Alright, recently I was having trouble with the 4-wheel drive. I traced down the culprit to the 4wd actuator under the battery. It is getting vaccuum at the wrong time. So I simply just unhooked the vac line from it until I get a chance to work on that problem.

It's not even been a week yet, or maybe it right at a week, and I'm already on to something new. Sort of.

It's an old problem I thought had went away, but it's reappearing now. It's something that happened when I first got the blazer, then went away, then came back, then went away. Apparently is a cycle of coming and going. It always seems to dissapear again before I trace down whats going on.

I have a 5-speed, so I have that stupid shift light. Lately when the shift light comes on, the engine momentarily cuts out completely. Just for a second, maybe not even a whole second. It cuts out hard though, like it loses electricity to the spark plugs or something, but I'm unsure. The guages never do anything funny when it happens, and since I know when the shift light comes on I can make the problem occur over and over again. That is until I turn it off, then back on again, and then it's usually ok for a little bit. There really are no preceding symptoms to it. Just one time I'll get in it and take off and it acts like a piece of junk.

What is happening when the shift light comes on? What all is going on that would make it cut out so hard like that? It makes the whole truck jerk hard. I can't figure that one out for anything.

List of what's recently been changed
Fuel Pump (Less than six months ago)
Distributor Cap/Rotor Button/Plug Wires/Plugs (with last fuel pump @ less than six months ago)
Radiator (Two Months ago or so)
Transfer Case Switch (Two weeks ago)
4wd actuator (Two weeks ago)

I don't believe any of that will help, since the problem occured both before and after the changes. Since day one when I got the blazer, and so far no one has been able to help. I hope that one of you will be able to.

 

Does it cut out at a certain rpm, or is at the exact time the shift light comes on?

 

just a thought..... try tapping the computer with the handle of a screwdiver, not so hard that you dent it , just a light tap. I know they have in the past had problems with cracked circuit boards. There would be no problem then you hit a bump or the thing reaches the right temperature and the engine would die. As it cooled down the circuit would make contact again and no more problem...for a while. Also because the circuit was temporarily broken in the computer, there was no code stored.
That was most common in the older Chevy Citations and Pontiac 6000.
Like I said ...just a thought

 

Your 4WD Actuator problem maybe the new switch you had installed, I believe that it has 3 vacuum lines on the switch and they can be rotated accidently and cause this problem. I had a friend who had the switch replaced at a local tranny shop and that is exactly what happened to him, once they realigned the hoses on the switch on the transfer case all was well with the Actuator.

 

I've been doing a little reading about this and I see it's the PCM that controls the shift light. It also controls the IAC and can shut down injectors if it thinks the engine is over revving. I still don't have an actual answer for you, although I figure the problem might be in the PCM or loose or poor electrical connections.
What year is your truck?

 

Just the exact time the shift light comes on. Which can be over a range of RPM's depending on the driving situation at the moment.

 

It is a 2001 model.

I have given some though to it maybe being the computer. I figure it would only do it if it had a reason to though. It's like a cause/effect, and the effect doesn't give enough information for long enough to find the cause. The randomness of it is what gets me. It might do it right now if I got in it, but then again, it might not do it for a month, or six months, or a couple days, who knows.

 

The shift light problem could be related to a bunch of different scenarios. It could be a bad crank sensor, throttle position sensor, Intake Air Control sensor, bad connnections in the wiring harness or a frayed wire (wires have a certain amount of resistance in them and when they go bad internally it can be a nightmare to find one), corrosion in a connection (not making good contact causing high resistance). There are a lot of things to take into consideration, so carry a notepad with you and write down all that was going on at time of the problem and what led up to it, then you could take it to the dealer and see if it is under warranty (TSB). Simple fix might be a reflash of the PCM with an update it to fix this problem...

Good luck and post up about the Acuator fix too....

 

This thing is giving me a nervous twitch.

Pretty much as I predicted, it didn't even think of doing it today. It's untelling when it will happen again, maybe tommorow, maybe next week. I just know I don't like when it happens.

 

That's the kind of problem that makes mechanics pull their hair out. Intermittents, uhg!
It's gotta be a bad electrical connection, but that's not my strong area.

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