GMC 3500 - starts when it wants & tranny crazy

Lariat · 08-24-2008, 11:04 AM

I have a 1999 GMC 3500 van w/ a 5.7L engine. My truck has been running fine but every now and then, and more so recently, it will start when it wants, cold or hot, and the transmission on one day is fine and another won't drive faster than 30 mph with a crazy speedometer that reads 55-110. I think it's linked for some reason. I replaced the fuel filter and the battery and it seemed to do the trick, but in two days someone borrowed it to go two miles, they got the truck started and it wouldn't go faster than 30 mph and as soon as they stopped and turned off the engine it wouldn't start again. I came to the truck 2-3 hours later and it started right up and ran perfectly.When it decides to run well it sounds perfect. Does anyone have any ideas that might help me?

mudseeker · 08-24-2008, 12:03 PM

i had to replace the ignition switch in my '97 truck because the speedo was jumping around to 80 and back while i was going through town. within a few miles, the speedo died and i lost first gear and overdrive.

leolkfrm · 08-24-2008, 02:06 PM

put a scan tool on it and evaluate from there

Lariat · 08-24-2008, 04:57 PM

Thanks Guys,

I was thinking about getting a ProScan Universal and see what comes up. I dried up everything electrical near the engine, MAP Sensor, distributor, etc. Replaced the fuel filter and tested the pump at the same time. I feel it might be the sock in the gas tank.

08-24-2008, 11:04 AM	#1
Lariat Senior Member Join Date: Aug 2008 Location: West Palm Beach, Florida Posts: 85	GMC 3500 - starts when it wants & tranny crazy I have a 1999 GMC 3500 van w/ a 5.7L engine. My truck has been running fine but every now and then, and more so recently, it will start when it wants, cold or hot, and the transmission on one day is fine and another won't drive faster than 30 mph with a crazy speedometer that reads 55-110. I think it's linked for some reason. I replaced the fuel filter and the battery and it seemed to do the trick, but in two days someone borrowed it to go two miles, they got the truck started and it wouldn't go faster than 30 mph and as soon as they stopped and turned off the engine it wouldn't start again. I came to the truck 2-3 hours later and it started right up and ran perfectly.When it decides to run well it sounds perfect. Does anyone have any ideas that might help me?

08-24-2008, 12:03 PM	#2
mudseeker Moderator Join Date: Feb 2006 Location: michigan Posts: 3,933	i had to replace the ignition switch in my '97 truck because the speedo was jumping around to 80 and back while i was going through town. within a few miles, the speedo died and i lost first gear and overdrive. __________________ member map add yourself

08-24-2008, 02:06 PM	#3
leolkfrm Senior Member Join Date: Mar 2008 Location: N.Y. Posts: 951	put a scan tool on it and evaluate from there __________________ 4 wheels move the body 2 wheels move the soul

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08-24-2008, 04:57 PM	#4
Lariat Senior Member Join Date: Aug 2008 Location: West Palm Beach, Florida Posts: 85	Thanks Guys, I was thinking about getting a ProScan Universal and see what comes up. I dried up everything electrical near the engine, MAP Sensor, distributor, etc. Replaced the fuel filter and tested the pump at the same time. I feel it might be the sock in the gas tank.