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Username Post: 93 454 drivability problem        (Topic#245837)
ufd1233 
Forum Newbie
Posts: 19

Loc: Utica IL
Reg: 07-06-10
07-18-10 12:56 PM - Post#1947159    

I have a running problem that has me stumped. Heres the truck 1993 k3500 reg cab 454 tbi auto trans.
Heres the story, Bought the truck as a basket case from my company, It was at another facility where thier employees thought the engine locked up because it would not turn over. Someone let these clowns pull the motor, they broke conectors cut exhaust unbolted heads main bearing caps, and so on. The problem, a bearing went out of the alternator, weak battery couldn't turn it over to start. Killed a good truck.

So i bought it cheap, (stole it $400) sat with it in my shed for a year or so, not sure what to do lots parts missing. Found a 92 k2500 7.4 running truck 201,000miles wrecked, bought it. Swapped everything out into mine this winter, few snags but corrected, prolly put 400 miles on since.

The current problem, After driving long enough to go through a few heat cycles It will began to search rpm, let off throttle to coast severe surging occurs, like its losing all spark or all fuel for an instance. Sometimes dies, but always restarts. If i let it cool down and restart problem is gone but returns when it gets hot. If WOT is tryed, performace is great runs as it should, seems fine but problem returns in a few miles.

Heres what ive checked or replaced. Fuel Pressure-ok, fuel flow-ok, ignition module-replaced, CTS-replaced, TPS- replaced. Has had a code 43 since first ran in winter, replaced knock sensor, havent seen code since. Replaced ecm ground eyelets by thermostat. Tryed parts from other truck, egr, vaccum selenoid, map sensor. No difference.

Not sure what to do i tryed lots of other parts just because i have them I hate throwing parts but it seems like all im doing. I checked all the replaced sensors first with a meter. (all ok) but changed them thinking they failed when the heat arrived. Looked for vaccum leaks got nothing. Timing is good. And before the truck reaches a few heat cycles it runs very well, smooth and responsive, idles, but then the gremlin shows up.

Sorry for the insanely long first post but Im trying to give lots of info to catch everyone up to speed. Looking forward to figuring this one out.
2009 GMC 2500hd 4x4 reg cab duramax
1993 Chevy K3500 srw reg cab 7.4L


 
Low priced Genuine GM Auto Parts
355Cheyenne 
Senior Member
Posts: 3765
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
07-18-10 02:38 PM - Post#1947210    
    In response to ufd1233

Hello and welcome to Chevy talk. Did you check for vacuum leaks?
98 Silverado k1500 4x4 350


 
ufd1233 
Forum Newbie
Posts: 19

Loc: Utica IL
Reg: 07-06-10
07-18-10 03:31 PM - Post#1947246    
    In response to 355Cheyenne

Yeah checked that, I just used the carb cleaner spray down trick and got nothing.
2009 GMC 2500hd 4x4 reg cab duramax
1993 Chevy K3500 srw reg cab 7.4L


 
ufd1233 
Forum Newbie
Posts: 19

Loc: Utica IL
Reg: 07-06-10
07-18-10 03:40 PM - Post#1947249    
    In response to ufd1233

Im also reading the post with the suburban and the blinking ses light. When my truck goes into "failure mode" the light starts blinking but never sets a code. Its almost like when an obd2 vehicle has a current misfire and the light flashes. Should i suspect my ecm like the suburban guy? This truck did run fine and i have never touched it but could this be anything? Random thought. Thanks
2009 GMC 2500hd 4x4 reg cab duramax
1993 Chevy K3500 srw reg cab 7.4L


 
355Cheyenne 
Senior Member
Posts: 3765
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
07-18-10 04:12 PM - Post#1947266    
    In response to ufd1233

correct, if the light starts flashing fast, typically this indicates either a faulty ECU or a defective PROM.
98 Silverado k1500 4x4 350


 
ufd1233 
Forum Newbie
Posts: 19

Loc: Utica IL
Reg: 07-06-10
07-18-10 05:37 PM - Post#1947339    
    In response to 355Cheyenne

ok i just tryed the ecm. Didn't work, i drove the truck got it to the sweet spot and it started doing its thing, i limped it home got it in my shop still doing its thing, shut it off unhooked the battery and then changed the ecm. Restarted and it instantly started performing the same. But i did find a wire spliced in by someone. It is pin #14 on the top of the larger of the two connectors. Chased it went to the o2 sensor. (Purple wire) Had it on a scan tool last week and did see the o2 was alternating rich-lean. Never saw a code for the o2. Where does the ecm get its power and ground from? The ses light was still blinking on off rather quickly. With both ecm's.

by the way the ecm was from the motor doner truck with is a 92 k2500 auto trans 7.4 should be the same right?
2009 GMC 2500hd 4x4 reg cab duramax
1993 Chevy K3500 srw reg cab 7.4L


 
355Cheyenne 
Senior Member
Posts: 3765
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
07-18-10 06:18 PM - Post#1947363    
    In response to ufd1233

should be, you did not swap the PROMs right?

I do not know 100% for sure where the grounds are on a 7.4 but on a 5.7 they are on the thermostat hounding, front driver side head and passenger side firewall.


if it is an o2 sensor issue you could just unplug it, make sure you are getting a zero reading. Then the motor will run open loop and if the problem clears then you have a bad o2 sensor or wire harness connection.
98 Silverado k1500 4x4 350


 
ufd1233 
Forum Newbie
Posts: 19

Loc: Utica IL
Reg: 07-06-10
07-18-10 06:39 PM - Post#1947378    
    In response to 355Cheyenne

Right I didn't change proms, just plugged in the ecm as is. guess i never thought to unplug the o2 and force open loop, tried that with everything else. Ill do some looking and check grounds where you thought to look. Thanks again for the advice, even if were not solving the problem yet theres still some good info here to store in the old thinker. I might be a little while inbetween posts now, (stupid day job!) but ill let ya know. Thanks
2009 GMC 2500hd 4x4 reg cab duramax
1993 Chevy K3500 srw reg cab 7.4L


 
ufd1233 
Forum Newbie
Posts: 19

Loc: Utica IL
Reg: 07-06-10
07-18-10 08:03 PM - Post#1947420    
    In response to 355Cheyenne

kind of an interesting night, first off i unplugged the o2 sensor....no change. Check that off the list. But it took me a long time to get the truck to act up. Im thinking this is because the outside temp has gone down. It was around 90 this afternoon when i was testing it, now it has dropped considerably and it took about 9 miles for the gremlin to show. So this has me convinced its a heat related issue.

However, when in my shop the truck surging and dying, i could see it running rich from the dark smoke at the exhaust. I thought what the hell im gonna unplug the timimg wire. Started running smooth, low rpm but smooth. Plugged it back in no change, shut the truck off started back up and the surging was back, unpluged the wire, smoothed out. Did this 3 times in a row. What does that mean? I have checked base timing a while ago and it was fine. And yes the wire was unhooked when i checked it.
2009 GMC 2500hd 4x4 reg cab duramax
1993 Chevy K3500 srw reg cab 7.4L


 
ufd1233 
Forum Newbie
Posts: 19

Loc: Utica IL
Reg: 07-06-10
07-20-10 07:25 PM - Post#1948479    
    In response to ufd1233

Fixed it. Decided to swap out the distributor since i had another one from the other truck. When i removed it i found that quite a little bit of side to side play and while holding it in my hand and turning it you could feel the "square" bearing. I assume this causes my pick-up coil to fail and with increased heat it really failed. Installed the other spare shaft and drove 20 plus miles and lots of idle time, so far no issues. Feeling real confident i got it. Thanks for the help, just thought i should give a little closure to the post.
2009 GMC 2500hd 4x4 reg cab duramax
1993 Chevy K3500 srw reg cab 7.4L


 
Low priced Genuine GM Auto Parts
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