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97 Blazer shuts off while driving


htsob
12-12-2004, 12:36 AM
Ok folks, it has been a furstrating month and now I am back with the same problem. I now this is looooonnnnnng, but I am about to take this truck for a long drive on a short pier, ha, if it will let me....so any help would be greatly appreciated.

My 97 Blazer continues to just shut down while I am driving down the road and sometimes it won't start after being driven, then parked for awhile, then just won't start. This has been going on for a few months now. I starting reading this forum a few months ago and have tried all the fixes you guys have come up with and I am right back where I started. I started by replacing the ignition switch harness ($133.21) and the truck worked fine for about a month. The truck broke down again, had it towed home and did some more research. All indications lead to fuel pump not working, since I already did the ignition switch. No sound from pump when key on, truck felt gas starved and not much fuel pressure when I pressed on the fuel rail shreader valve. So I dropped the tank and replaced the fuel pump/sending unit (AC Delco #MU112 $370.38) and fuel filter ($19.95). I checked the old fuel pump sending unit per my Haynes manual and it was bad so I hoped when the new fuel pump module was installed it would fix my dash fuel gage. No such luck. After I replaced the pump, filter and re-installed the tank, everthing seemed to be working fine. Truck ran another two weeks and then shut down again while going down the road. Towed it home again, AAA loves me. More research, more parts (Fuel relay $27.50, Oil Pressure switch $48.50, New Battery $95.00). Tried the pressure switch as they say this my cause the fuel pump to shut off if the oil pressure drops to low and just tried the relay out of desperation. Once again, after I was done, truck started right up, ran fine for awhile and then shut off while driving down the road tonight. I tried a few things when it broke down this time. Tried adjusting the steering wheel, wiggiling the wires under the dash around the column in case the new ignition harness was bad, no luck. However I decided to check the fuse in the power/aux slot #9 to see if it had blown but it was fine (per my schemetic, this fuse controls the fuel pump). When I put the fuse back in and tried the key the truck started right up. On the rest of my way home the truck shut down three more times at different intervals. Each time I just pulled the same fuse, waited a couple of minutes, put it back in and the truck started right up. So without spending too much more time and money is there anything left to try? Is there some monitor module or brain module that my be causing the truck to shut off which is the reset when the fuse is pulled? Why does it re-start and wrong like nothing is wrong just by pulling and re-installing the fuse? Help please, this truck has seen more driveway time then road time since I bought it used with 98000 mi. less then a year ago.

blazing
12-12-2004, 06:45 PM
http://www.automotivehelper.com/topic67530.htm
might be of some help, others face the same problem

barpat96
12-13-2004, 08:38 PM
it sounds like the typical 97 blazer problem Ignition switch. I see that you already replaced that and it worked fine for a month then started again. I don't know if the new switch is improved from the original. I had the same symptoms you have. I didn't replace mine, instead i cleaned off the contacts which had carbon buildup on them. about a year later it got buildup on it again, this time causing tranny codes to come up, so i cleaned it again and it has been working fine. So it is possible to get the same problems again unless they have solved the cause of the carbon.

Good luck,

htsob
12-13-2004, 10:53 PM
Thanks for the responses. I will try another look at all the electrical circuits in the area under the dash and on the columnm to see what I might find. Still not sure why the truck restarts every time by just removing and re-installing the #9 fuse.

htsob
12-21-2004, 10:58 PM
Thought I would just post an update on my 97 blazer problem. Disassembled the whole dash and checked all wiring connections and found nothing indicating a problem (no shorts, broken wires,loose connectors). Removed the ignition switch and disassembled it. Only thing looking suspect were the contacts, so I cleaned them up and put everything back together and the blazer started right up. We will have to wait and see how long it goes this time before it shuts down while I am going down the road.

BlazerLT
12-22-2004, 04:54 AM
Ok, good, I thought it would be the switch.

I would replace it if you have the money.

barpat96
12-23-2004, 12:13 AM
yeah i suggest replacing it too. i had the same problem you did. I also cleaned the contacts and drove it until a year later when i started having "tranny Problems" it turned out the switch again

BlazerLT
12-23-2004, 12:37 AM
yeah i suggest replacing it too. i had the same problem you did. I also cleaned the contacts and drove it until a year later when i started having "tranny Problems" it turned out the switch again

Thanks for chiming in.

Good to see someone with experience in this matter lending support.

htsob
12-23-2004, 01:05 AM
Ok in case I haven't mentioned it already, this is a new switch/harness purchased and installed in August. When I had the dash all apart I also completely disassembled the switch and thoroughly checked it out. Checked continuity through all wires and contacts, checked for broken wires or loose contact at connector terminals, checked all solder joints, disassembled springs and contacts (this is where I found the carbon buildup although it was very light and only on two of the contacts) and found the switch to be working fine. Now for the best part, as I mentioned yesterday, the truck started up and ran fine after everything was put back together until today. It died on me going down the road at 30mph. Same exact thing it has been doing. And as I mentioned before, I remove the 20amp fuse in the #9 position on the fuse box, wait about 30 sec. and put it back in and the truck starts right up and off I go. I know you guys all keep saying the switch is bad but why would the switch repair itself when I remove the fuse? The #9 fuse is called ECM Battery and feeds the Fuel Pump Oil Pressure Switch (just replaced), the Fuel Pump Relay (also new) and the Powertrain Control Module (PCM). I'm leaning toward it being a problem in the PCM. The fact that the truck strats up and runs fine after removing and replacing the fuse leads me to believe that by interrupting the power flow to the PCM, it resets itself and runs for awhile until whatever is causing the problem trips it off again. Any thoughts on this theory?

BlazerLT
12-23-2004, 09:37 PM
Is it a new switch or just a switch you cleaned in August?

The switch controls pretty well everything and even can cause transmission problems. It is the leading cause of 1997 failures and by the sounds of it, it is your problem too.

igotjunk
12-24-2004, 05:25 PM
ok, this is my first time on this site sorry if its messed up.. you said that when you pull the #9 fuse and wait then replace it, the blazer starts right up.. well for sh!ts and giggles try cleaning the connection there, maybe through driving the fuse moves enough to lose the connection (considering there is dirt or corrosion). what can it hurt?

BlazerLT
12-24-2004, 05:56 PM
Again, I will ask, was it a new switch in August or did you just clean the existing one?

htsob
12-26-2004, 10:30 PM
Again, I will ask, was it a new switch in August or did you just clean the existing one?


Switch was brand new in August.

In response to the fuse contacts, I didn't mention before that I had to completly replace the fuse block itself and at that time I cleaned and even replaced a few contacts. So I am confident in having good contact between the #9 fuse and associated wires.

I had a chance to talk with my brother in-law (GM Smog and Tune-Up Mechanic) over Christmas about this and he said there was a repair bulletin put out by GM on this switch problem. He said it mentioned something about replacing some of the wires in the switch harness or something like that so you wouldn't have to keep putting in a new harness. He is going to get me a copy of the bulletin next week. He also thinks it is the switch and even though I just replaced it with a new one it might be bad. He said the continuity check could be misleading. He didn't think the PCM would be bad and thought that the fuse remove and replace and then the truck starts is just a coincedence. I will see what the bulletin has to say. I will post the contents of the bulletin as soon as I get it, it may help someone else out. He did give me a couple of other things to try next time it shuts off, so Im will see what happens in the next few days.

stanwood
12-26-2004, 10:51 PM
Just a wag here. But my 4WD was intemittent and I took it in to for repairs and they found the big electrical plug bolted to the firewall was loose. I thougt it might be worth a shot if it was loose enough to cause your electrical connection to act goofy.

Ok folks, it has been a furstrating month and now I am back with the same problem. I now this is looooonnnnnng, but I am about to take this truck for a long drive on a short pier, ha, if it will let me....so any help would be greatly appreciated.

My 97 Blazer continues to just shut down while I am driving down the road and sometimes it won't start after being driven, then parked for awhile, then just won't start. This has been going on for a few months now. I starting reading this forum a few months ago and have tried all the fixes you guys have come up with and I am right back where I started. I started by replacing the ignition switch harness ($133.21) and the truck worked fine for about a month. The truck broke down again, had it towed home and did some more research. All indications lead to fuel pump not working, since I already did the ignition switch. No sound from pump when key on, truck felt gas starved and not much fuel pressure when I pressed on the fuel rail shreader valve. So I dropped the tank and replaced the fuel pump/sending unit (AC Delco #MU112 $370.38) and fuel filter ($19.95). I checked the old fuel pump sending unit per my Haynes manual and it was bad so I hoped when the new fuel pump module was installed it would fix my dash fuel gage. No such luck. After I replaced the pump, filter and re-installed the tank, everthing seemed to be working fine. Truck ran another two weeks and then shut down again while going down the road. Towed it home again, AAA loves me. More research, more parts (Fuel relay $27.50, Oil Pressure switch $48.50, New Battery $95.00). Tried the pressure switch as they say this my cause the fuel pump to shut off if the oil pressure drops to low and just tried the relay out of desperation. Once again, after I was done, truck started right up, ran fine for awhile and then shut off while driving down the road tonight. I tried a few things when it broke down this time. Tried adjusting the steering wheel, wiggiling the wires under the dash around the column in case the new ignition harness was bad, no luck. However I decided to check the fuse in the power/aux slot #9 to see if it had blown but it was fine (per my schemetic, this fuse controls the fuel pump). When I put the fuse back in and tried the key the truck started right up. On the rest of my way home the truck shut down three more times at different intervals. Each time I just pulled the same fuse, waited a couple of minutes, put it back in and the truck started right up. So without spending too much more time and money is there anything left to try? Is there some monitor module or brain module that my be causing the truck to shut off which is the reset when the fuse is pulled? Why does it re-start and wrong like nothing is wrong just by pulling and re-installing the fuse? Help please, this truck has seen more driveway time then road time since I bought it used with 98000 mi. less then a year ago.

igotjunk
12-28-2004, 09:15 PM
i had the exact same problem you have or had... it was the fuel pressure regulator, i baught the replacement at advance auto and a gasket kit because you have to take the top of the intake off to replace it. anyways i think its you best bet, if you haven't already tried it.

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