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

the devil just setup shop in my LT1

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Old Jan 4, 2006 | 06:17 AM
  #46  
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Re: the devil just setup shop in my LT1

Ohm from the end that plugs into the opti all the way to the black PCM connector. The purple/white wire on pin 20. Just in case you have a contact problem, but not a wire problem. Connect the wires back up. Put your voltmeter on DC volts. Put key on engine off and rotate the engine by hand while backprobing the purple/white wire to ground. As you rotate it, it should switch between close to 5volts and zero.
Old Jan 4, 2006 | 06:33 PM
  #47  
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Re: the devil just setup shop in my LT1

started mucking with it some more today, i decided to let it run from start to finish with the PC hooked up to it monitoring.

it runs fine till it is fully warmed and idled down.. apx 700 seconds coolant temp was 176.

started freaking out and tossed out a codes in this order

36 HI RES
16 LOW RES
42 something GROUNDED

car off.

Last edited by hey01; Jan 4, 2006 at 06:56 PM.
Old Jan 4, 2006 | 07:17 PM
  #48  
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Re: the devil just setup shop in my LT1

The 42 is a code for IC signal to the ICM for firing the coil. It is dropping out due to the lack of hi and low res signals. It would appear that you are having a heat related failure. It would also appear that either the optical sensors in the distributor are failing or the PCM is failing.

I suggest you test it while it is stone cold. Start it up for no more than 5 seconds to be sure it starts ok. Now break out your hair dryer. Since it's much harder to get to the distributor, warm up the PCM with the hair dryer to the point of not being able to touch it comfortably with your finger. Now crank it up and see what it does. While you do that, place the multimeter between the purple/white wire and the pink/black wire. This is a square wave but the meter set to DC can't react fast enough. So set the meter to AC and look for any value and that it stays constant. Now if it is immediately running crappy when you start it, chances are the PCM is shot. So in that case you let the PCM cool down and try the engine again quickly. Then reheat the PCM and test as before to double check the PCM is going wacky when heated.

If heating the PCM does not cause the engine to run crappy, let it run until it gets hot and does crap out. All the while watch what the meter does while it's on the hi res signal line. If it goes toward zero when it starts to run crappy, it's the optical sensor in the distributor that is heat soaking and the opti will need to be replaced.
Old Jan 4, 2006 | 07:24 PM
  #49  
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Re: the devil just setup shop in my LT1

i'll be on that tomarrow evening :-P



i forgot to mention that every time this happens it does the same A.I.R pump cycle on off on off on off and it sounds like it calls the fuel pump on off on off on off at the same time.... then it makes the crazy zzzzzzzzzzzzzzzzzzzap that sounds like it comes from the injector rail but it never does it long enough for me to pin point.

sometimes when i just turn the key to start all of this will start as well...but after letting it sit for 4 mins or so i can crank it. It is def heat related... hair dryer time!
Old Jan 5, 2006 | 05:11 AM
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Re: the devil just setup shop in my LT1

Well if the fuel pump were commanded off, the engine would shut off immediately. What's interesting is the DTC 16 shuts down the fuel pump and the injectors. The DTC 42 will shut down the injectors. So I'm curious how long it is running after the codes are set.

Another thing. It's hard to tell from what you described if the problem is consistant enough to be considered only a heat related problem. In other words, I'm not convinced that it ISN'T a wiring or contact issue yet. Your testing should help to determine that.

It would appear that the distributor is the culprit but we want to be absolutely sure before diving in. The reason I say that is, because of the location of the PCM, it's going to take a lot longer to heat up. But we don't know how warm is too warm to start breaking down, so we test. If the PCM is the bad guy, it is more than likely the voltage output to the distributor that supplies the optical encoders with voltage. That is why both hi an low res are dropping out.

You could monitor that voltage with the meter set to DC and watch it to see if it drops out when the car goes flaky. It can be seen between the red and the pink/black wire.
Old Jan 5, 2006 | 07:02 AM
  #51  
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Re: the devil just setup shop in my LT1

it will studder and freak out untill it just dies, if I don't touch the key and let it sit that is when all the werid electrical things happen. it will carry on for maybe 15 seconds and end with a buzzzzzzzzz zzzzzzz sound. Then as far as i have tested it will not crank back up untill the key turned OFF.......let it chill for a min or so then crank.





As far as random going this isn't random anymore....it started out random but now it I dupilcate the problem in 700 seconds every time.
Old Jan 5, 2006 | 07:39 PM
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Re: the devil just setup shop in my LT1

okkkkkkkkkkkkkk so heated the ECU... no dice, hooked the vmeter up to the wires and got a constant voltage everything looked fine. car ran for 1000 seconds before it started freaking out.

16 LO RES
36 HI RES
41 EST OPEN

then after trying to crank it and get it going it would crank shut off and wig out some more and it tossed some more codes

18 NOT USED
51 PROM/FLASH ERROR
46 FUEL ENABLE FAILURE


car will not crank right now letting it chill for a few mins
Old Jan 5, 2006 | 07:46 PM
  #53  
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Re: the devil just setup shop in my LT1

ummmmmmm

i just went to go crank the car. I did leave the computer hooked up to the car but the key was out and it was off, i cranked the car over and............ no codes, it seems it cleared its own codes. then it cranked perfectly.

then

BOOM again

16
36
42
and a new one
33 MAP HIGH
51

im trying to get a video of the crazy under hood action.
Old Jan 5, 2006 | 08:36 PM
  #54  
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Re: the devil just setup shop in my LT1

http://home.comcast.net/~jodom0101/LT.mpg

damn it the cam didn't pick up the zapping sound i guess it was to high of a freq but it sounds like the injectors and i was resting my hand on the fuel lines and could feel the vibrations from it.

the ECU actually cooled down from the hair dryer so it isn't really hot, but it seems the longer i try to keep pushing it to run the more pissed off it gets.

after letting it sit for 1 or 2 mins i just put the key in and turn the ign to ON...and all by itself the air pump and fuel pump come on together.. sometimes just for a split second, sometimes over and over.
Old Jan 5, 2006 | 09:12 PM
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Re: the devil just setup shop in my LT1

It sounds like to me you have the problem of too much AC on the DC line. That is perhaps the diodes are breaking down in the alternator and allowing AC through on the DC supply line. When you start it up, measure from the alternator ouput to the neg terminal of the battery with the meter set to AC. You want 0.03 VAC or less. If it's over that, the AC leaking out of the defective alternator is causing fits with the PCM.

It does appear that the 16 and 36 are consisitant. It could be that when you start to have the ignition problem, it runs slow enough to start effecting the speed and therefore output of the alternator. This seems that it "browns" out the PCM. So we still have to determine if its the opti or the PCM. Check it as I mentioned and see what you find.

The video was useless on my viewer.

Last edited by Guest47904; Jan 6, 2006 at 05:29 AM.
Old Jan 6, 2006 | 08:53 AM
  #56  
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Re: the devil just setup shop in my LT1

having an underdrive pully probably doesn't help the speed of the alt during the muck up as well. The alt does have 95,000 miles on it though.
Old Jan 6, 2006 | 11:12 AM
  #57  
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Re: the devil just setup shop in my LT1

Sounds like your fans not your air pump. I've got a rebuilt opti and harness I'd let go for cheap just to see if it changed your problem any. PM me if you want it.
Old Jan 6, 2006 | 05:12 PM
  #58  
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Re: the devil just setup shop in my LT1

well the fans came on that time but the more high pitched motor is the AIR pump.
Old Jan 6, 2006 | 06:50 PM
  #59  
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Re: the devil just setup shop in my LT1

OK i got a good video of it now! HA!

ALT checked ok the whole run it stayed at about 0.01 but if i wiggled my hand the meter would jump around ( stupid digital mulit meters)

anyway i ran into 1000+ seconds before it went crazy, it was just idleing and it started up ran for 100 seconds untill it gave up.

this is where it gets good.

i turned they key and it started its normal AIR pump b/s then it stopped i cleared all the codes from lastnight. went to go crank the car. turned the key to ON and it did the AIR pump rev crap and THE TACH WAS MOVING WITH IT.

the car tossed a 36 and 33 WHILE NOT RUNNING!!!!!!!!!!!!!!!!!!! and the tach was jumping almost in sync with the AIR pump fit.
Old Jan 6, 2006 | 07:22 PM
  #60  
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Re: the devil just setup shop in my LT1

ok its toast again, cranked up and ran ok for about 130 seconds. I noticed it was running in closed loop.

it freaked out and died

tossed a 51

its the same 36, 16, 42,or 51 over and over again.


new vid

http://home.comcast.net/~jodom0101/fds.mpg

right click save as



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