutch in and rev and it revs free.

My plugs/cap/rotor/wires are MAYBE 10-15k old (if that) - I'd think they'd be good still?

I do have one of the 2 vacuum advance line on dist that is crusty, the one that runs up to some solenoid looking thing (pardon my ignoramus) under the LF of the intercooler. Hoping it's that maybe?

Do our cars have the ability to derive codes (blink them?) from the CIS control box? Does my distributor have a hall sender? Buddy of mine who's helping me thru the thought process posed these Q's.

I don't get tho how / why it is so intermittent. Ran fine thru monsoonal rainstorm, clear cool and dry this a.m. and misfire. Doesn't seem to be a hot / cold issue either. Soon as boost builds - misfire - regardless of gear or rev... entirely boost related. Lift slightly and it's gone.

Also, unrelated - or maybe related?

I failed emissions last week (no cat / Brian's exhaust)... 1/2'd the hydrocarbons and the NOx readings (schweet!), but doubled the CO2. I tried turning the CO adj screw atop the metering plate to ZERO EFFECT - WTF? I turned it all the way out to where it was near falling out - didn't change a thing w/ the reading or the way the car ran. Turned down all the way near tight and same thing. This screw worked last summer when I'd last dialed it in. It's the one on the far left top of the metering plate, spring loaded - yes? (sorry, I'm dumb)

I 'thought' I'd turned it back to where we began, and the car runs fabulous otherwise 8-/. Plus the misfire was there (or not!) the week prior.

Any insight greatly appreciated - TIA gentz...
Paul... CT | '87 930 | '07 //S6 v10 JNR | '98 ///M3 vert |

| '01 ///M5 | '96 993 C2 cab | '05 S600 Sport - biturbo V12@Just Not Right 495rwhp / 612rwtq |
| '58 TR3A | '01 //S8 | '95 //S6 6gang | '88 ///M5 | '87 190E 2.3-16 |
Old 07-27-2010, 05:45 AM
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