Bizzare 4 cylinder running condition, suggestions?
07-19-2006, 10:52 AM
#1
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Bizzare 4 cylinder running condition, suggestions?
'89 S4 A/T, newly built motor.
The car appears to be only running on cylinders 1, 4, 5, and 8.
When I pull the plug wires off of 2,3,6, and 7 (the inboard cylinders on both banks) there is no change in the running condition of the motor. Pulling any of the other four yields an immediate and noticeable rpm drop.
When running the car is backfiring into the exhaust.
When I pull the plugs on the inboard cylinders, they are clean and wet.
All eight spark plugs fire when pulled out and grounded to the block.
The injector harness gives consistent readings from clip to clip.
I put on different plug wires, same effect.
I bypassed the limp mode function, same effect.
I've got consistent compression in all eight cylinders.
I've got fuel and fire, what's left?
Cam timing is the only other variable to the equation, but I don't see how it could make the motor run the way it is now.
Anyone every come across a situation like this?
Any suggestions appreciated.
The car appears to be only running on cylinders 1, 4, 5, and 8.
When I pull the plug wires off of 2,3,6, and 7 (the inboard cylinders on both banks) there is no change in the running condition of the motor. Pulling any of the other four yields an immediate and noticeable rpm drop.
When running the car is backfiring into the exhaust.
When I pull the plugs on the inboard cylinders, they are clean and wet.
All eight spark plugs fire when pulled out and grounded to the block.
The injector harness gives consistent readings from clip to clip.
I put on different plug wires, same effect.
I bypassed the limp mode function, same effect.
I've got consistent compression in all eight cylinders.
I've got fuel and fire, what's left?
Cam timing is the only other variable to the equation, but I don't see how it could make the motor run the way it is now.
Anyone every come across a situation like this?
Any suggestions appreciated.
07-19-2006, 11:19 AM
#2
Drifting
SO you get spark on all of the plugs plus fuel into each cyilnder? Maybe the injectors sowmhow have the right pressure, but are spraying nothing out? Somethiong blocking air getting into the cylinder so the fuel is unable to be ignited without the air in those cylinders??????
Will the engine run if the four plugs that are good are pulled out?
Will the engine run if the four plugs that are good are pulled out?
07-19-2006, 11:28 AM
#3
Rennlist Member
The fact you have spark doesn't mean they are firing at the correct time for each cylinder - so double check the plug leads are correct...
Do you have good compression on those inner cylinders ?
Timing ?
Do you have good compression on those inner cylinders ?
Timing ?
07-19-2006, 11:34 AM
#4
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Curt wrote:
Although I haven't tried that ( I will tonight), my guess is that it wouldn't.
It's running pretty rough as it is now.
One more thing that I forgot to mention. At one point, the engine appeared to run smoothly (for about 5 minutes) as if all eight cylinders were firing. But then went back to missing. The engine did this after a couple of other 928 owners pushed down on the plug wire caps while the car was running. I replaced the plug wires after this thinking that the wires must be the problem but the car runs the same with the new wires.
Thanks for the input and ideas Curt.
Will the engine run if the four plugs that are good are pulled out?
It's running pretty rough as it is now.
One more thing that I forgot to mention. At one point, the engine appeared to run smoothly (for about 5 minutes) as if all eight cylinders were firing. But then went back to missing. The engine did this after a couple of other 928 owners pushed down on the plug wire caps while the car was running. I replaced the plug wires after this thinking that the wires must be the problem but the car runs the same with the new wires.
Thanks for the input and ideas Curt.
07-19-2006, 11:40 AM
#6
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Thread Starter
Hi John.
I was hoping it was misplaced leads, but I've checked and have had others double check the routing of the plug wires and they appear to be okay. The car is running exactly in the same manner as crossed plug wires though.
I only checked the driver side bank for compression, and it was good and consistent in all four cylinders. I was concerned that the cometic head gaskets were leaking, but they are holding.
As far as timing are you refering to ignition or cam timing?
Thanks John.
I was hoping it was misplaced leads, but I've checked and have had others double check the routing of the plug wires and they appear to be okay. The car is running exactly in the same manner as crossed plug wires though.
I only checked the driver side bank for compression, and it was good and consistent in all four cylinders. I was concerned that the cometic head gaskets were leaking, but they are holding.
As far as timing are you refering to ignition or cam timing?
Thanks John.
07-19-2006, 11:43 AM
#7
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Thread Starter
It's a pretty consistent backfire Nicole. Something is definitely off. Bad cam timing would show good spark, fuel, and compression, but its odd that an entire bank of cylinders isn't off, but the two inboard cylinders on each bank. My next shot in the dark will be to pull the cam covers and see what's up. The fact that the car appeared to run smoothly for a bit makes it a bigger mystery.
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07-19-2006, 11:48 AM
#9
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Thread Starter
Hey Andrew,
Spark appears to be strong and consistent, and the plugs are new. When I pull a plug out of one of the dead cylinders, it doesn't reak of gas, but if I put it up to my nose I can smell the fuel. The plugs are wet, but not to the extent I would expect them to be. My inclination is to believe that the inboard injectors aren't firing correctly. Is there a way to get them to pulse without the engine running?
Spark appears to be strong and consistent, and the plugs are new. When I pull a plug out of one of the dead cylinders, it doesn't reak of gas, but if I put it up to my nose I can smell the fuel. The plugs are wet, but not to the extent I would expect them to be. My inclination is to believe that the inboard injectors aren't firing correctly. Is there a way to get them to pulse without the engine running?
07-19-2006, 11:48 AM
#10
928 Collector
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Adam:
They are all on the same distributor IIRC and that is driver's side. [edit: nope, not all on the same coil/distributor]
Check the rotor
Check for a distributor cap crack
Check the coil wire there (swap it)
Check the coil there (swap it)
Last possibility: final stage. Don't try to pull one off, just swap the leads. If one is faulty, just toss and replace both as a unit.
Oh one more thing: make sure your spark plugs aren't wet
They are all on the same distributor IIRC and that is driver's side. [edit: nope, not all on the same coil/distributor]
Check the rotor
Check for a distributor cap crack
Check the coil wire there (swap it)
Check the coil there (swap it)
Last possibility: final stage. Don't try to pull one off, just swap the leads. If one is faulty, just toss and replace both as a unit.
Oh one more thing: make sure your spark plugs aren't wet
07-19-2006, 11:49 AM
#11
Three Wheelin'
Originally Posted by atb
One more thing that I forgot to mention. At one point, the engine appeared to run smoothly (for about 5 minutes) as if all eight cylinders were firing. But then went back to missing. The engine did this after a couple of other 928 owners pushed down on the plug wire caps while the car was running. I replaced the plug wires after this thinking that the wires must be the problem but the car runs the same with the new wires.
Thanks for the input and ideas Curt.
Thanks for the input and ideas Curt.
That being said, all the problems are coming from the leads that cross over the front of the engine. Is there something there that could cause an electrical problem with the leads? Seems unlikely, and at odds with the pushing down part.
07-19-2006, 11:54 AM
#13
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Heinrich wrote:
I wish that were true, but they are the inboard wires on each cap.
That is what is so strange. I don't tnink there is anything mechanically or electrically that connects these four cylinders.
When limp mode kicks in, which grouping of cylinders are affected?
I'm tempted to start with fresh plugs and try again.
Fabric wrote:
This is an astute oberservation Fabric, it's the only one that fits the facts, but I don't know what could be causing the problem. The entire cable from plug to cap was replaced on each cylinder.
Thank you both for your ideas.
They are all on the same distributor IIRC and that is driver's side.
That is what is so strange. I don't tnink there is anything mechanically or electrically that connects these four cylinders.
When limp mode kicks in, which grouping of cylinders are affected?
Oh one more thing: make sure your spark plugs aren't wet
Fabric wrote:
That being said, all the problems are coming from the leads that cross over the front of the engine. Is there something there that could cause an electrical problem with the leads? Seems unlikely, and at odds with the pushing down part.
Thank you both for your ideas.
07-19-2006, 11:57 AM
#14
Supercharged
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If you have strong spark (you can hear and see it clearly), then it's not ignition (unless timing is off - but since the distributor is not adjustable, I doubt it).
I can't remember if 1989 has the ability to shut down a back of cyliders or not (i.e. has the exhaust temp sensors). Pull the cover for the LH/EZK. If you see either a red light or green light - this means that EZK has shut down half the engine to prevent raw fuel from being dumped down the cats. I would think is probably due to a faulty or disconnected exhaust temp sensor.
Edit: Oh yeah this is NOT "limp-home mode" but rather "Dumb-*** mode" per Jim Bailey.
I can't remember if 1989 has the ability to shut down a back of cyliders or not (i.e. has the exhaust temp sensors). Pull the cover for the LH/EZK. If you see either a red light or green light - this means that EZK has shut down half the engine to prevent raw fuel from being dumped down the cats. I would think is probably due to a faulty or disconnected exhaust temp sensor.
Edit: Oh yeah this is NOT "limp-home mode" but rather "Dumb-*** mode" per Jim Bailey.
07-19-2006, 12:02 PM
#15
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Per Jim Bailey
Originally Posted by Jim Bailey
The relay....Matt comments "Even though it's called 'ignition' monitoring, I think it monitors injection. One of the sets of 4 injectors is not functioning." .......... The exhaust port temperature sensors (cylinders 4 and 8 for 89, 5 and 7 for 1990> ) tell the relay that there is or is not too great a difference in exhaust port temperature. The relay then ASSUMES that the cause of the variance is an ignition failure in one half of the double ignition system. Believing that it is an ignition problem the relay then shuts down fuel injection to those 4 cylinders two on each bank which share the same coil , distributor, coil wire ,ignition secondary etc. So the relay monitors exhaust temperature BUT controls the injection. This relay / system was added in 1989 BECAUSE people were experiencing a loss of power on the dual coil cars but insisted on "trying to make it home" and the unburned fuel and air being pumped into the exhaust was burning in the exhaust and then the car would catch on fire!! But this is NOT LIMP HOME mode but really is the "If you're too stupid to stop driving when you only have 1/2 the horsepower this will help keep you from burning up the car" mode.