LT1 Based Engine Tech 1993-1997 LT1/LT4 Engine Related

Just scanned car, please decipher!

Old May 25, 2004 | 02:13 PM
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Question Just scanned car, please decipher!

Just scanned the car to try to determine the cause for the loss of power at high RPM's, close to 5k. Here's what I got.

5425 RPM, 45 MPH
MAP = 3.72
Throttle Sensor = 4.52, Throttle Angle = 99%
Left O2 = 796, Right O2 = 798
Left Injector Cycle = 11.3, Right Injector Cycle = 11.0
MAF = 153
CCP Duty 64.3%
Idle Air = 66 steps, Learned Idle = 21 steps
EGR = 0%
Spark Advance = 39*
Knock = 0%, Knock Sensor = 20
Closed Loop

OK, now what's this all mean? What's going on?
Old May 25, 2004 | 03:07 PM
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Re: Just scanned car, please decipher!

5425 RPM, 45 MPH *** self explanatory

MAP = 3.72 *** looks "wrong".... you are at WOT, MAP should be 100kPa or just a few kPa below barometric pressure. Yoiu shouldn't be at a very high altitude in KY, so this looks low. A 3.72V MAP reading corresponds to about 78kPa.

Throttle Sensor = 4.52, Throttle Angle = 99% **** Normal.... assuming your right foot was on the floor.

Left O2 = 796, Right O2 = 798 **** Always risky to use OEM narrow band sensors to measure richer than stoichiometric A/F ratios, but this looks LEAN. I would be looking for readings at least above 850mV.

Left Injector Cycle = 11.3, Right Injector Cycle = 11.0 **** This is "pulse width" in milliseconds, not "cycle". Normal, or possibly as little on the low side.... but then air flow looks low too.

MAF = 153 ***Looks a little low for 5,400rpm at WOT. Any chance your air filter is really plugged up? That would explain the low MAP reading as well.

CCP Duty 64.3% *** This is the canister purge stream. OK

Idle Air = 66 steps, Learned Idle = 21 steps **** Looks a little low... normally the IAC will go up closer to 100 counts at WOT/high rpm... but shouldn't be a problem.

EGR = 0% **** Normal.... EGR doesn't operate at WOT, over 3,500RPM

Spark Advance = 39* ****Looks a little agressive. I would expect something closer to 35deg. Again, spark advance it selected off a timing map based on MAP and RPM, and the low MAP may be accounting for the higher than expected advance.

Knock = 0%, Knock Sensor = 20 **** Surprised there is no knock with the extra advance and seemingly lean condition. I have to assume that the second number is "knock count" and its meaningless, since its a "cumulative" field that just keeps increasing when knock is detected and eventually resets to "0" whenh the field capacity is exceeded.

Closed Loop **** Normal... this is a "flag" that indicates that all the requirements for closed loop operation have been met - O2 sensor up to temperature, coolant up to temperature, and timer since startup has timed out. But when you go WOT, although "closed loop" is stll enabled, the PCM is actually operating in power enrichment (PE) mode.
Old May 25, 2004 | 07:55 PM
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seems like a few things
Old May 26, 2004 | 06:23 PM
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Well, took off the MAP sensor, I took off and flipped the rubber gasket on the intake side of the sensor since the rubber seemed a little worn down at one end. It fit in snugly now when putting back on. I also discovered a 2" rip in my 1LE elbow right by the clamp for the throttle body. I used some Krazy glue to seal it, then a layer of rubber sealant on the outside to make sure it sealed well. As far as my EGR, I noticed that the bolt where the hose attaches to the manifold is barely in there (I have replaced the manifold once before). I couldnt get to the bolt well enough to tighten it any further, I need a 12mm closed end wrench, which I don't have, to get to it.

Anyway, took it up the street a few times today, and I noticed no loss of power at the high RPMs. Did about 3 1st gear runs.

SO, what did I do that probably fixed the problem?
Old May 27, 2004 | 03:04 PM
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Would the tear in the intake elbow be enough to cause the high rpm loss of power and the scanner readings? I just want to be sure that it was what was causing the problem.
Old May 27, 2004 | 08:08 PM
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A tear in the air intake elbow can cause may problems. It will suck in extra air through the tear. Any air pulled into the engine after the MAF sensor will not be picked up. This will most like throw off a lot of the engine calculations. I would say it would probably run lean. I would scan it again and post the results. If i were you i would just buy a new intake elbow. I tried to fix mine once and it worked for a while but not for long.
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