Need Help A.s.a.p. Please!

lilblueskeeter · January 1, 2009

Ive searched the forum and have found some good info, but sadly it didnt help. My dad has a 2000 GMC sierra 4.3 that we cant get to start. For the last few months its had slight to moderate jumping and jerking when its wet or humid out. we've replaced almost every sensor and electronic part on it trying to fix it and have failed. A week ago my dad goes to start it and it just cranks and wont start, sometimes it tried to after releasing the key from start to run. sounded like it backfired thru the throttle body. Checked the fire, its good. Fuel pressure around 58-59. We reset the computer and it started and ran 5 or 6 different times for the rest of the day. The next morning the same prob. He replaced the ECM and now it cranks and starts but dies immediatly. replaced alot of stuff before this happened but since it happened we've replaced the coil, crankshaft pos sen, ECM, Fuel Press Reg, fuel filter, fuel pump (58-59 psi), had ICM tested (good), checked cap and rotor for moisture and problems, all looked good. We are running out of options and would really appreciate any advice possible. Sorry for the length but figured the more info i could give, the better you could help. If anyone would like the list of things we replaced prior to this not starting issue please let me know.

Thanks in advance, Danny.

pennzoil29 · January 1, 2009

Welcome aboard I see where you changed the crank sensor, did you try replacing the camshaft sensor? My 5.7 wouldn't start when it went bad.

lilblueskeeter · January 1, 2009

Welcome aboard I see where you changed the crank sensor, did you try replacing the camshaft sensor? My 5.7 wouldn't start when it went bad.

No we havent. The camshaft sensor and the ignition switch are one of the last few things the we havent tried yet but were planning to. Anybody know about the ignition switch, wether its a possibility or if this specific truck even has one? I only thought of this because i had a similar prob. with my mustang starting and stopping immediatly. ended up being my ign. switch. thanks for the info. Also is there any way to test or check the cam sensor?

88C1500 · January 2, 2009

Don't know if you got your truck running or not, but here's a few items that caused my 4.3 to die intermittently.

- Ignition Module, especially in warmer wheather as the components heated up. Could be sitting at a light and bang it would die. Might restart, or could take several minutes to restart. Would also intermittently lose several firings on the highway.

- Ignition switch, however I could sense/feel the sloppyness in the switch as I started the vehicle. If even got worse over time. Eventually after starting the vehicle, I'd need to hold the switch to the "on" position slightly to keep the engine running.

To troubleshoot I'd break it down between electronic and fuel. For example got fuel pressure at the rail? Good then check/listen if Fuel Injectors firing. Firing, then visibly look to see if fuel is spitting out of the fuel injectors.

Then perhaps put a timing light on the No 1 wire. See if it fires (consistently) while cranking. No firing, then backup from there.

lilblueskeeter · January 2, 2009

No we still havent got it running. we just replaced the ignition switch and we are fixing to replace the camshaft position sensor. The bad thing about it is its not an intermittent problem, it just all of a sudden one day it wouldnt start and we are still trying to get it started. anybody else have any ideas, anything at all? We're getting really desperate and impatient. Its really nerve wracking cuz we are almost out of options of things to replace.

Thanks, Danny

pennzoil29 · January 2, 2009

Sorry to hear that your truck is still down. Is the SES light on, have you scanned it for any codes? I just don't know. Keep us informed, and good luck.

lilblueskeeter · January 2, 2009

no the ses light is not on and we have scanned it for codes but since we have been messing with the electrical system so much we have had the battery unhooked about 15 different times so we have no codes. Is it possible to pick up codes even if it wont start and run? And if so how long would it take before it did?

pennzoil29 · January 2, 2009

no the ses light is not on and we have scanned it for codes but since we have been messing with the electrical system so much we have had the battery unhooked about 15 different times so we have no codes. Is it possible to pick up codes even if it wont start and run? And if so how long would it take before it did?

I can't answer that. I'm not a tech, I'm just going by my own experience on my suggestions. I really wish I had all the answer's. I alway's try to figure thing's out on my own first, but, sometimes I have to call up a mechanic buddy of mine for his input.

grampadirt · January 3, 2009

You might check out the oil pressure sensor and the wires going to it.My '95 just all of a sudden died going down a slight incline.Got to the bottom and cranked until the bat. was almost dead.I did some of the things you did and then with help from this website found out if the oil pressure sensor shows no pressure the ecm/pcm won't allow it to start.I found the sensor and sure enough one of the wires had laid against the exhaust man. & grounded out.I pulled it away from the man. turned the key and it started right up.I spent many hours and tons of $ just because of a grounded wire.Sometimes the simplest things can drive you crazy....

Atheist · January 6, 2009

I had a similiar issue. Sounds like you may have moved the rotor when replacing it. I did and was getting backfiring out the intake. Get the motor to tdc on cyl1 exhaust then set the rotor to the contact for that cyl and do a relearn if it starts,.

bobcat5544 · January 9, 2009

One of my fleet acounts their van has the exact same problem, I will be checking out this weekend once I find the problem I will let you know.

I have found 6 different post on the same van with the exact same problem but non of them have the answer.

If you found out what was wrong already PLEASE share.

Atheist · February 8, 2009

It ended up being a bad dizzy

lilblueskeeter · February 8, 2009

we finally got it fixed by doing a relearn, never noticed the security light. But now after working good for over a month we tried to start it this morning and again it just cranks but wont start. It acts like it tries to start as soon as i let off the key. so again we are stumped. Any help would be great. Thanks

lilblueskeeter · April 2, 2009

Well its been a while since we have had any problems, but just our luck it messed up again. This truck has broke down on us about 6 or 7 times and it will run ok for a while after we get it to run, but it will shoot a random misfire code. The check engine light will come on and normally go off on its own after a while. Ive never seen any vehicle that the light goes away on its own. is this normal? Also about a month ago we had to replace the battery and since then it hasnt missed, showed any codes or anything, It was running perfect, until 3 days ago we were driving down the road and it just died like u turned the ignition off and it would crank but it wouldnt start. The check engine light didnt come on either. We worked on it on the side of the road for about 2 hours (changed the cap, rotor, reset the computer) until we finally had to have it towed home. We are going to replace the dizzy tomorrow. But if that doesnt fix it we are at a loss. If anybody has any info that could be of any help we desperatly need it. Thanks

MikeInCtown · April 3, 2009

Before you just replace the dizzy, align it to the TDC by rotating the engine at the crank. The rotor should point at one of the terminals labeled with a number. Be careful as there are two timing marks on the 4.3 and you will need to align them correctly at the crank. See here for 4.3 dist info and pics about halfway down with alignment procedures.

The dist gears were plastic and would wear unevenly cauing rough running, misfires, and no start conditions. The new gearscan be had for $50 or so and a new dist with metal gears can be found on eBay. I'm betting that when you pull the dizzy that you find half the teeth are worn and half look pretty good. At this point it's about the only thing you haven't looked at.

One thing I didn't notice was if this happened in cool dry weather, wet weather, or any other specific conditions. I had horrible problems with aftermarket caps and rotors. Also had horrible problems with any wires from the big chains and finally a set of MSD wires solved most of my problems. (in the end my problem was most likely a bad injector assembly and FPR as those are notorius for causing problems too -got rid of the truck in Feb)