Rough Running, Volume 5
04-01-2002, 02:42 AM
#1
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Rough Running, Volume 5
OK...
I am officially frustrated.
For the past few months, I have been trying to resolve a high-throttle miss that my '85 S2 has had off and on since I bought it three years ago. The background is that I work for an airline, and am often away for weeks at a time. When I return, the car runs on 6-7 cylinders for 40 miles or so. Then it runs fine, but at high throttle/ hi RPM on hot days it starts doing it again.
I have had the ignition checked- it is fine. I have poured gallons of fuel injector cleaner into the tank; no change. Because of the ******* Bin Laden, I'm furloughed and have been driving the car quite a bit lately- I just returned from a 1575 mile round trip to Asheville, NC. I've suspected an air leak between the MAF and the intake for a while; today I took all of it apart and wrapped tape around the bottom end of the MAF sensor so the O ring would make a tight seal, and replaced portions of the vacuum line that connects the two fuel pressure regulators. I also examined the MAF sensor connector and cleaned both ends [it was very corroded], all to no avail.
After today's fiasco, it ran like crap all night. Any real throttle and it immediately began missing, keeping me from pushing the car at all. Quite frustrating....
So... does anyone have any ideas?
Normy!
I am officially frustrated.
For the past few months, I have been trying to resolve a high-throttle miss that my '85 S2 has had off and on since I bought it three years ago. The background is that I work for an airline, and am often away for weeks at a time. When I return, the car runs on 6-7 cylinders for 40 miles or so. Then it runs fine, but at high throttle/ hi RPM on hot days it starts doing it again.
I have had the ignition checked- it is fine. I have poured gallons of fuel injector cleaner into the tank; no change. Because of the ******* Bin Laden, I'm furloughed and have been driving the car quite a bit lately- I just returned from a 1575 mile round trip to Asheville, NC. I've suspected an air leak between the MAF and the intake for a while; today I took all of it apart and wrapped tape around the bottom end of the MAF sensor so the O ring would make a tight seal, and replaced portions of the vacuum line that connects the two fuel pressure regulators. I also examined the MAF sensor connector and cleaned both ends [it was very corroded], all to no avail.
After today's fiasco, it ran like crap all night. Any real throttle and it immediately began missing, keeping me from pushing the car at all. Quite frustrating....
So... does anyone have any ideas?
Normy!
04-01-2002, 09:04 AM
#2
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As a general rule, an air leak that hurts full throttle running will keep the car from idling.
I would immediately suspect ignition, starting with a bad coil wire or a bad coil. A bad plug wire or plug is also a possibility.
I would immediately suspect ignition, starting with a bad coil wire or a bad coil. A bad plug wire or plug is also a possibility.
04-01-2002, 11:03 AM
#3
Three Wheelin'
Normy,
I had a coil wire that was sometimes arcing to the trans cooler line near the radiator. This was quite random but I could see a slight burn in the metal line. I found this by doing a "lights out" test in my garage. Engine Start engine, darken garage and look for arcing.
Just a thought,
Greg
I had a coil wire that was sometimes arcing to the trans cooler line near the radiator. This was quite random but I could see a slight burn in the metal line. I found this by doing a "lights out" test in my garage. Engine Start engine, darken garage and look for arcing.
Just a thought,
Greg
04-01-2002, 12:43 PM
#4
Chronic Tool Dropper
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I'll second the suggestion to look at wires, especially if the age of your wires is greater than maybe 50k.
On my parts chaser/boat tow/family limo Explorer, I chased and hunted and sleuthed and etc for the same high-speed miss you are experiencing. I decided that a systematic diagnosis was in order, and that extended the 'cure period' out over a couple weekends. Plugs renewed, no change. Removed the wires, checked with meter, all OK by that method, Hmmm. Plugs all looked fine with no bright-whites, no sooty ones, the signs of lean run and misfire, respectively. Replaced the wires anyway and all was fine. After carefull cleaning and inspecting, I could see one place where I might have had an arc-through. Since the new wires were installed, I decided not to continue the systematic diagnosis all the way to swapping the old wires in one by one. Since that initial problem, the wires have deserved replacemnt like clockwork every 50-60k.
On the 928, besides the wires, there are also cap(s) and rotor(s) to consider when chasing high-speed miss problems. Most rotors seldom go bad, except maybe some of the centifugal regulator types. Caps develop cracks, have problems with carbon tracking, have the center carbon wiper get lost or worn out, etc. Sometimes a careful inspection will reveal the problem, sometimes not.
The temptation on ignition problems is always the shotgun aproach: plugs, wires, caps, rotors, and sometimes even coils. In furloughed state I know you are cash-flow concious, so cover the obvious/least costly stuff first. New plugs will temporarily mask other system weaknesses, so use your judgement on when to do those in the sequence.
Much as I love having the hood up, I mostly tend to do ignition stuff on a prophylactic basis these days. I'm probably due for wires/caps/rotors on the 928, just need to budget the time. The coils on the later cars are a known weak spot, so my shotgun might have those in it too. Seems like there's always a list of things to do if I want to. It's part of the joy of owning a 928.
On my parts chaser/boat tow/family limo Explorer, I chased and hunted and sleuthed and etc for the same high-speed miss you are experiencing. I decided that a systematic diagnosis was in order, and that extended the 'cure period' out over a couple weekends. Plugs renewed, no change. Removed the wires, checked with meter, all OK by that method, Hmmm. Plugs all looked fine with no bright-whites, no sooty ones, the signs of lean run and misfire, respectively. Replaced the wires anyway and all was fine. After carefull cleaning and inspecting, I could see one place where I might have had an arc-through. Since the new wires were installed, I decided not to continue the systematic diagnosis all the way to swapping the old wires in one by one. Since that initial problem, the wires have deserved replacemnt like clockwork every 50-60k.
On the 928, besides the wires, there are also cap(s) and rotor(s) to consider when chasing high-speed miss problems. Most rotors seldom go bad, except maybe some of the centifugal regulator types. Caps develop cracks, have problems with carbon tracking, have the center carbon wiper get lost or worn out, etc. Sometimes a careful inspection will reveal the problem, sometimes not.
The temptation on ignition problems is always the shotgun aproach: plugs, wires, caps, rotors, and sometimes even coils. In furloughed state I know you are cash-flow concious, so cover the obvious/least costly stuff first. New plugs will temporarily mask other system weaknesses, so use your judgement on when to do those in the sequence.
Much as I love having the hood up, I mostly tend to do ignition stuff on a prophylactic basis these days. I'm probably due for wires/caps/rotors on the 928, just need to budget the time. The coils on the later cars are a known weak spot, so my shotgun might have those in it too. Seems like there's always a list of things to do if I want to. It's part of the joy of owning a 928.
04-02-2002, 12:46 AM
#5
Dr Bob -
I have had very good luck with replacing the coils with the venerable "MSD" coils from the summit catalog. I did this on my previous 924S, and I just did it on my S4. I switched them back and forth on the 924S, with no noticable change, so I have not tried changing it from the MSD coils in the S4. If anyone has any dissention on this, please speak up. The 35 dollars each beat the 60-70 dollars each for the bosch ones. They are smaller in DIA., so I make sure they are snug with a "filler" in the bracket.
I have had very good luck with replacing the coils with the venerable "MSD" coils from the summit catalog. I did this on my previous 924S, and I just did it on my S4. I switched them back and forth on the 924S, with no noticable change, so I have not tried changing it from the MSD coils in the S4. If anyone has any dissention on this, please speak up. The 35 dollars each beat the 60-70 dollars each for the bosch ones. They are smaller in DIA., so I make sure they are snug with a "filler" in the bracket.
04-02-2002, 09:38 AM
#6
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From the Workshop Manual, page D 24/28-3:
"Important Vehicle information"
"The specified coil (refer to order number) must not be replaced by a different coil."
YMMV
"Important Vehicle information"
"The specified coil (refer to order number) must not be replaced by a different coil."
YMMV
04-05-2002, 09:13 PM
#7
Norm,
Have you worked thru the high speed miss recommendations yet?
As a last resort - time consuming but not expensive - there might be some 'minor' crud blockage between the tank filter and the output side of the fuel pump. Not noticeable at low and middling speeds but when the old, aluminum, 8 banger starts to roar the reqirement for fuel puts demands on the fuel system at the upper range of its capeabilities. Maybe Wally, Cat. or the others could give you the straight skinny on this. But, I think If the neighbors will put up with you... run her up the tach. scale in neutral.
Would be nice if you had a super accurate tach., and more than likely the miss will occur at a different rpm than when you are driving since the engine will not be loaded. I can't think of another method unless there is a 929 engine speed ,fuel consumption graph out there - don't hold your breath - used in conjunction with a fuel meter from NASA. It is a thought ...
Good luck on this one.
John S. & Pattycakes
Have you worked thru the high speed miss recommendations yet?
As a last resort - time consuming but not expensive - there might be some 'minor' crud blockage between the tank filter and the output side of the fuel pump. Not noticeable at low and middling speeds but when the old, aluminum, 8 banger starts to roar the reqirement for fuel puts demands on the fuel system at the upper range of its capeabilities. Maybe Wally, Cat. or the others could give you the straight skinny on this. But, I think If the neighbors will put up with you... run her up the tach. scale in neutral.
Would be nice if you had a super accurate tach., and more than likely the miss will occur at a different rpm than when you are driving since the engine will not be loaded. I can't think of another method unless there is a 929 engine speed ,fuel consumption graph out there - don't hold your breath - used in conjunction with a fuel meter from NASA. It is a thought ...
Good luck on this one.
John S. & Pattycakes
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04-05-2002, 10:16 PM
#8
Chronic Tool Dropper
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The simple/quick/easy way to do this is to install a fuel pressure gauge on the end of a hose, and run that hose up to the top of the hood so you can see it while you drive. Do whatever it is that brings on the miss, and watch the pressure. If it falls off much under high load, you have a starting point.
A reminder to NEVER plumb a pressurized fuel hose inside the car. Up there where you can see it through the windshield will be fine.
A reminder to NEVER plumb a pressurized fuel hose inside the car. Up there where you can see it through the windshield will be fine.
04-06-2002, 02:23 AM
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Hey-
I started the car up in the garage last night and guess what....a little blue flash was seen intermittently between the coil wire and one of the plug wires. I didn't want to run the engine up to speed in the garage, but I bet that the plug wires are at least part of the problem. Thus...I dropped three bills for a set of Nology wires yesterday from the folks in North Carolina.
Will this solve the problem? I know one way to find out! I'm at my whits end. If this doesn't work, then I've got some kewl red wires, but I think it is time to talk to the people at Zotz garage in Orlando. I printed out Wally's description of how to test the MAF and the throttle switches, so I'd do that first I guess.
It's gonna have to wait though- the Sun N Fun airshow is this weekend, and the shark is going to be transportation only!
Normy!
I started the car up in the garage last night and guess what....a little blue flash was seen intermittently between the coil wire and one of the plug wires. I didn't want to run the engine up to speed in the garage, but I bet that the plug wires are at least part of the problem. Thus...I dropped three bills for a set of Nology wires yesterday from the folks in North Carolina.
Will this solve the problem? I know one way to find out! I'm at my whits end. If this doesn't work, then I've got some kewl red wires, but I think it is time to talk to the people at Zotz garage in Orlando. I printed out Wally's description of how to test the MAF and the throttle switches, so I'd do that first I guess.
It's gonna have to wait though- the Sun N Fun airshow is this weekend, and the shark is going to be transportation only!
Normy!