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97 chevy truck starting issue.

R

Rebil79

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I posted about this truck (97 chevy 4x4 3500 pickup 5.7 auto)a while ago but here is the jist of the issue.
Ok so last spring or so the truck would start and stall sometimes running for several minutes, sometimes seconds. Then got to the point that it basically wouldnt start. Did all kinds of tests, low fuel pressure, so changet the pump and filter, fixed a fuel leak still no differnce. Put is on a Gm scan tool came up with bad crank sensor. Replaced, thought it fixed it a couple days later same thing. Turned out to be a bad sensor (found out through testing it) replaced again still same issue. Replace cap, checked for play in the distrubtor all seem good. So with the computer and my brother who is a mechanic we think we have tested everything and he was thinking bad ecm.
So come mid winter the truck just started to act normal. I was able to plow with it and would start everytime. All spring and summer any time I would try to start it, it would start and run just fine. I would let run for 15 min or so, shut off start up a couple times all good.
Now, Im giving the truck to my other brother so he can plow with it, started doin the same thing again. Start then stall.
So, Im not sure if I should just try and get a used ecm or if there is something else to check. Last time we had the computer on it there wasnt any codes or anything.

Any ideas?

Sorry to be so long but this is really starting to piss me off. I have put to much time and money into this stupid thing.

Thanks
 
96-2000 vortec's had dist cap moisture problems . also worn dist gear problems and even seen few were teeth ground off the gear for the dist.

if you pull the dist you need a scanner to set timming .

i put 3 cap's and rotors on my old 96 in 14 month time.
 
sweetk30 said:
96-2000 vortec's had dist cap moisture problems . also worn dist gear problems and even seen few were teeth ground off the gear for the dist.

if you pull the dist you need a scanner to set timming .

i put 3 cap's and rotors on my old 96 in 14 month time.
Click to expand...


Its got a new (when I first started messing with this) cap and rotor.
I havent pulled it, I did check for play and didnt seem to be much.

Not sure why it acted fine all summer long though.

Might be worth another cap and rotor becaus we did get a lot of rain from Sandy and it is very frosty/dewy this time of year so maybe it is moisture?


Rebil
 
I should also tell ya that when it does run, it runs smooth, no skipping, or roughness. Will idle basically perfect, and when it stalls its like you turned it off with the key.


Rebil
 
check ignition switch.

In your first post you said low fuel pressure, and a new pump did not fix this. Did I understand this correctly?
 
black dawg said:
check ignition switch.

In your first post you said low fuel pressure, and a new pump did not fix this. Did I understand this correctly?
Click to expand...

New fuel pump fixed the pressure issue, not the starting issue.


Rebil
 
Ok, still not fixed. Put in a new distributor (a complete distibutor with new cap and button) and getting the same results. Now when it dosent start Im getting no spark either. With the scan tool on it, its setting the same two crank sensor codes. The scan tool is gettin no reading from the crank sensor. When it does start the crank sensor readings are what they are supposed to be.
Last year when we tested the crank sensor duty cycle (back probing at the ecm) the numbers where half of what they should be when not starting. Replaced the crank sensor at that time and it seemed to fix it for a short time.

So now we are thinking maybe the ecm?? Im gonna grab an ecm from my brothers truck to plug in and see if it starts before I just buy an ecm. Im tired of throwing money at this thing.
Any other ideas?

Rebil
 
63chevyll said:
Have you tried shiming the crank sensor? Or just a used sensor ?
Click to expand...

never shimed. Just replaced with a new one after the intial crank sensor code about a year or so ago. Seemed to fix the problem, I did it at my fathers house so everytime I went over I would start it and let it run for 10 min or so. Did this several times, drove it home and next time I went to start it nothing. Came back with the same two crank sensor codes, so we back probed at the ecm and run a duty cycle test and recorded the numbers and did the same thing on a truck that was running. It had half the numbers off the good one. We then checked the wires from the ecm to the sensor and all checked out fine. Put another new sensor in and seemed to fix it again. Shortly it started acting up again. Then all summer it started just fine untill I went to drop it off at my brothers house a month of so ago.
So yesterday we did the distributor and nothing changed. We checked the wires again to the sensor and all checked out fine. Dosent seem to be any bad wires or connections anywhere.
Cant imagine I got two bad crank sensors but...

Rebil
 
A long time ago, I corresponded with a service rep trying to fix an intermittent skip in a Volkswagen Rabbit.
Car was brand new, still on the dealer lot.

Kept seeing odd output from the crank sensor on the flywheel. New sensor did not help.

Finally the factory was going to just have it shipped back and parted out, but som factory reps came by before they made that decision for sure.
They took an interest, and extended their stay.

I don't remember now, if it was a flawed casting or just a burr, but the mount that the crank sensor was mounted on had a problem.
The distance was right, but the angle was wrong. It was not obvious, but it was sitting at an angle, which affected the signal it was producing.

Those things really need to be at right angles to what they are reading so as to get nice sharp waveforms.

You might check to see if its square.
 
I just went through his.... Got a 99 burban for parts..... No start... They changed the crank sensor a few times.... I took a good used factory sensor and put in it.... Started right up..... Most of the aftermarket sensors are junk..... Every one that I know that runs and aftermarket sensor has had problems..... Gpo to the junkyard and try to find a good used one..... You can look at the S10's to they use the same sensor sarting around 93 or so in he first gen vortecs...
 
bronc3buster842001 said:
I just went through his.... Got a 99 burban for parts..... No start... They changed the crank sensor a few times.... I took a good used factory sensor and put in it.... Started right up..... Most of the aftermarket sensors are junk..... Every one that I know that runs and aftermarket sensor has had problems..... Gpo to the junkyard and try to find a good used one..... You can look at the S10's to they use the same sensor sarting around 93 or so in he first gen vortecs...
Click to expand...


Could have used you a lot earlier. Just figured this out. Took a factory crank sensor out of my brothers truck and it started up just fine. Goin to get a gm one from a dealer tomorrow. Went through two new aftermarket ones.
Anyone have any idea what a new sensor from the dealer is gonna run??

Rebil
 
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