ribs

Nah...not really, but you probably wouldn't have read this if I had titled it differently. It did break down and needed a tow home though...$140 of bank of america's money I will be paying 14% interest on for the rest of my life was required to lift it 35 miles home. It was doing the same stuff it was doing yesterday: https://rennlist.com/forums/924-931-944-951-968-forum/177332-951-used-1-3-of-a-tank-of-gas-to-go-70-miles-bucks-at-part-throttle.html . Replacing the severed vacuum line to the fuel pressure regulator didn't seem to fix it.

Basically the car would run normally for about 20 minutes from being completely cold, then it would start stumbling at part throttle, accompanied by large clouds of black smoke. It would get progressively worse until it would repeatly buck under partial throttle (seemed to run okay at full and very low throttle) and would only run smoothly under boost. When not on boost, a huge cloud of black smoke would pour out of the back. One thing I noticed is that the car normally runs at about 50% hot on the coolant temp gauge, but was below the 1/3 hash mark when it started stumbling. It got to the point where it was undrivable, so I pulled off and waited for a tow. It stalled as soon as I took it out of gear (it was on the highway the whole time before this) and would only start for a second then die (like trying to start the car with the AFM unplugged).

Anyhow, waiting 2 hours for a tow truck driver is no fun, so I conducted a few experiments. If I would let the car sit for 20 minutes or so, it would cool down a bunch, then I would try to start it. It ran fine...for about 2 or 3 minutes, and as soon as the engine reached close to full temp, it got progessively worst with the stumbling and the such until it would just stall and not start again for a while.

I did what little diagnosis I could in the dark with no tools...thinking it was maybe a vacuum leak I pulled the vacuum line going to the bypass valve and stuck my finger over it...indeed, there was lots of vacuum at idle...~19mmHg according to my finger (and the boost gauge). Disconnecting the vacuum lines to the FPR and fuel damper seemed to make no difference. Bypassing the charcoal canister and bypass valve in the vacuum lines made no difference. I could hear no hiss or anything coming from the boost-tube fittings or the AFM to turbo hose, but it is kind of loud and my hearing isn't what it used to be.

This problem is definitely heat related...the car runs like it did when I had a blown headgasket (as in ran progressively worse as the engine temperature rises), but there is no coolant smell in the exhaust, the coolant level hasn't changed since the head was rebuilt, the coolant temp is actually lower when it runs all crappy (as opposed to overheating), and there is no cross-polination of coolant and lube. I have one of those cometic gaskets in there, run conservative boost, and have ample fueling, so I don't see this being a probability, though the way it runs is similar. The massive amount of fuel being dumped all the time makes me think something is screwy with the fuel injection, but I don't know what would progressively fail with heat.

I have the stock 2.5 bar regulator and original fuel damper still...I believe they both work just fine, but I replaced them for both more fueling and to eliminate possibilities with a problem I was having years ago. Maybe I'll try swapping these out. I think I'll go and buy a compression tester as well.

Any thoughts? I'm at a loss. It drives like it did with the blown HG, but has none of the other symptoms. I will hate this car forever if it went through 2 head gaskets in 3000 miles. Let me know whatchathink. Thanks.

Legoland951

Check your plugs. Black smoke happens when your car is running too rich. If the plugs are fouled, then you can check your AFM and other fuel related parts.

Jakerx

you need AAA buddy! it really is worth the membership fees. i've been towed off the highway once, and from my house to a shop once when i needed it...all for free!

cheetah chrome

Did you ever get all of your DME issues figured out? I remember (way back) you were having problems w/ the car cutting out and a good kick to the passenger footwell would get it running again....DME loose connections/overheating? Did you see any crossfiring when you were looking under the hood in the dark?

The black smoke is unburnt fuel so your headgasket should be ok.

PaulStewart

My 924S had this problem, after replacing a lot of parts, a used AFM finally solved the problem.

But as the factory manual says, always check the engine grounds before starting any troubleshooting.

Mike Buck

I'm no mechanic(understatment of century), but If you want to try a new AFM let me know. I have spare, brand new actually, you can borrow to test with.

My father's '89 car had all kinds of problems where it would run fine, then idle horrible and finally shut off. Not cheap, but a new AFM fixed it

HY M8NC

AFM could be a culprit, also the head temp sensor (sends a signal direct to DME), other things I've seen cause this are speed/reference sensor connections that were corroded, bad grounds, and if you can believe it the throttle position sensor.

If you just did a ton of head work, I wonder if speed and reference sensor connections are bad?

Danno

"Basically the car would run normally for about 20 minutes from being completely cold, then it would start stumbling at part throttle, accompanied by large clouds of black smoke. It would get progressively worse until it would repeatly buck under partial throttle (seemed to run okay at full and very low throttle) and would only run smoothly under boost."

So the loose vacuum hose fixed it? Then it got bad again?

Could be any number of things, but two comes to mind. One is a rip in the big rubber hose coming off the turbo. It likes to split on the back side where you can't see it, have to remove the hose to fully inspect it. The time factor is a clue as the hose won't get soft and leak until everything's warmed up.

THe other thing could be the AFM's worn out; the resistor-traces can have a worn-out track where the wiper arm sweeps. You can diagnose this by hooking up a voltmeter to the AFM's input line at the DME, pin#7, green/red-stripe wire. It should read the following:

key-on, car not-running: 0.25v
idle: 0.79-0.85v
steady-state speed, 3rd-gear/3000rpm: 1.9-2.1v
gradually stepping on the throtte: > 3.0v+

You can also measure the full-range sweep of the flapper door at a rest. Hook up the volt-meter to the same green/red-stripe wire near the AFM. Stick your hand in and slowly push open the flapper barn-door. The voltage should go from 0.25v to 4.6v smoothly with no sudden jumps or drop-outs.

ribs

I was planning on replacing the plugs soon anyways as they have 3000 miles on them and cost $0.87 a piece...but I'll pull a few plugs and see what is going on in the engine. I am 100% certain the car is running very rich after it warms as the large clouds of unburned hydrocarbons indicate.

I have AT&T (well...now Cingular) roadside assistance with my cell phone plan. They cover up to a $50 tow and will send a jumpstart to you and all that. They will reimburse me $50 for the tow as the tow company didn't accept motor club payments. They called 25 (!) different tow shops within 20 miles of where I broke down, and I suppose because of the holidays and the time (around 10) they only were able to get one shop on the phone. At least I didn't have to call information 25 times at $1.00 a pop to get ahold of a tow company. All the people who work at the call center are in Canada and say "aboot" and "ay" and all that. I always make fun of them (I've used the service to get 2 of my friends cars towed as well) for being so canadian.

Yeah, I resoldered both PCBs in the DME and have had no issues since then with cutting out or hard starting. I did thoroughly check all of the connections to the DME when I pulled it out to resolder it two years ago, and everything was gravy. There was no crossfiring...the entire ignition system is less than 3 years old (plugs changed 3 times too) with less than 12000 miles on it.

Read below for more on AFM. My engine grounds are good...I supplimented them with a 4 gauge wire that I got with my IceShark wiring/lighting kit that solved a lot of problems with my gauges and other electrical anomolies.

Cool. I'm going to probe the AFM with my voltage tester to see if all is good in the hood, and if its funky, I will take you up on that. Thanks.

I actually had that temp sensor disconnected (either by me by accident or by the previous owner...I never remember unplugging it, but when I was pulling the head off last year I noticed it wasn't plugged in) for a long time and it didn't adversely effect the way the engine ran when at running temp. I did notice after I rebuilt the head and actually plugged the sensor in that it idled and especially revved a lot better when the engine was cold in the winter, but that was it.

The head was rebuilt a little more than a year ago and this problem is new. I checked the speed/ref sensor plugs and they seemed to be fine. I did get a nifty spark tester for christmas, so maybe I'll see if its missing...

Yeah, fixing the loose vacuum line didn't seem to make a noticable difference in the way it ran, though I'm sure it was running a bit rich or lean most of the time, depending on vacuum/boost not being compensated for with the FPR.

I was going to check all of the boost fittings and other air hoses as they are probably all original and need replacement anyways. That does make sense though, as the rubber would get soft and more malliable with temp and wouldn't hold air or let air leak, throwing off the AFM calculations in the DME and making the car run rich.

Maybe tomorrow or the next day I'll probe around the AFM with the car warm (and running like crap) and see if all the voltages are within spec.


Luckily I was able to rebuild the clutch master cylinder on my MR2 today so I have something to drive around, but I'll mess with the 951 this weekend and see if I can't track down the problem. I am guessing with fair certainty that it is air metering/fuel injection related. I am sick of the old bosch electronics, so when I get some motivation I am going to ditch the stock fuel injection and install a megasquirt and EDIS so I don't have to deal with this crap any more.

Thanks!

theedge

Its "eh" NOT "ay". And ive never heard a Canadian say aboot, yet ive heard several Americans say it, that and "ruf" or something like that, instead of roof...

Thats all ive got, everything I can suggest either make minimal sense considering the symptoms, or has been suggested...

ribs

Hehe...yeah, I phorgot the fonetic spelling on the "eh". I've heard lots of Canadians say "aboot" but they were mostly western Canadians. The call center is in Winnipeg, so that is kind of mid-west. I heard the lady on the phone say "aboot" aboot 10 times yesterday when she was asking me where I was...she would say "and thats aboot 1/4 mile off of Interstate 70 (no pause)eh?"

Lots of USers (you guys are Americans too, correct? Just hyphonated americans) have lots of funny twangs. There are a few twangs in Maryland that always crack me up...like people from Baltimore County (specifically Dundalk) leave out hard consanents and instead of saying "Baltimore, Maryland" they will say "balmer, merlin". People who live south of Annapolis on the rivers tend to say "warsh", "warshenton", "wooter", "share", and "crowns" instead of wash, washington, water, shower, and crayons.

nine-44

I was just reading in the manuals about the temp sensor, I beleive the blue plug one on the block. It gave those symptoms. It said as a quick test that if you unplug it at temp, the car will go so rich it will die. I'd be looking at that pretty much first man. Just a suggestion, I did unplug dad's at temp and it died. Might be worth a try. Good Luck

theedge

I AM a Western Canadian, from the REAL West of Canada Winterpeg isnt in the west, it isnt in the east, nor really even the north or south. Winterpeg/Manisnowba is... Its like Minnesota or something.

As a side note, I find it impossible to talk to people from the South. Talk about a poor excuse for english "Hi iimmmmm froooommm Teeexaahhhsssss...."

theedge

Really? Never heard that before about testing that one...