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lean miss-fire at cruise

the coil fixed the miss that i could actually feel while driving, but i still have the original miss fire while cruising. when i got the car, i found the cruise mixture to be in the 16's. idle and boost mixture was good. 13.5 and around 12 for boost(?).
runs good under boost and has good idle, its just in between that is the problem.
i some popping from the exhaust while cruising. i think i am noticing a trend that it is somewhat smooth as soon as i hit a steady speed, but the longer i stay at the same speed, it gets worse. may just be me, dont i dont know.

i have been through EVERYTHING.

no O2 sensor
no freq valve
euro FD- W/larger fuel lines
injectors- ?
054 WUR
header (B&B i think)
dual out exhaust
RUF intercooler
K27

compression- 120 left side 130 rt.
leakdown- 4%
fuel flow out of FD/no injectors- 3 at 5.3 oz's. low was 5.1 hi 5.6
fuel flow W/injectors- no weights yet but it looks better than previous
spray pattern- not checked
swapped ignition wires with old set with better resistance
cap- cleaned and swapped
rotor- not changed
coil- new MSD
plugs- new but copper NGK's (not as good as the platinums)
timing- 26 degrees
advance works
retard works
valves adjusted
WCP- was 3.6, now 3.4 (no gauges or LM right not. brother has them)

1 could i have too much vacuum advance at cruise? i see where the dist was worked on by PO?

2 the coil was bad. could the CD be bad causing this? i have a replacement capacitor for the bosch CD. should i jsut go ahead and swap it?

3 should i drop the control pressure some more?

4 rotor? maybe i will pull the rotor. not sure if i have an old one. maybe its cracked

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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 04-16-2013, 08:45 AM
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You've been pretty thorough checking everything out!

I would get your cruise AFR down to the low 14's as a start. 16 is way too lean. So yes, drop your warm control pressure a bit. If that doesn't clear it, then it sounds to be electrical.
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Old 04-16-2013, 10:26 AM
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what electrical?

too much advance?

CD unit? would a weak spark make rich, or lean? wouldnt a weak spark show up more under boost?
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 04-17-2013, 04:38 AM
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Sounds like you're using the bosch CD ignition with an MSD coil. MSD does not make a coil with the correct impedance for the stock CD or a permatune CD. It will start and run but it can and will cause problems with the stock CDI.

The only coils that have the correct impedence or primary wire resistance for the stock ignition box that will work right are the old oil filled black painted stel casing Bosch coil for your car, the new oil filled brazilian made clear anodized replacement coil (that is unreliable mounted upside down on the fan housing) and the permatune epoxy filled coil made for the permatune replacement CD.

Or get a new MSD ignition box and use it with your MSD coil. That's probably the best thing to do because you don't know if your bosch CDI is good or not.

You don't say you have an adjustable control pressure regulator. If you don't you need to have yours modified by Brian Leask so you can lower steady cruise control pressure to get a little richer mixture during warm steady cruise.

I have one and have it set at about 15:1 steady cruise AFR on the interstate and it runs perfect. 13.5:1 at idle and mid to upper 11's under boost.
Old 04-17-2013, 05:46 AM
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Good point on the MSD coil and stock CDI, Jim. I missed that. Regarding AFR's, I run at cruise around 14.4 and at idle around 13.8. All relative as to what your motor likes.

As to the original poster, be aware that AFR readings are dependent upon remaining un-consumed oxygen in the exhaust gas. If you have poor ignition for whatever reason, then your fuel/air mixture may not burn completely and will leave unconsumed oxygen behind. Your oxygen sensor component of your AFR gauge setup will detect that extra O2 and report back a lean condition. Might be why you're seeing 16's at cruise.

As to having too much advanced timing, don't worry you don't have that. I'm running 38 to 40, in that ballpark anyway, at 4000 no-load rpm's. I think Jim's sitting about the same as well.
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Old 04-17-2013, 07:21 AM
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this is how it ran when i bought it, a slight miss that i could hear. then it started to miss where i could feel the vibration through the car. the MSD put it back to the orginal miss.

would un-burned fuel show as lean or as rich? this is kind of like what came first, the chicken or the egg. is the lean mixture causing the miss-fire or is the miss-fire making the mixture read lean? i thought the miss-fire would make it read rich.

i may have to swallow my pride a second time on this one. first i never thought the coil would make it have a miss. i ahve seen them get hot and not work, then cool and work fine.
second, as an electronics tech that has worked all my life on radar that is nothing more than a 60kv 50amp ignition system, for a transmitter, i would never think the impedance of the coil would make a difference for something like a bosch CD unit.

let me check the rotor and the green wire from the dist first before someone sends me a WUR or coil.

i have been thinking about buying a BL WUR. i just dropped $1500 on the mercedes so i was putting it off.

i use to have a 100:1 oscope probe here at work but i have not seen it in years. i looked at the signal to the bosch coil with a 10:1 and i looked at the signal to the MSD. i think the MSD one had a higher voltage. i may go back and compare.

thanks for all the help. i think it is coming down to the coil again or maybe the CD. i really did not think about the effects of the miss on the mixture, just the there was around
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88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 04-17-2013, 08:58 AM
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One other thing you could look at, check that your distributar rotor is pointing where it should be when your #1 cyl is at TDC and the PO didn't put it in one tooth out.
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Old 04-17-2013, 11:59 AM
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Quote:
Originally Posted by JFairman View Post
I have one and have it set at about 15:1 steady cruise AFR on the interstate and it runs perfect. 13.5:1 at idle and mid to upper 11's under boost.
That's right where mine is, and I'm very happy with it. I've had my cruise close to 16 and would always get a slight miss every 10-seconds or so. At 15, I have a little room and it runs purr-fect... The other issue with being close to 16 was that if a cold front or high pressure system set in [in other words: nice take out the porsche weather], my car would all of a sudden run too lean. So, at 15, when those fronts come in, it might jump up to 15.3 at cruise [and no miss-es].
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Last edited by mooney265; 04-17-2013 at 02:14 PM..
Old 04-17-2013, 02:12 PM
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I like 15 at cruise because I feel like I might be getting a tiny bit more gas mileage.. or it may be only a few hundred more feet per gallon and a little lighter shade of grey in the tailpipe but it runs great and I'll take it
Old 04-17-2013, 03:20 PM
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i still have the spare Bosch CDI unit that you rebuilt for me that you can try, I may have a spare coil as well....

I drove with a Bosch CDI and MSD Coil for years with no problems, not saying it is / is not a good match, but my car ran fine. I did move back to the Bosch Coil though....
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Old 04-17-2013, 05:50 PM
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Quote:
Originally Posted by JFairman View Post
I like 15 at cruise because I feel like I might be getting a tiny bit more gas mileage.. or it may be only a few hundred more feet per gallon and a little lighter shade of grey in the tailpipe but it runs great and I'll take it
I suffer from that also.
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Old 04-17-2013, 05:55 PM
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Talking about a little gray...

13 at start - cold, 15 at idle, 15.5 at cruising, 10.5 ~ 11.5 boosting.
The car loves it!
Old 04-18-2013, 05:14 AM
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what control pressures are you at to get your mixture in the 14's? also, are you still running with the O2? i would like to be were timc is at,in the low 14's, but he is also running with his O2 and no header, if that makes a diference.

i though about that spare CD unit the other day. i also thought about trying your coil.


i still dont see the MSD coil being a problem, but i have been wrong about the coil already. although the coil makes sense because it seemed to run worse as the engine heated up.
now i think it is still somewhat related to heat, but perhpas due to fuel pressures rising, maybe even the CD unit getting hot.
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Old 04-18-2013, 05:19 AM
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I believe my warm control pressure is about 52-54 psi putting me in the mid 14s
Old 04-18-2013, 05:26 AM
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thats about where i am now i believe.


i just talked with the MSD guy. he would not give a definitive answer as far as impedence and coils working with other units. he did say the MSD blaster 2 coil would work with the stock CD unit. he also said to check grounds, which i need to do. i have not ruled out the MSD coil.

i also have a new capacitor for the bosch unit. i have considered just replacing it.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 04-18-2013, 05:47 AM
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ITS ELECTRICAL!

the meat of it is, its the coil wires from the CD unit.

i have also discovered something about the 930 that i dont think a hand full of people may know. but then on this site, you never know

here is the fluff:
first the + wire has a cut length ways in the wire but it is near the end, and under it and i could not see it at first. it looks like it was done with a razor blade. it was not near anything and thought maybe it was just cut.
so i ohmed them out and was getting unstable readings. BTW, remove the wires from the coil and CD to do this. after a whil e of messing with this i was thinking how could i check this out to be sure. so i made 4 short jumper wires to go from the connector for the CD to the CD unit. then i made 2 long ones to bypass the coil wires. i should have taken a pic, but i was not proud of how it looked. i had to put some thick paper between the connectors on the CD unit. they were very close and i did not want anything shorting out. then i wrapped it with tape.
i left the CD unit sitting on the shelf and thought, let me just ground it just in case. so i used one of my jumper wires with alligator clips to ground it.
so i fire it up and can tell it sounds a lilttle better. so i drive it and it seems all better, but i need to get it hot to be sure. so i drive it around, against my better judgement and i would say it is about 95%, maybe 98% better. mixture still needs to be checked. so i turn around to go home. slowly, and it cuts off. i knew it was one of my wires. i short, it was the ground. BUT!
as i am connecting the ground there are some small sparks, THEN... THE FREAKING ENGINE STARTS UP!!!! no starter, it just starts running. scared the piss out of me! and actaully freaked me out. (for seveeral years now my head feels like i am in "fog" or hung over. sometimes i have to stop and really think about what i see or what i am doing and think is this really what i am seeing).
so i get in and start driving again. well, it does it again. i left the key on, wiggle the ground wire, FROOM! its runnig again. since i am not out on a busy street, i try it again. remove the wire, engine dies, connect it, its running. first i had to think, did i hear the starter, but no!
i guess this is why porsche kills the fuel pumps then the CD unit.

got home and connected it back to original. back to the miss. did not even have to drive it.

so the million dollar question. how to fix it.
i dont want to slice up the cover on the wire harness and i hate to see 2 wires running to the CD unit, plus i am going to have to cut wires at the plug for the CD. i am not thilled about my options.

now i wonder if the original coil is bad, or......is the MSD coil that much better that it could cover up the fault with the bad wires?? i tried moving the wires around with it running and it did not change, so if anyone is thinking i moved the wires when i connected the MSD, i dont think that was the case. but i will put the original coil back in to check it.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 04-19-2013, 03:39 AM
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Quote:
Originally Posted by T77911S View Post
ITS ELECTRICAL!

the meat of it is, its the coil wires from the CD unit.

i have also discovered something about the 930 that i dont think a hand full of people may know. but then on this site, you never know

here is the fluff:
first the + wire has a cut length ways in the wire but it is near the end, and under it and i could not see it at first. it looks like it was done with a razor blade. it was not near anything and thought maybe it was just cut.
so i ohmed them out and was getting unstable readings. BTW, remove the wires from the coil and CD to do this. after a whil e of messing with this i was thinking how could i check this out to be sure. so i made 4 short jumper wires to go from the connector for the CD to the CD unit. then i made 2 long ones to bypass the coil wires. i should have taken a pic, but i was not proud of how it looked. i had to put some thick paper between the connectors on the CD unit. they were very close and i did not want anything shorting out. then i wrapped it with tape.
i left the CD unit sitting on the shelf and thought, let me just ground it just in case. so i used one of my jumper wires with alligator clips to ground it.
so i fire it up and can tell it sounds a lilttle better. so i drive it and it seems all better, but i need to get it hot to be sure. so i drive it around, against my better judgement and i would say it is about 95%, maybe 98% better. mixture still needs to be checked. so i turn around to go home. slowly, and it cuts off. i knew it was one of my wires. i short, it was the ground. BUT!
as i am connecting the ground there are some small sparks, THEN... THE FREAKING ENGINE STARTS UP!!!! no starter, it just starts running. scared the piss out of me! and actaully freaked me out. (for seveeral years now my head feels like i am in "fog" or hung over. sometimes i have to stop and really think about what i see or what i am doing and think is this really what i am seeing).
so i get in and start driving again. well, it does it again. i left the key on, wiggle the ground wire, FROOM! its runnig again. since i am not out on a busy street, i try it again. remove the wire, engine dies, connect it, its running. first i had to think, did i hear the starter, but no!
i guess this is why porsche kills the fuel pumps then the CD unit.

got home and connected it back to original. back to the miss. did not even have to drive it.

so the million dollar question. how to fix it.
i dont want to slice up the cover on the wire harness and i hate to see 2 wires running to the CD unit, plus i am going to have to cut wires at the plug for the CD. i am not thilled about my options.

now i wonder if the original coil is bad, or......is the MSD coil that much better that it could cover up the fault with the bad wires?? i tried moving the wires around with it running and it did not change, so if anyone is thinking i moved the wires when i connected the MSD, i dont think that was the case. but i will put the original coil back in to check it.
So, what you're suggesting is the remaining compression, fuel and sudden spark are "restarting" your engine? Then, it keeps running [with fuel pumps] for an indefinite period? Pretty wild!!
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Old 04-19-2013, 04:34 AM
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" ...THEN... THE FREAKING ENGINE STARTS UP!!!! no starter, it just starts running..."

Really?

I want some of that "stuff"...
Old 04-19-2013, 05:56 AM
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i dont know how it started. the key was the engine died due to lack of spark. then i connected the ground and it started running. it really freaked me out. i may have to try it again. i dont know how long you can wait from the engine dieing, but there was enough time for me to get out and open the deck lid.

i think the low compression engine has something to do with it.
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88 BMW 325is 200K+ SOLD
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08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 04-19-2013, 06:26 AM
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Pretty fricking weird. By shorting out the CDI wires as you did, I imagine you caused the capacitor to dump it's load and fire the coil. Simple enough. If you had enough unburned fuel sitting in the cylinder(s) still under pressure, then I suppose you could detonate it and 'start' the engine running. Probably a stressful way to start an engine, though.

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Old 04-19-2013, 10:32 AM
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