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In Reply to: Re: I love a challenge but... posted by Keith on July 02, 2001 at 20:30:41:
2) checked for intake gasket leaks by spraying the areas with some type of combustible fluid (not sure what he said). Said that if the engine began to run differently that you would find a leak this way.
If there is a leak, extra combustable gas would get into the cylinders and the engine would try to increase RPM's. I assume he checked more than just the intake manifolds for leaks and found nothing?
3) checked fuel pressure and entire fuel delivery system
Did he pull the regulator vacuum line and see if the pressure came up? What were the numbers and more important, were they the same from side to side?
4) checked the IAT - not sure about switchnbait
There is an IAT sensor at the back of each intake air manifold. Don't know if the cables would reach to allow you to switch...likely need to physically switch sensors from one side to the other. What were the numbers and more important, were they the same from side to side? An open circuit, high resistance, would be the problem one since it would be telling the DME that the air is colder than it is.
5) not sure about checking the fuel injector solenoids...is there a procedure for this?
There is a resistance measurement that can be done. Unfortunately my Bentley is at work...I will post values tomorrow but for now, finding one or two different from the rest would give you a good indication. Also place the end of a big screwdriver between the injector and your ear and listen to what the injector is doing - you would be suprised at how clearly you can hear what is going on inside. Again, you would be listening for obvious differences between one or two injectors and the rest.
6) checked the MAF but did not do switchnbait
What did he check for? What were the results of his check? Did he look to see if the hot wire did its one(?) second burn on shut down? I think not switching would be a mistake here (assuming the cabling will reach when the socket ends up on the other side of the MAF from where it normally is).
7) checked output of O2
What were the results of the output? Did they both behave the same? Were they oscillating between 0.2V and 0.8V? Did they oscillate at about the same frequency? Did he try switching the wires from one to the other? If both O2 sensors were reading the same and one bank was rich, then there is something wrong with the sensor. It should be sitting/oscillating at the high end of the range, somewhere between 0.6V and 0.9V. If it is stuck on the low end, 0.2V to 0.5V, and running rich, then the O2 sensor is likely causing the problem. Also the wiring can cause a difference between what the sensor is putting out and what the DME is getting. It is fairly important to get accurate information on this one.
8) checked the ECT
Did he check the actual resistance of both thermocouples in the plug, or just the continuity? Did he do it while both hot and cold?
9) not sure about the spark sensor coil...what is that?
Again, my Bentley is not here but, there is a pickup coil on the spark plug wires for #6 & #12 cylinders. When these plugs are fired, the current induces a voltage in these coils and tells each DME that its bank is firing. If these coils are giving weak/intermittant signals, the DME would intermittantly shut down the bank. My guess is that this is not it - you would see rich exhaust but you should also have hesitation, missing, etc. and likely an EML, TRANS PROGRAM, etc. indication in the display and you didn't mention any of those happening.
10) checked the coil output when hot
Did he measure the resistance of the primary and secondary coils to see if they were within spec?
11) not sure about what was done with distributor rotor...have to assume that since the plugs were changed this would have at least been inspected.
12) As mentioned performed switchnbait with EML and DME
13) All plugs were of the same condition when pulled.
What condition was that? If one side was running rich, it should have shown up different that the normal side - or did you mean all 6 on the bad side were the same? What 'same' were they - black and carboned up? Did you see them yourself? I have a link below to a web site (again at work) with pictures of various plug conditions - I will post it tomorrow and if you saw the plugs you can have a look and let us know what you saw (both sides).
I am beginning to suspect that maybe the spark plug wires may too old. The mechanic did not want to do a switchnbait with these for fear that he may damage the other cars wires. Seems they get fragile when they are old, and they are very expensive for this car ($280 for left bank and $340 for right). Is there any way I can test these (maybe resistance) or possibly a cheaper aftermarket version.
Yes, again out of memory but, the total resistance of each wire should be about 6,500 ohm - I believe the split is 500 (wire) + 6,000 (resistor) on the plug end of the wire (again will post actuals tomorrow). Regardless of the actuals, you should be able to spot problems if one or two are much different from the rest. From what I have read here, there are few after market wires that can stand up to the test but if you do a search in the archives, you can find some more information on this.
'88 750iL
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