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Got a REAL stumper for the experts
- Thread starter FbodTrek
- Start date
No and no, it was bench tested, it tested good, no flat spots, no abnormal readings.
@ Constitution hour:
Gonna check that P/U coil next.
If it was actually running lean as sensed by the O2, it would set a code. The computer "thinks" everything is fine and dandy (no codes). I don't think the O2 sensor is reading correctly.
Being able to read the ALDL stream real-time would make short work of this.
Being able to read the ALDL stream real-time would make short work of this.
Reman dist, new set of Delco plugs!! Did you tell us the the milage? OE dist, worn shaft PU coil! cheap fix! at least you know what your doing in testin! not the replace parts till you,ve run out of parts or money!!!
Ah, ok. Did you do the IAC reset procedure?
http://www.ehow.com/how_7959677_reset-baseline-idle-gm-tbi.html
Yup, did that after setting timing/checking timing.
@ Constitution hour
Tested P/U coil, no spikes, steady at .66-.67 while cranking for a decent duration, tested 3 times.
I CAN monitor the o2 voltage, it's a single wire unit, a good DVOM can read it 
I haven't done it yet, but then it isn't coding. Pretty sure if these computers don't see a change in voltage they code.
*scratches head*
I'm gonna wait till it gets dark and check the spark strength again, doing it in daylight has never been a good indicator. i'll feel pretty damn stupid if it's a weak coil. I'm used to the feeling an engine makes when spark breaks down (I ran a built turbo Nissan for years), this just doesn't feel like a miss so much as starvation.
Thanks a load for all the input guys
I'm gonna go check timing under load with timing wire connected, just for information sake.
these types of diagnostics threads are the most fun, sometimes the 'un-solvable' problem is the best kind. Sure has kept my mind off the holidays.
I haven't done it yet, but then it isn't coding. Pretty sure if these computers don't see a change in voltage they code.
*scratches head*
I'm gonna wait till it gets dark and check the spark strength again, doing it in daylight has never been a good indicator. i'll feel pretty damn stupid if it's a weak coil. I'm used to the feeling an engine makes when spark breaks down (I ran a built turbo Nissan for years), this just doesn't feel like a miss so much as starvation.
Thanks a load for all the input guys
I'm gonna go check timing under load with timing wire connected, just for information sake.
these types of diagnostics threads are the most fun, sometimes the 'un-solvable' problem is the best kind. Sure has kept my mind off the holidays.
Sounds like a good time to have an osilliscope, I suspect disconnecting the o2 sensor is doing the same thing as disconnecting the est wire, I.E. putting it in open loop which will increase fuel mixture/ratio, which is what you are doing with propane enrichment.
Would be nice to look at data stream and ignition scope patterns, along with injector amp pattern to determine what the cause is.
Stupid question, have you checked the charging system for ac voltage? I have seen a bad alternator cause crazy running problem,ac voltage blows the ecm's mind so to speak.
Would be nice to look at data stream and ignition scope patterns, along with injector amp pattern to determine what the cause is.
Stupid question, have you checked the charging system for ac voltage? I have seen a bad alternator cause crazy running problem,ac voltage blows the ecm's mind so to speak.
I CAN monitor the o2 voltage, it's a single wire unit, a good DVOM can read it
I haven't done it yet, but then it isn't coding. Pretty sure if these computers don't see a change in voltage they code.
*scratches head*
I'm gonna wait till it gets dark and check the spark strength again, doing it in daylight has never been a good indicator. i'll feel pretty damn stupid if it's a weak coil. I'm used to the feeling an engine makes when spark breaks down (I ran a built turbo Nissan for years), this just doesn't feel like a miss so much as starvation.
Thanks a load for all the input guys
I'm gonna go check timing under load with timing wire connected, just for information sake.
these types of diagnostics threads are the most fun, sometimes the 'un-solvable' problem is the best kind. Sure has kept my mind off the holidays.
Most of the older GM's would not set an O2 code for lazy or slow operation. They had the sensor so far down the exhaust pipe they would often go into open loop at a traffic light, they would cool off, need to be around 600f to work properly. That is why the newer ones use a heater circut, get em online quickly.
Better to check spark with an spark tester that allows you to adjust the gap to tthe KV output, GM HEI should be able to jump a gap of over an inch easily.
