Here is my experience with the Coolant temp sensor... First I thought hey the PCM uses this sensor to turn on and off the fans right?? Righhhhhhhtt so I figure... whats the resistance of the sensor when the car is runing at 185*F?? with the aid of a Temp Meter and a DMM I ran the car to that temp... and measured the resistance at the end of the Temp Sensor leads... then I while still unplugged (the sensor) I measure the voltage across the leads... (the car off ofcourse) I then concected everything back up and ran the car till the fan came on, too readings of Resistance again...and voltage drop across the leads Then I calculated the resistance differential and got myself another Thermistor.. that I masterfully combined with a series of resistors and in parallel to the one in the car so when it reached 185 degrees... the combo was telling the PCM the car was atcually at 220*F degrees.. and gues what the PCM began turning the fans on and off at that temp...


It worked great when the car was warmed up... but as soon as it cooled overnight... the freaking thing would take forever to start and then barely get going untill it was warm again.. At that point I said to my self... Duh!!! the PCM is either adjustting fuel trim or Timing... I ran the car for three consecutive days and each time the car would cool off overnite and do the same problem again in the morning.... the last time.. the ambient temp was even cooler and I cranked her up... over and over and over....till the battery was just about dead when she fired-up ...... I turned her off... I removed the maligned (tumor like) resistor/Thermistor mod I had in parallel with my Coolant temp sensor... I went upstairs .. watched a movie then came back down.. check the engine block temp.. and it was only two degrees off ambient temp..... I cranked her up and WOW... she didnt even went half a turn and fired right up... Proplem solved!!! and she has never crancked past one turn and half when she fires up again.... see my point?? Do you still think its crazy??


I hope that explanation is clear enough... Now, what I have read from this people is that if the IAT (the other temp sensor) goes bad.. the car runs great when the outside temp is cool....but as soon as it get hot outside.. the cars take a crap... does that sound familiar??


So buddy here it is to you ....Does the Coolant Temp sensor affect the cars performance?... must defenetely... and so does the IAT sensor too but they both show the effects under diff conditions... I bet that if the Coolant sensor goes into either open or short circuit that car wont start for nothing...... ever again.. unless you replace the sensor..


Food for Thought....


Marvin out.

 

has anyone figured out this problem.cause mine does it when its cold,off the line it feels like its gonna die then theres a pop 9like alittle backfire)under the hood.then the car takes off.but major loss in power.use to be able to smoke the tires at the light now im lucky if they spin.hope someone knows what the problems is.cause this is really getting old.

 

My car was stumbling/surging/popping after it warmed up. Thought it was probably sensor on the fritz, so I hooked up to the laptop and watched it with pcmcomm. My left O2 was hovering around 0.5-0.6V. Swapped it out and the car is running great again. Glad I cured my stumble. I had a stumble just off idle last summer, but it hasn't returned thank god!

 

thanks for the advice

 

Well, all that talk and no one has done a full bonafide scan??? That sucks!! Where is everyone/anyone that has scanned it? Doesnt it cost like only $60 at the dealers??

I need some gritty techno from a scan. Someone, give me a good story that fixed your problem with a scan.

I do think that anyone that has lost power and has replaced just about everything should replace the timming chain. I had a 85 TBI 305 that would barely run. It would heat up bad and backfire left and right. I decided to sell it and wanted to clean up the engine. One of the things to keep the oil off the ground was to replace the timming cover crank seal. While I was there, I thought I would replace the very loose timming chain with a new one. I put it back together, fired it up and she purred like a kitten. Was a damn NICE car after that, for $99 !!! I even kept it around for 4 months and drove the **** out of it.

Anyways, I am gonna do the front works with mine and if I remember this post, I will chime back with some results. Last time I was in at 40k, the chain was loose as hell. I did not replace it at that time cause I didnt know if I was gonna keep the car. At 60k, I think I might as it has been a pretty good car after all.

 

I'm getting a full blown scanner tool this weekend from my mech (Snap-on tool, cost a few 1000 bux). I'm going to be doing every test i can think of to diagnose this low rpm stumble problem.. hopefully i'll find the problem. If i don't its off to the dealer I go...

 

so howd it go?

 

It's not quite the weekend yet This coming long weekend hopefully..

 

Hurry up, man!!!

 

Picking it up this sat at 12:30 PST Gona work on it over the weekend.. I just did the IAC pintle cleaning thing (took of the whole TB). Car runs much smoother now but i still had the slight chuggle/stumble happening around 2000 rpm on light accelleration. I'm so pissed at my car right now i'm gona try and scan every damn sensor on my car that i can find... wish me luck!

 

Do the 93's have IAT sensor???

 

Well I just done a search and stumbled across this thread. I have had the hesitation thing about as long as this thread been around. It seems to be worse the hotter and the longer I drive. It is only about 10 minutes to where I work. But I went about 80 miles Friday and I didn't think I was going to make it home. So I done the search to see if someone has found a cure yet. But alas after a year and a half it seems know one has found the cure or no one has posted it yet. I know this is getting long, but here me out. Has anyone pulled there intake out and cleaded all the carbon from the passages yet? The hesitation, backfire that sounds like a build up of carbon. The EGR valve only functions below about 2000 RPM where all our troubles are. Some of these posts are not the same problem we are having. I did notice a pattern though. All the cars that are doing this have over 80,000 miles. Since I need to fix my intake leak. Oil all over the front of the engine, opti , ect. I will take a stab at the intake, but before I do this, has anyoner tried this?
Just a shot in the dark from from someone who doesn't know any better.
John
P.S. 94 Z one of the few with a 105 MPH spedo A4 2.73 rear gears

 

I recently changed the EGR, same hesitation.

This is what I've done in the past 2,000 miles:

New Opti.
New WP.
New 160 stat.
New coil.
New plugs.
New wires.
New O2 sensors.
New fuel filter.
New EGR.
New EVAP canister.
New MAP sensor.
Cleaned out the TB/IAC assembly.
No vacuum leaks.
No plugs arching.

I'm going to change the fuel pump sometime next week. After that, I'm going to get a custom chip for my engine.

It was suggested that, since my car has so many miles (172K), the timing is somewhat de-tuned, considering it has the factory timing chain, which HAS to have stretched a bit, causing the tune to be a couple degrees off, hence my hesitation...It even got real bad when I changed to a generic custom chip that's sold for 93 Z28/Formula/TA's, my car ran horrible. It seems to run somewhat better with the factory chip, it still hesitates, but only when it's warm.

Do 93's have IAT sensors? I have speed density, that's only on 93 f-bodies.

 

Carlosz28.I bought a G.M. code reader at Walmart for $20.00,and it may tell you whats going on.I had my car scaned at the dealer,and had to have all my wires(pass side next to manifold)replaced,seems even if the parts work well,the wires leading to them were toast.Now after my water pump was replaced,and the wires replaced,(and thier connectors),my car runs like new.No hesitation,no back fire,no nothing.Hope this helps.

 

Dude, THANKS.

I'll get that ASAP, and again, it's appreciated.