I have an 89 4.3L tbi, it is blowin a little black higher in the RPMs, also it seems not to have the throttle responsiveness it should, this motor has only 35k on it since a full rebuild (heads done,bored pistons rings the whole nine) I have ran two diffrent sets of injectors, same problem. I am not sure what sensor/sensors to look at, it has a new exhaust (last night) and a good O2 as well, were should I look TBI guy

which codes are showing up? my first guess would be to check the t state and see if it is stuck open. that will make the motor think its cold and richen the mixture till it gets to operating temp.

by t state do you mean like the idle air control valve? I am not sure what t state is, I do have a new IAC on it also though.

I'm sure what t-state is either but typically a bad temperature sender will cause a tbi motor to run hot. Not the gauge sending unit, the one for the computor. I've had several go bad on my 4 cyl s-10. It also usually makes it want to run faster like in cold start as well though. Just a suggestion. Jake

Originally posted by inphobic
I'm sure what t-state is either but typically a bad temperature sender will cause a tbi motor to run hot. Not the gauge sending unit, the one for the computor. I've had several go bad on my 4 cyl s-10. It also usually makes it want to run faster like in cold start as well though. Just a suggestion. Jake

that kinda sounds right, mine seems to idle real high at start up, then as it gets to temp, after a trip down the highway or what ever, itll idle real low, like almost die low,also seems to always want to run at 200 on the crap digital guage(I also just put in a new radiator last week, temp is the same) were is the one for the engine, is it like a ported vacuum switch deal on the intake, or am I thinkin in the wrong ? Thanks for your help guys, good to get other opinions!! inphovic you goin to Disney next weekend? 7,8,9th?

local parts store has the temp sender on the shelf, its only like 7 bucks, and I dont have anything else to do on lunch, so I guess I will snag one of those, and give it a try, Im never scared to start with the little cheap stuff ya know!! ;)

by t state were you talkin about throttle postition sensor?

t-state = thermostat? :confused:

I did have a bad thermostat in a 4 liter that caused it to go rich.

-Matt

Yeah the sensor is located in the thermostat housing. Should be a 2 prong deal. I'm not sure that what your problem is with out seeing it though. Sounds like it could be a couple of different things.

Naw I wish I was going! Was down there last weekend. I've got a drag boat race in St. Louis so I can't make it. Where are you located in KS?

i was talking thermostat, if they hang open the motor runs cool and rich. but the temp sensor would also be a good spot to start. mike

A stuck fuel pressure reg can make them run rich.

Originally posted by inphobic
Yeah the sensor is located in the thermostat housing. Should be a 2 prong deal. I'm not sure that what your problem is with out seeing it though. Sounds like it could be a couple of different things.

Naw I wish I was going! Was down there last weekend. I've got a drag boat race in St. Louis so I can't make it. Where are you located in KS?

I live in Paola, work in Olathe, do you know Vernon Barfeild he drags boats, I work with him!!!!

My guess would be the temp sensor also. I had a 90 4.3 that I bought that had just been rebuilt and I took it apart to just check it out. Well I took the heads off and found out it was running rich and that ruined the oil so all the bearings were bad so take care of it or at least change your oil now while you look into it. The more I looked into the motor the more jacked it was from this one small thing.

MAP sensor can do that too. You should get a light from a bad MAP though. I say temp sensor or t-stat.

damn, I have the temp sensor here and goin to put it on tonight at the house, I cant believe that this sensor would throw the mixture off that much (if that is indeed what is doin it) thanks for the input, I did realize that the comp reads from the temp and O2, but, hell I dont know enough about it to say which one sensor ,map,temp,O2 would effect my mixture the way it is
Thanks again