1996 blazer-stalls, run rough, check engine light

[boolander]

3 months ago, fuel pump goes. i replace it along with the tank. 2 months ago, check engine light comes on (mass air flow malfunction, trans. control malfunction). i clean the maf and everything is fine. 2 weeks later, blazer constantly stalls and check engine light comes on (throttle position sensor, trans. control malfunction). i replace the tps, and everything is fine. 2 weeks after that, engine runs very rough, can't go more than 15 mph without stalling, engine light comes on (manifold air pressure sensor, trans. control malfunction). i replace the map and everything runs great. now, the engine is running rough again, stalls every 10 minutes, engine light is coming on and i'm getting various codes of maf malfunction, map low input, tps low input.
Anyone else having similar problems? Anyone have solutions? This whole thing is driving me nuts!

[MT-2500]

Welcome to AF
What are the code no?
Have you checked the EGR valve for a carbon ball stuck in it?

[boolander]

Originally Posted by MT-2500

Welcome to AF
What are the code no?
Have you checked the EGR valve for a carbon ball stuck in it?

thanks for your reply MT-2500.
i did pull the egr valve, and it looks ok. no code numbers, i'm using a reader that spells it out. i've been getting spuratic readings over the last couple of days, from"air pressure" to "mass airflow sensors" to "idle air control valve" but they've all gone and stayed gone after clearing the codes. the latest errors has been on a while, and i can't clear it out. they are "throttle/pedal position sensor switch A curcuit low input" and "transmission control system malfunction". i did replace the throttle sensor a couple months ago (along with the air pressure sensor). idle is rough, wants to stall after letting go of throttle and/or will not go above 20 mph.

[old_master]

Did you check for vacuum leaks around the intake manifold?

[boolander]

Originally Posted by old_master

Did you check for vacuum leaks around the intake manifold?

i have not. where would i check for them (hoses, air leaks in gaskets, etc.)?

[Sparky1349]

Originally Posted by boolander

i have not. where would i check for them (hoses, air leaks in gaskets, etc.)?

The easiest way to check for vacuum leaks is to get a can of Carb Cleaner and start spraying it around areas where there may be vacuum leaks like the base of the throttle body, along intake manifold gasket, EGR valve, etc..... If the idle changes (gets smoother or speeds up) then there is a leak in that area. You might want leave the air cleaner on to prevent any confusion over whether there is a vacuum leak or the carb cleaner is innocently getting sucked into the throttle body, in addition block off the PCV valve hose and vacuum line to the power brake booster to rule those 2 areas out.

The other thing that you might want to check is the fuel pressure since the symptons you describe sound like it's not getting enough fuel, I know you replaced the pump and the tank but that doesn't mean that the new pump isn't operating correctly or was misinstalled. In addition the replacement of the pump could have shook some crud loose that is stuck in the fuel pressure regulator. I don't know for sure but I think the specs, for this engine is 52 psi absolute minimum and 60 psi is highly desirable, Anybody out there have an opinion about the correct fuel pressure?

Those 2 items should keep you busy for a little while, let us know what you find.

Sparky

[boolander]

thanks for all the info everyone. i've played around with a few things, but frustration has got the better of me, so i dropped it off at my local chevy dealer. i'll post the results when i find out what's up...

[boolander]

dealer called to let me know that the fuel tank pressure sensor was bad (which i replaced along with the entire fuel pump assembly a little while ago), it was dropping the voltage of the entire curcuit to 1 volt instead of the needed 5 and that is why i was getting random errors on all the emmision sensors. does this sound correct to anyone? could the wiring harness going to the sensor be bad, or could there be a short somewhere else? anyway, the dealer calls me back about 20 minutes after telling me this to let me know that they had broken the connectors on top of the fuel pump assembly while taking the connectors and hoses off and it will cost another $300 to fix that as well. i tell them that the fuel pump assembly is only 3 months old and i'm not paying for something they broke. after some back and forth they said they will handle it, and that's what's up with this mess for now. i will put up another post when i get the blazer back.

[boolander]

got my blazer back from the dealer, and so far, so good. still idles a little "rough" but no light and no stalling, so far. dealership ended up replacing the fuel tank pressure sensor, and replacing the fuel pump assembly they broke (for free). if this problem comes back, i will post, and thanks again to all who offered help.

[old_master]

It was good of them to replace the fuel pump module, being they broke it, but, the pressure sensor is part of the fuel pump module. Anyway, glad you got her going again.