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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...
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Paul... CT | '87 930 | '07 //S6 v10 JNR | '98 ///M3 vert |
past:

| '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, 04:45 AM
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beancounter
 
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No codes available from the CIS box paul...the dizzy does have a magnetic pickup and the famous green signal wire comes out the side of the dizzy body into the harness. This wire provides the signal to the CDI box which lives next to the fuse panel on the driver's side on the engine compartment. These are known to fail (insulation cracks open from years of heat cycling) and cause weird intermittent misfires.

The fact that you say it happens only on boost would worry me...lean misfire? The car has sat a lot for over 6 months...maybe an injector is gummed up. Try running some seafoam or techron?

The mixture adjustment screw can be a bear to engage...are you sure you were actually turning the adjuster? You have to press down on the spring loaded plunger pretty hard and its tricky to get it to properly connect to that adjuster screw somewhere in the bowels of the CIS airflow meter housing. Once its engaged, only slight turns will change the idle speed of the engine.
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Old 07-27-2010, 05:27 AM
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Also check the over boost sensor switch. You'll find it on the back side of the bypass valve assembly, towards the drivers side. There is a single wire connected to this (the color of the wire is usually white). The overboost sensor wire must be grounded in order for the fuel pumps to run. When the the switch senses too much boost, it cuts the ground, and fuel pumps stop. You could rule out the switch by temporarily grounding the wire directly to the engine...take the car for a drive and see if you still have the problem.

In your car the switch works with a rectangular yellow relay in the engine compartment electrical panel that is famous for causing trouble.
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Old 07-27-2010, 05:33 AM
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Thanks for those pointers Jacob, will run some techron today and check those wires tonight.

I thought I was turning the CO screw but clearly I wasn't 8-/. Will try again, I've got 60days to re-test...

LOL... yours / my post count is identical today 8-)

Please keep any other thoughts coming - much appreciated.
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| '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, 06:00 AM
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Paul as Jacob stated you probably didnt have the co adjustment fully engaged, however, when you go and try to lean it out for you emissions left lean right rich and do not go and make huge turns small adjustments are all that is needed. hope to see you again at the fall palooza and yes attendance is required and dont forget the billy bob teeth
Old 07-27-2010, 06:31 AM
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I would be tempted to try a set of fresh plugs, maybe 1 range hotter. Also, gas that sits for awhile can often times become problematic.

79 930
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Old 07-27-2010, 08:09 AM
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Whatever you do .... if you are going to work on your engine ... it is mandatory that all work be done at a highway rest stop ......

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Old 07-27-2010, 08:26 AM
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2 new tanks 'o gas thus far

f'n A - go out for lunch... no miss!

get off highway... miss!

park for lunch w/ lid open, let cool 25min maybe... miss still there.

get on highway... miss begone!

I sodonot get it.

Heh, Paul - 1st... those are my tools Petey's wielding even! 2nd - BTDT d'oh!:

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Paul... CT | '87 930 | '07 //S6 v10 JNR | '98 ///M3 vert |
past:

| '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, 10:13 AM
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misfire under load

Hello Paul;
Good ideas from the other guys. I'm thinking a fuel issue here. Misfire is mostly under load could be a restricted fuel filter or a fuel pump going bye-bye. When it starts to die, it'll fail intermittently under load. As it gets worse and pressure drops, the misfire will become more consistent. Our 930s are thirsty under load and we need lottsa pressure and volume; perfect pumps are critical.

I think that you failed CO emissions due to an improper CIS mixture (adjust the screw properly). Let us know.
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Old 07-27-2010, 11:31 AM
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Tx Paul - hugely cool of you as usual! I'll def let you know. My coldstarts are immediate, it's my hotstarts that suck arse! (cough accumulator cough!)...

now

I'm not even going to admit (nope!) WTF I did wrong w/ the CO screw - I was in my work clothes in a dark emissions bay is all I'm saying - d'oh! 8-) I'll pass 'this time' heh heh...
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past:

| '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, 11:59 AM
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Check your plugs carefully.... similar situation... New plugs fixed it!

GL.

Walt
Old 07-27-2010, 12:10 PM
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Check/replace plugs first...one or more might be misfiring only when under load.

The recurring thread here, if I'm reading all the facts correctly, is that the misfire (when it happens) is always under boost conditions, whereas light load (i.e., no appreciably boost) she runs fine. Which leads to one other possibility - that you have a dried out or dislodged seal or two on the IC and/or turbo pipe plumbing. Under boost is when you would notice that the most, as you would be leaking out the already metered air before the throttle body and end up with the pig-richies to where she sputters and generally runs like $hit 'cause your AFR's have dropped off the scale. With a minor seal or o'ring leak it may not open up enough until you start cramming boost air in there.
Isn't CIS fun?
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Old 07-27-2010, 01:21 PM
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Tx Walt / Mark.

Jacob called me and re-reminded me that despite "what you know" - start w/ the basics. Despite thinking my cap/rotor were ~ 10-15k old, I pulled them and found them looking somewhat scuzzy. Contacts not scored deeply but very black. Scuffed them up and reinstalled, checked all vacuum lines which despite looking dry didn't show any cracks. The rotor contact was near-flush with the orange rotor, nearly no 'protrusion' which somewhat surprised me.

Ran fine this morning - fingers crossed!

Thanks for the support guys!

Pulled a plug for giggles (only 1, ran out of time), looks good to me but what are your thoughts?



also

WTF is this brown wire I found loose? It's coming out of the loom of all the other brown wires, there is a clone to it but a shade darker that is attached to the red rubber thingy (I think that's the boost signal for the gauge?), but was just dangling there tucked away.

AND

what is the stubby rubber hose coming off of the back of the 'solenoid' that my pinky is holding? It's not connected to anything - is it supposed to be? (ignore my temp ghettofab tape job of the other wires)



Any insight appreciated!

For shiggles, I re-connected my decel valve while I was in there. FAWKING-A... I'm jonesin for a long flathead here @ my desk now - I'm near embarrassed to be subjected to the ride home in such unacceptable silence!!! Gotta have that snapcracklePOP! 8-)
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Paul... CT | '87 930 | '07 //S6 v10 JNR | '98 ///M3 vert |
past:

| '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 07-28-2010, 05:15 AM
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Paul,
That looks suspiciously like the over-boost sensor wire.. If it was off the car wouldn't start.. It shouldn't go to the air solenoids however..
To me your plugs are looking pretty rich.. but I'll defer to the others in the brain trust.
if you're running that rich, it could easily cause misfire under boost
Clean up the plugs, get your mixture right and see where you are at
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Old 07-28-2010, 05:32 AM
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Quote:
Originally Posted by 9dreizig View Post
Paul,
That looks suspiciously like the over-boost sensor wire.. If it was off the car wouldn't start.. It shouldn't go to the air solenoids however..
To me your plugs are looking pretty rich.. but I'll defer to the others in the brain trust.
if you're running that rich, it could easily cause misfire under boost
Clean up the plugs, get your mixture right and see where you are at
Yepper, that's a big 10/4. Hook that baby back up to the OB sensor or at least ground it out. Otherwise, your fuel pumps won't run at all.

Maybe it was hanging on by a thread, sometimes failing contact.
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Old 07-28-2010, 07:38 AM
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lol guys - I drove it in this a.m. w/ that wire still dangling there 8-)

Dunno what goofiness might exist w/ my car's wiring. All I know is the PO's shop (same one I sometimes use) did convert the wiring (fuel pump relay/wiring stuff IIRC) over to "Euro-spec".

I do know the OB sensor works fersure tho, when I got the car years ago the WG was frozen and the OB would shut her down @ 1.2bar.

Guess maybe it's "otherwise" wired for some reason. Where's the OB sensor again?

And, how about that short stubby black hose on that solenoid - is it supposed to run 'nowhere', open to atmosphere?

It's hard as I've take a ton of crap off my car - A/C, air pump, etc. and I forget what used to go to what 8-/.

Tx again guys, keep the thougths coming pls!
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Paul... CT | '87 930 | '07 //S6 v10 JNR | '98 ///M3 vert |
past:

| '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 07-28-2010, 07:52 AM
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GREAT!!!!!!!!!!!!!

I currently using densos with good success $2.00 plug. w24esr-u. Already pre-gapped .032.

Personally, I would use MMO with your next fill-up to clean up some of that carbon.
My car runs like a charm.

or NGK racing plugs r5671a-8-- I think Mark uses those with success.

Walt
Old 07-28-2010, 10:42 AM
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Quote:
Originally Posted by krasuskyp View Post
lol guys - I drove it in this a.m. w/ that wire still dangling there 8-)

I do know the OB sensor works fersure tho, when I got the car years ago the WG was frozen and the OB would shut her down @ 1.2bar.

Guess maybe it's "otherwise" wired for some reason. Where's the OB sensor again?

And, how about that short stubby black hose on that solenoid - is it supposed to run 'nowhere', open to atmosphere?
Paul, your car is driving me bannanas! Mystery wiring jobs...uuggghhh!

So, she runs without the OB sensor wire attached. That's interesting, someone bypassed/rewired the protection circuit. Without that wire connected to the OB sensor, then how can the sensor sense overboost conditions and shut her down at 1.2 (or any) bar? The sensor is a normally closed switch that connects the wire to ground...which keeps the pumps running. Overboost opens the switch and interrupts the ground and shuts down the pumps.

The OB sensor is sitting on the secondary intake manifold (boost recirculation manifold) top-left near the back side of the recirculation piston housing, if I recall. Mine's all hacked up so I'm going by memory here.

That short stubby black hose on the solenoid is just a vent to atmosphere.
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Old 07-28-2010, 10:51 AM
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Tx Walt - will have a look @ those.

Todd... I had an epiphany @ lunch: if I'm not mistaken (entirely possible/likely), my GReddy Profec B Spec II boost controller is hooked up to the OB switch - straight behind my hand in the pic above? So they prolly installed that and flopped the orig brown wire there. Yes?

FRANK! D'oh sorry broham forgot to reply to you - na mon on NC in Oct, flying do Disney AGAIN (argh!) and it's over my anniversary so I'm a 2time loser.

Plus, I've already cashed in _entirely_ too many chips for car fun this year - flew down to Zuff for magazine recon in Feb for Justin's heap (*should* be in next mo's issue???), was out in Denver for an Audi gig for the mag, got //SFest coming up - wish there was a way, trust me.

I'll be there in spirit, funny teeth and all... you should have seen me trying to get my license renewed w/ those on - now there's a story for ya 8-). Hope yer well me friend!
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Paul... CT | '87 930 | '07 //S6 v10 JNR | '98 ///M3 vert |
past:

| '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 07-28-2010, 10:56 AM
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"Paul, your car is driving me bannanas! Mystery wiring jobs...uuggghhh!

So, she runs without the OB sensor wire attached. That's interesting, someone bypassed/rewired the protection circuit. Without that wire connected to the OB sensor, then how can the sensor sense overboost conditions and shut her down at 1.2 (or any) bar? The sensor is a normally closed switch that connects the wire to ground...which keeps the pumps running. Overboost opens the switch and interrupts the ground and shuts down the pumps."

This can be done by simply grounding the white wire from the overboost sensor next to the speed relay under the driver seat.
Maybe someone got sick of the overboost circut or didn't want to buy a new sensor and did that in the past.

The yellow relay is not the overboost relay like everyone thinks, the "speed relay" under the driver seat has two internal relays on it's board and handles more than one function.
This "speed relay" farthest to the left under the driver seat disconnects the 2 red fuel pump relay grounds when the overboost sensor disconnects the white wire from ground. It also disconnects the red fuel pump relay grounds if rpms go somewhere around 7000-7200 rpm so it is also the factory rev limiter.
Old 07-28-2010, 11:41 AM
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