ok now i've got this thing running ok but i have a question about a cutting out problem im getting around 5000 rpm. i'm not sure what is going on but it doesn't really sound like the ignition. it starts shuttering really bad and doesn't like to go that high. so i am getting a MAT sensor code and a rich exhaust code. i replaced the mat sensor already and im still getting the same. i have datalogged it while driving and it is saying that the mat sensor is reading -40 degrees celcius. could this be related to it? it is a 1991 350 with a 510 520 lift with 230 236 duration cam, headers, msd 6al, new distributor, plugs, wires, cap, rotor. it has been rebuilt in the last 1000 miles also. any one ever heard of this? ideas? the weird thing is that it drives fine at lower rpms under 3500. i thought that the valve weren't adjusted right so i readjusted them and it helped a little bit.

 

anybody?

 

-40° C = as cold as it thinks it can go = the wire is unplugged somewhere; bad connection; etc. etc. etc. Basically the ECM can't see the sensor.

The "cutting out" problem sounds alot like valve springs. What springs did you put in it?

 

they are the ones reccomended by comp for the cam so they "should" be fine. thats what i was thinking also. ok my next question is could the ecm not seeing the mat sensor make it run like that?

 

just so everyone knows i had the heads assembled by a reputable machine shop in the area that cleaned them did a valve job and set the spring height to the specs for those springs.

 

This sounds like one thing that would make it enter "limp-home" mode. Check the wiring to the MAT and get the datalogger to see actual temp and I think you'll solve your problem.

 

ok so i got the datalogger on it yesterday and it still read -40 degrees Celcuis. like sofakingdom said that is as low as it goes which means the circuit is open. does the mat send a voltage signal i can measure with a volt meter? or should i just read it with a ohm meter. i checked the voltage at the mat sensor connector with the key in the on position but engine off and i got 5 volts. so is the problem in the sensor itself? even though it is new it could still be bad. i've had my share of those. (fuel pump and i was pissed).

 

The sensor is a variable resistor.

It should be many k when cold; a few hundred, maybe 1.something k, when at room temp; and down to a few hundred at underhood temps.

Make sure it's well grounded, if it's the 1-wire type. The open can just as easily be on the low side of the sensor, as on the ECM side.

 

yea thanks i'll look into the ground side as i followed the tan wire and it was good. hopefully that'll be the problem

 

ok guys it just got worse! i got the mat sensor fixed. it ended up being the connector not being tight on the sensor. not it is reading what it should be via the datalogger. after i reset the computer i took it for a little drive to see if it was still doing it and it was. i took a closer look at it while it was doing it and it happens more like 3500rpm and if you keep trying to push it further than 4000 it really doesn't like it. i'm starting to get worried now as i am trying to get it ready to sell. could anyone tell me what to look at or any ideas.