98 Bravada Tranny problem... maybe

[GNXfan]

I have a 98 model with 112,000 miles on the clock. I just took it on a long road trip, 800 miles, without any problems. Then after I get off the freeway in my destination city I get caught in heavy stop and go traffic. After the third stop at a redlight it starts to shift from first to second gear and just dies completely. It died very abruptly almost as if I turned off the ignition switch. I let it rest for about a minute and it started right up. Started off again and it did the same thing. Next I tried babying it by slowly taking off and it seemed to help for a few more take offs but then started doing it again. I finally made it to the hotel where it sat for two hours. Then I drove it again for maybe 1+1/2 hours and it started shutting down again as before.
Next day I got back on the road for my return trip and it ran fine about the first 100 miles and then shut down again except at 65mph.
I have worked on this tranny before by installing a Transgo kit made to eliminate the 1-2 hard upshifts and all of the other pesky problems with this tranny as well as a new filter and fluid change. I also have changed the transfer case fluid with DexronIII fluid. The check engine light has never appeared during any of this. Any ideas as to what the problem might be??

[Chris Stewart]

Sounds like some of the ignition switch problems reported on the Blazer site.
Do the dash lights go out or the radio go dead too. Does the engine turn over good when you try to restart?

[GNXfan]

When it shuts down it is like total electrical failure for a few seconds then all of the dash lights come back on just like they when you first turn the key before starting. Then engine turns over good immediately after this happens but will not start. Sounds like it isn't getting enough fuel sort of. If you wait about a minute it will start right right up like nothing ever happened.
This only seems to happen when the operating temp of the truck is hot, never when it's cold.

[Chris Stewart]

Have you already cleaned your battery connections?

[GNXfan]

Yes, the battery terminals are clean with no corrosion.

[Chris Stewart]

I'm lost but for some of the more helpful guys...do you hear any click noises like a breaker is tripping or resetting?

[GNXfan]

No, no weird noises of any kind. I am going to re-clean the battery connections, have the battery load tested and check the ignition switch to see if I can spot any problems. I talked to a friend of mine who's a retired mechanic and he seems to agree with you that the ignition switch may be the problem. He said the contacts wear out over time and arc causing it to overheat which may be why it only dies out when hot.

[muddog321]

Lots of possibilities here - coil overheats as the ign module never totally shuts off voltage, crank sensor failing, fuel pump failing so check pressure, wiring has a short or loose connector, but the only Blazer that has a known ign switch problem is the 97.

[GNXfan]

Well the fuel pump/sending has been replaced about two months ago with a brand new Delco unit because the gas guage read full all the time. As far as the crank sensor I did have a similar problem with my 87 Grand National so that's a possibility. I had the battery checked and load tested, it's OK. Cleaned terminals. So I guess I should I should focus on the ignition module, coil or the crank sensor? Please advise as I have puchased a new Delco ignition switch and don't want to install it if it's not needed. Thanks in advance.

[Blue Bowtie]

Not directly related, but once you get teh problem at hand resolved, you may want to check the transfer case. If it's a NPG case, you probably don't want to run Dexron III in it. AutoTrak II is the recommended oil.

[GNXfan]

Well today I finally started checking things and started with the Crank Sensor and according to my Haynes manual it is probably bad. The manual said it should ohm out between 800-1,200 ohms and it tested out at 1,581 the first time I checked it. I tried it again and it wouldn't read anything at all so I lightly tapped it on my work bench and then it read 1,900 ohms! Does anyone here think that may be my problem?

[GNXfan]

Since last post I have had the ignition module checked at 4 different parts stores on their test benches. O'Reilly(1)said it was bad, Autozone said it was good, Advance never could find the right connectors to hook it up to the tester so the dude just got out his VOM at siad it was good, lastly went to another O'Reilly and he said it was good. Majority says it's good. I have only driven the truck for short 20-30 mile jaunts since the big stalling incident a few weeks ago and, of course, it's running fine since I'm not 800 miles from home. I'm still debating changing the ignition switch since most people say it's the 97 models that had that problem, not the 98 models. The family basically doesn't trust taking it far from home.

[Chris Stewart]

Originally Posted by GNXfan

Well today I finally started checking things and started with the Crank Sensor and according to my Haynes manual it is probably bad. The manual said it should ohm out between 800-1,200 ohms and it tested out at 1,581 the first time I checked it. I tried it again and it wouldn't read anything at all so I lightly tapped it on my work bench and then it read 1,900 ohms! Does anyone here think that may be my problem?

Do you think it made a better connection to the DVOM when you tapped it?

[GNXfan]

Chris, I'm not quite sure what you mean. I have already changed the crank sensor out with a new one. I've haven't really driven the truck for long trips yet to really see if that solved the problem or not.

[Chris Stewart]

Sometimes the alligator clips on mine don't make a very good initial connection but wiggling the alligator clips helps make a better connection as would bumping or jarring the connectors.
Any improvements the last coupla days?