2001 xtreme with 5.7 vortec, finally down to 2 problems (drivablity wise). Cruising at a steady 30mph, turn the a/c off and then back on, feels the same as turning off the engine for a second. The voltmeter and oil pressure drop about 25% and stay like that whenever the a/c is on. So the voltmeter at idle no loads says 13.5v, turn on the a/c it drops to say 11v, then back to 12ish. Oil pressure drops about 3 notches and stays. At the battery, no load 14.4v, turn on the a/c down to 13v and back to 14.2v. Scanner says 11.5v, which was 10.5v before changing the icm. First replacement icm, $65 delphi, would barely run and showed zero volts on the instrument gauge. Daily driver is a stock 2000 jimmy and understand a bit of an rpm change turning on the a/c, but nothing like this blazer. It does have dual electric fans drawing 10 amps each, probably not helping.

Issue 2. One P0300 multiple misfires. Did the normal, plugs, wires, new dizzy, o2 sensors, coil and icm. If you drive the car "normal", no issues, no check engine light. You let it idle for 10 mins first startup, it throws the light. And I can see the misfires on the scanner. The short term trims up and down fairly normal looking under 3 both ways, long term banks creep up to around 7ish and vacuum reading around 12. If you just drive, no issues runs ok, except over 4500 rpms and starts to backfire and lose power. I don't know the cam, not stock for sure. Thought MAP, unplug it, runs worse. Then maybe the spider injection, but it's fairly new upgrade and it's effecting all the cylinders (except #1, which doesn't misfire nearly as much). No egr, delete plate and pluged. Might have a slight exhaust leak, shorty hedmans. Thinking vacuum leak, I can't see that effecting above 4500 rpms. Plus smoke test didn't show anything. Going to double check the diz cap today.

As I put all this in writing, I'm starting to think it might be a computer issue (411 I believe that been reprogramed to at least raise the rpm and egr delete), kind of looks like one of those ebay specials. Or an issue with MAF, even though the scanner numbers look normal. Usually not a parts changer, but really don't know the history of this build and did need the parts, except maybe the o2's. I might just drive it for a week to get in some miles, see what pops up. It does seem to run better after the tuneup, or maybe because it's not 110 in phoenix. Thanks for any help.

 

Made a utube video, power braking in gear, at idle it's not noticeable as much. Just checked the computer, it's sending info to turn on the a/c compressor and speed up the idle. But the engine cuts out for a second. The is a couple second delay the first time turning on the a/c. The fans are already running. Check engine light is the p0300 misfires

 

Just ran a test, unplugged each device one at a time, compressor, cooling fans and blower. The blower was the biggest current draw, engine drop pretty good. The comprssor has a bit of a soft start, so the motor revs a bit as it kicks on. The cooling fans are probably the best/newest wired, so not much difference even though they pull 10 amps each. So 40 amps total running, don't know the spike amps. Think I'll try a seperate relay for the blower, and just use the factory relay to turn it on. At least see what happens.

 

There is a lot to unpack here so lets get started.

1) Are there any other codes besides P300? Its uniformly cylinders 2-6?

2) What is your CMP retard? I dont know how the cam change affects this but lets look at it. Are there carbon traces and arcing under the old distr cap? If the CEL will come on revving in park then mist with water in the dark and look for arcing.

3) Is the AC the only thing that causes this engine cutoff? Does this also happen at idle?

4) What is your ignition voltage to the ICM at the moment of engine cutoff?

5) Fuel trims must all be reported together, all 4 values with sign. What are they at idle and at 2500 rpm all in park?

6) Does this still happen with the electric cooling fans unplugged?

7) Is this a stock alternator or has it been upgraded for higher output?

8) Does the truck start with a higher idle when started cold and then creep down during warm up as expected?


George

 

Just figured out the a/c surge/cutout, no body to battery ground. I was wondering why the blower seemed weak, figured it was a cheap replacement, blows good with a jumper from firewall to battery. Number one rule with electronics, check the grounds. Since cars don't usually rust in phoenix, check to make sure they are there. The joys of working on someone else's build

GeorgeLG, I'll need to add a body ground, check the pcm ground and supply, and rescan.

 

Glad you figured it out.

George

 

Couple nice long drives today, good news running way better, it's got one or two little stumples/hickups at 4000rpms and then zips up to 6300. Last week couldn't get past 4500, backfire like crazy. Check the codes half way thru the drives, got codes p0300 misfire and p0102 low voltage/freq MAF (brand new MAF yesterday). Now I've seen the p0102 before, but was thinking because I was unplugging it to test. Second drive got code p0171, lean bank one, maybe drivers side exhaust leak (some of the flange bolts were loose). So need to check MAF wiring (probably a ground) and exhaust leak.
Georges questions;
1. Scanner having trouble reading misfires with new MAF. I noticed when the MAF is unpluged, the scanner doesn't read the misfires at all. When I retured from my drives scanner didn't show any misfires, restarted the engine and they returned. Cylinders 2,3,4,5,6,7 are close say 25 misfires per cycle (think it's 30 second cycle, I've have to check) 2 and 7 being being the worse. Cylinders 1 and 8 will be single digits.
2. New distributor ( I did have a cam/crank code couple weeks ago, so just replaced it). I didn't like the cap that came with the distributor and the old one looked good, didn't see any wear or tracks. I do have a new one coming tomorrow, since everything else is new. CMP is 1.
3. Fixed, no grounds
4. I never checked, bought some backphrobes so can check this and the MAF.
5. Both short terms seem normal to me, bouncing around plus/minus 3. Long term trims at steady freeway speed (around 2500rpm), way high at 25 to 29. At 35 to 40mph (everything really warmed up), bank 1 around 23, bank 2, 18 and that tripped code p0171. What I don't like is the long term trims can change within seconds, which doesn't make sense to me. Last week, I saw them drop 10 points just coming to a stop.
6 and 7 fixed
8. Jumps up to 1400rpm at every startup, I believe it just started doing this after fixing the grounds.

I believe this has an ebay moded computer (think WARR), that isn't monitoring everything. Couple weeks ago, it ran like it had a huge cam and 1250 dominator and would load up at low speeds and all most die at idle. Now it's at least drivable. I'll see if I can take a video the fuel trims.

 

Lets break this down.

Fuel trims: The computer has a table and each location is called a fuel cell. Each cell relates to a different driving condition. As you drive around and change loads and rpms the computer keeps switching to different cells so the trims will flop all over the place. Each cell has its own LTFT stored and updated (slowly). The best initial information are all 4 trims together at idle and 2500 rpm, in park.

Any time you get a code for a sensor it can be the sensor, connector, power, ground, wire, engine computer, ... On older trucks its the wiring as often as it is the sensor which is why any good mechanic will check all those other things before firing off the parts cannon and install an inferior aftermarket part. All the computer knows it that its getting garbage MAF levels but it has no idea why. We need to check the wiring. You always start with the net voltage to the sensor while plugged in and running. Back probe pink and blk/wht and chage rpms and see if the net power is good. If that OK then we check the integrity of the yellow signal wire. Do you have any freeze frame data with that code?

Does it jump to 1400 when the AC turns on?

George

 

1400ish with a/c on. Last start, no a/c little bump over regular idle speed. Video of the fuel trims sitting in the driveway. Short term better going down the road.

 

Watching the video, looks like the o2's are going lean when I accelerate...