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CPT KAOS
 
LeftCoastErik's Avatar
 
Join Date: Mar 2015
Location: Livermore, CA
Posts: 411
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Starts fine, within 5 mins driving is popping..can drive through it?

MY new-to-me 951 fires right up, no matter what the temp. It has been quite cold here recently and I have just started driving it, so I don't really know all the quirks yet.

After taking off, and within 2-3 minutes, the car will stumble, pop, backfire, etc. Guessing its rich. You can drive through it, depress clutch and "clear it out" and continue. It will do this for maybe a minute and then its perfect.

I am thinking its temp sender related as my dash gauge reads lower than it should. It never gets past 1/4 warm, but it does range from really low to that 1/4 mark but no higher.

Thermostat, water pump, timing, balance, drive belts are all fresh.

Thanks and Merry Christmas
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Erik- RGruppe #743
1980 SportsPurpose 911SC "CPT KAOS"
1986 951 "CPL KAOS"
http://forums.pelicanparts.com/porsche-911-technical-forum/889856-my-new-911sc-journey-get.html
Old 12-24-2017, 07:12 AM
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Popping and backfiring are symptoms of running lean, not running rich. Look for a vacuum leak.

And, quite cold in Livermore, means, what, 50 degrees F?
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Old 12-25-2017, 06:53 AM
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It’s been in the mid 30s in the morning. It’s got something to do with the warm up cycle. I’ll smoke check when I’m back at the shop later this week
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Erik- RGruppe #743
1980 SportsPurpose 911SC "CPT KAOS"
1986 951 "CPL KAOS"
http://forums.pelicanparts.com/porsche-911-technical-forum/889856-my-new-911sc-journey-get.html
Old 12-25-2017, 08:00 AM
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Also check your wiring harness ends right before the plugs, specifically the throttle
Position sensor, air flow meter, reference and speed senders right at back of intake
Manifold, 4 x fuel injector plugs and the computers water temp sender on cylinder head right in front of intake and behind airbox these usually have cracked and crumbling jackets in the wires and exposed copper where they are bent and you sant see it unless you peel back the black rubber boots that go up around plastic plugs. Iíve/we have all had shorts in this location that trip the computer out and cause some weird intermittent issues!
Old 12-27-2017, 09:14 PM
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Also check DME temp sensor and wiring. It's the Blue plug in the valley near #1 spark plug.
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1988 951 Alpine White, AutoAuthority chip, HRE custom wheels, 10 speaker panels, Schnell short shifter, M030 sways, Koni Sports
"You're the best I ever had" --JJ Cale
Old 12-28-2017, 06:13 PM
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Yeah, test impedance of BOTH the ECT near #1 plug and the IAT in AFM. Both tells ECU outside and engine temps and it adjusts fuel-enrichment correctly.

When above posters says "check", they mean measure resistance-values of AFM flapper-door, TPS, speed/ref sensors, injectors, etc. Measure at components themselves AND at DME connector to verify that wiring in between is OK. A LOT of times, testing at components shows OK, but at DME is not OK due to crispy frayed wiring .

Also measure intake-manifold vacuum at idle with cold and then with warmed-up engine. What are these readings?
Old 01-15-2018, 10:34 AM
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I swapped the o2 sensor. That made a HUGE difference and basically eliminated the big issue.I also found the main ground all nasty and replaced it and cleaned the area. This didn't seem to do much. do have an ECU and a Cluster temp sender coming, as well as a fresh set of injectors and a 3.0 bar FPR. Hopefully that takes care of any remaining issues.
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Erik- RGruppe #743
1980 SportsPurpose 911SC "CPT KAOS"
1986 951 "CPL KAOS"
http://forums.pelicanparts.com/porsche-911-technical-forum/889856-my-new-911sc-journey-get.html
Old 01-15-2018, 03:30 PM
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Are your chips mapped specifically for 3-bar? If not you'll want to use factory 2.5-bar FPR
Old 02-18-2018, 11:36 AM
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Popping and backfiring are symptoms of running lean
Old 02-24-2018, 03:54 AM
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It was a combo of issues. Mostly a really wasted O2 sensor. Runs great now. Chips are not mapped 3bar but with the MAF kit and big catless exhaust itís happy
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Erik- RGruppe #743
1980 SportsPurpose 911SC "CPT KAOS"
1986 951 "CPL KAOS"
http://forums.pelicanparts.com/porsche-911-technical-forum/889856-my-new-911sc-journey-get.html
Old 02-24-2018, 07:09 AM
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