(94 full size blazer) engine rpm going up and down around 55mph

[crashland73]

I have a 1994 full size 4x4 2dr blazer and the engine is running odd. While driving normaly down the road around 55mph or so, you can watch the tach and it will start to vary about 100 or so both ways. Here is a list of what I can remeber that I replaced;
EGR valve
EGR silinoid
Destributor,cap,wires,plugs ect.
Timed it, retimed it, and so on many more times
Oxy. sensor
Hoses (all)
Throttle body gasket
Fuel filter
Air filter


I think thats it. I havent been able to check the fuel pressure. I can hear the fuel pump work, it seems like it takes forever for it to shut off. I have noticed that. Compared to other vehichles that I have had like this one. I was wondering if it might be the throttle possition sensor or maybee the fuel pickup hose in the tank. I dont know. Also, it just seems to have good days and bad days. Some days it runs GREAT and others, well, I want to throw a grenade under the hood and run!

[dave]

Without a data log, it's not going to be easy to figure out what is happening. I use DataMaster freeware software from TTS Power Systems

The DataMaster data log will show what the TPS is doing, along with everything else sensor wise.

dave

[crashland73]

im asking this out of pure stupidity,whats a data log? and where do i get one?

[dave]

"pure stupidity" I don't think so.

The ECM provides information about how the engine is running. To read the information in the ECM, a special tool is used called an ALDL cable ALDL OBD1 OBD cable OBDI OBD2 engine codes

One end of the ALDL cable is connected to the pickup ALDL connector, the other end of the ALDL cable is connected to a Laptop computer.

The Laptop computer needs software to read the ALDA data stream of information, available from TTS Power Systems

I admit to figure out all this Data Logging stuff can be a huge headache!

I paid a couple hundred bucks for my Laptop and about $60 for the ALDL cable. I used the DataMaster freeware software for a short while, then paid $119 for the unlimited use DataMaster software.

I sure as heck can't afford the "special tools" used by GM mechanics or the "special tools" sold by Snap-On or Mac Tools So I figured out how to use the "Poor Mans" special tools. I've saved so much time and money using my "Poor Mans" special tools ... I can afford to go to Hooters for lunch!

[classjoe]

sounds to me like its a torque converter locking /unlocking , you dont drive with the foot on the brake pedal do you?? one way to test is to drive say 55 and just barely tap the brake pedal enough to enact the brake light but not enough to get the brake pads to make any contact the converter should unlock and your rpms should increase about 300 rpm. let go and your converter should lock up again rpms should go back to normal.

[crashland73]

i will check. its down right now. my brother is putting all 4 balljoints in it.that is a JOB! i dont drive with my foot on the brake. could it or something be making it slip? something electrical?

[crashland73]

i checked it out last night and it worked, i tapped the brake and it went up in rpm. then it shifted back into overdrive or whatever. i am wondering if it might be the throttle possition sensor or even the ecm.
I did one time, leave the ecm check key in the slot and started it up, i shut it off as soon as i realized what i did. it ran real wierd, but i pulled it out and restarted it and it appeared fine. I hope it isnt it. Oh, this is off the subject, is there any way that I can override the speed shutoff? It shuts off at about 95 or 100mph and I dont want that. I know I dont run that speed much but, I still dont like it that way.

[dave]

Originally Posted by crashland73

i checked it out last night and it worked, i tapped the brake and it went up in rpm. then it shifted back into overdrive or whatever. i am wondering if it might be the throttle possition sensor or even the ecm.
I did one time, leave the ecm check key in the slot and started it up, i shut it off as soon as i realized what i did. it ran real wierd, but i pulled it out and restarted it and it appeared fine. I hope it isnt it. Oh, this is off the subject, is there any way that I can override the speed shutoff? It shuts off at about 95 or 100mph and I dont want that. I know I dont run that speed much but, I still dont like it that way.

Leaving the ECM check key in should not create a problem.

To override the speed setting, changing the PROM code is required. The PROM code can also change the transmission shifting. I attached a screen shot of some of the stuff that is programmed into a PROM

dave

[crashland73]

where do i go to get this done?

[dave]

Maybe you can get Sinister Performance, LLC. to provide you with a custom chip? I really don't know who to recommend for a custom PROM, I do my own custom PROM chip programming.

dave