Jim @ EuroWerks

OK guys, I posted this awhile back. But just incase there's anyone out there who is reading now, I've got an 87 928 that is running rich. Runs fine at idle cold. After it warms up it starts to blow black smoke (rich) out of the tailpipe. I realize I am here with the car and you guys are not , but being honest I am just about to the end of my rope. These are the things that I've ruled out. Airmass, LH, NTC2 tempsensor, NTC1 also ,fuel pressure ,throttle switch, and wiring to all these, including o2 sensor. Two O2 sensors because the 1st was the cheaper replacement, second the original expensive one. I talked to Dave at 928 specialists and he suggested checking the hall sensor which is a good stab. The testplan as described a failure here would decrease ignition timing at part load and full load but did not say anything about idle. I cannot rule this out. I have been through all the grounds cleaning and resoldering and such. I spend the day looking for the ground thats going open when hot. The closest thing I found was the ground for the O2 that shows alot of resistance while running. I did not think this was it because if I unplug it I figured the rich problem would ease up. Last but not least this all started after a coolant leak sprayed coolant into the intake tube (Pass side) while driving down the interstate. I am not above giving reward and credit for help of this fix.I told you guys I'm about at wits end. So if any of you guys can help me out with the fix maybe I can help you out to!

Kevin Michael

had a similar problem but on a non porsche car. turned out to be the throttle switch/switches. loosened mounts turned them alittle seemed to get better, but replaced and it was fine. it was an lh system, i believe

Ben Allison

Jim,

Either your fuel pressure is way too high (doubt it), your injectors are getting near 100% duty cycle, or there's a leak in one or more of the injectors. Hook up an oscilloscope to the injectors and check the duty cycle.

If the duty cycle is too high, suspect wiring to the injectors, injector ground, bad brain, or faulty sensor wiring. If the duty cycle is 100%, I'd suspect ground first.

fezz

oh sh*t, time for the architect to chime in.

what about the burning coolant?
coolant burning in the combustion chamber?
exhaust valves damaged, letting unburnt fuel escape?

should i stick to designing buildings?

ErnestSw

An unplugged O2 sensor will default to a rich condition, so you haven't ruled that out.
I'd assume that the problem was fluid in the intake related and look at the top end including the injectors. Try unplugging each injector on the passenger side in turn and see whether the car runs a little rough, but with the correct mixture. That may identify a problem cyllinder. Could be plug related also.

Ben Allison

Ernest,

Good point, I had naturally assumed the plugs would be the first thing he'd check, but it's a very likely scenario. Coolant into combustion chamber = cracked/damage spark plugs. Could cause all kinds of problems.

John Speake

Jim,
The Halll sensor would not affect idle, also it would not affect mixture strength, even if the knock sensors (which it serves) registered a problem with knocks.

Does it run rich just at idle, or at other throttle settings ?

Shortly after start up, it is running open loop, you suggest that it is OK then ?

You can unplug the O2 sensor to fault find, it will default to the mid range fuelling. ie the same as a non cat car ( I just checked this on my test jig, Ernest)

If you unplug the sensor, it will somewhat simplify fault finding.

Was the MAFyou tried a new unit ?

Jim @ EuroWerks

Ernest, I have tried the disconnecting injectors I ran into this on a BM$ long ago it helped out to find the low compression problem. Ben I don't have an osiloscope but I do have acces to one. Also I've been through the ground numerouse times. John, I've tried two known good AFMs with no luck. It continues to run rich at idle and driving. Ben I was thinking down the same path as you. I was tracking down grounds and measuring them with the car running and watching the resistance. The one that is strange is the one going to the O2 gets pretty high while running. Its on the same circuit as the big ground going to the LH term 17 I think. To help find this sooner I supplied Additional grounds to any questionable terminals while running with no good results. Including the AFM . I've had the engine grounds apart and resoldered and replaced terminals including running additional ground to the pass side engine connection. Also I've replaced the main engine ground along with cleaning the strap on the body at the deck lid. In case you've havent noticed I beleive this is also a ground issue. Fezz, it's always good talking to you. Guys thank for everything this thing is killing my pride. Can anyone put a timing light on there 87 car and tell me what it's reading at Idle.

Ed Taylor

JIm, Mine reads 10 deg per the manual

Jim @ EuroWerks

What page? I might be missing that page.

Billy W

Who am I to offer suggestions to you but, have you tried a know good brain? Or since this started with the engine sucking down a lot of collant have you done a compression and leak down?

Jim @ EuroWerks

Billy, not only have I tried a know good brain, but I've also tried a Known good control unit. Done the leak down and compression ck. I guess smart rednecks think alike. As opposed to dumb red necks. Or is that good old boys?

Ed Taylor

Jim,
Don't have access to my manuals at the moment, but the spec. is also listed on the emissions label under the hood. 10 deg +-2 @ idle.

Billy W

What is the manifold pressure doing as the car warms up, is there a leak?

Jeez drive a multicolor porsche and people call you a redneck.

Old & New

Jim, I know you said you already looked at the temp2 sensor, but maybe it would be worth rechecking. The connector on mine had failed and caused the symptoms you described. Be sure to check the sensor all the way back at the brain, and maybe just replace the connector with a known good part just to be sure.