jdrafke

Well ever since i bought my car in early july it has had a cold start problem which seems to be getting worse. I just did a complete tune-up on the car (plugs, wires, o2, cap and rotor, fuel filter, tps adjustment(.54), timing set at 8* base) However, i failed emissions and the car still starts funny. Also, it seems to want to overheat now when sitting in traffic and i noticed the fans had not kicked on around about 235. In which i then shut the car down and waited. It cools down as i drive so its not the air dam. I was thinking it was the coolant sensor. Since the primary fan didnt kick on and its still running rich almost all the time. Only question is, Can the sensor be bad and not throw a code for it? I dont want to have to replace it if it is not even the problem. Any other suggestions would be good too.-

D Stroy H8

Could be that the sensor is functional, but the fan relay is burnt out. Therefore you wouldn't see a code, but the primary fan (turns on around 200 I think) wouldn't engage. The secondary fan will turn on at about 220-235 I think.

Try this - warm the car up to operating temp, and turn on the A/C. Look at the fans now - if both aren't on I believe you have a relay problem, because the A/C being on should signal operation of both radiator fans.

jdrafke

yes, even if i turn the ac on neither fan comes on. I do beleive that the ac relay fan is broken but my ac has never worked so im not worried about that. Besides im gonna use the fan with a fan switch for the summer anyways. I thought the fan relay might be dead but when i jump the a and b terminals in diagnostic mode the fan will come on. Plus, the problem with the car in the mornings when its stumbling. It will come in and out of closed loop as well(when first started up for the first 10 minutes or so). It sounds alot like the sensor to me but wouldntthe computer throw a code. I checked and i get no codes. Can the fan relay be bad and still work when the terminals are jumped?

D Stroy H8

I'm just about out of info at that point. I can't answer with confidence.

CaptPicardsZ28

I pulled this from one of Vaders threads tonight:

Hope Vader dont mind. I wanted to give credit for this response to the person who made it. Hope it helps....

Make sure you have the correct sensor. There may be as many as three coolant temperature sensors on your engine - One for the dash gauge, one for the radiator auxilliary cooling fan, and one for the ECM reading of engine coolant temperature. The one for the ECM typically has a black (grounded) and yellow (signal) wire in the connector. As I recall, neither of the other two sensors should have a two-wire connector. Also, failure of either of the other two sensors will not set an error code.

jdrafke

thanks for the info guys. Yes, i know of both the other two sensors as well. The gauge sensor seems to be working fine and the the aux. primary sensor is gonna be replaced with a lower one soon enough. However, i thought if the fan switch was bad it would not turn on when i jumped the a and b terminals in which it then comes on. Also, this cold start and stumble problem is really pissing me off. Ive eliminated almost everthing it could be down to the coolant sensor. Im pretty sure im jsut gonna go replace it this weekend if it warms up here. Im hoping its failing and just not throwing the code if thats possible

ULTM8Z

I believe you'd only get a code if the ECM lost the coolant sensor signal entirely. If the sensor it was only giving the ECM the wrong reading, it probably wouldn't throw a code. What happens if you disconnect the sensor?

Coolant sensors are cheap anyway, so it's worth a shot to replace it if all else has failed.

383 rocket bird

Have you given any thought to replacing the oxygen sensor. They are standard replacement parts once they get 30,000 miles on them anyways. Just a thought. -John

jdrafke

Yes, i replaced the o2 sensor during the tune-up about 100 miles ago. K, thanks for the info, im going to repalce the senosr over the weekend. You guys think if it is the coolant sensor and i replace it i could gain some power back? Its felt kinda lack luster even since i bought it but its always had this problem(Fan turning on and off funny and cold start problems)

Another thing is i jsut put some gas in the car and it seems that almost every time i give it some light throttle for a series of more then 30 seconds it stumlbes for a second the tach goes up about 300 rpm and then back to normal. this all happens in about 3 seconds. If i go 3/4 throttle or more it doesnt have any affect jsut at light throttle. Could it be cuz i only put in mid grade gas at speedway or another problem? Keeping in mind i just had a tune-up.

383 rocket bird

Running rich always takes away performance so once you cure your rich condition you will gain some performance back.

383 rocket bird

Also if I remember correctly coolant temp sensors are under ten bucks.

jdrafke

Thanks Guys for all the replies. Im gonna go get that part over the weekend and replace it. Maybe ill gain back some lost hp. Sweet

DON 88T/A

JDRAFKE,post your results because my 88 T/A starts good but has a stumble at part throttle when its cold but if you nail it it runs fine..plus once it heats up it goes away.
Been trying to figure it out for months,and yours sounds just like the problem I'm having...
If all it turns out to be is the coolant temp sensor,thats not to bad..

jdrafke

Ight ill do that, im gonna replace the sensor today after this hangover goes away

jdrafke

K well i jsut fixed the coolant sensor and didnt notice a diff in the performance much. It still stumbles and the fan still hasnt come on. I found out that jumping hte terminals bypasses the relay so im gonna replace the relay in the coming days. The car is still stumbling in the morning. And the idle is still bouncy. Any suggestions on what to look at next. My buddy cronsformula350 also noticed something on my car last week. When i turn the car off or even when its running sumtimes u will hear a buzz or a hiss noise. He says it was the iac being loud. Could this be a problem? Or whats causing the stumbling? Im running out of ideas guys :-(

kidcamarosc

did you check for vacuum leaks??

jdrafke

yes check for vacuum leaks and couldnt find any. Only thing left to check is fuel pressure. I also did vaders test when in field diagnositc mode the car seems to keep coming in and out of closed loop. Is this normal when the operating temp is only a bit above 165? It seems to go into closed loop and then come out every so often. Do u think i should bring the sensor back cuz it may be faulty?

DON 88T/A

Mine does that hissing noise when it shuts off too,not sure if its the IAC valve though..sounds like its under the plenum...I have no vaccum leaks that aI know of...
I do have an AFPR on and set to about 48 psi..I have a decent amount of mods,so I figured the fuel pressure around that, and it feels strong though I have not run it at the track yet...
But I wonder with the extra injector on the cold start adding a little extra fuel if its a bit too much....because once the car heats up it goes away...after it reaches closed loop, the cold start injector ceases to add fuel...but while its still cold maybe all that extra fuel at part throttle is too much? Full throttle no problems...cold or warm..
You got a AFPR jdrafke?

DON 88T/A

And if you haven't already,I would replace that fan relay..because that second fan should be coming on around 220-230...
i doubt that new coolant sensor is bad......

jdrafke

Yea im gonna be replacing the fan relay very soon but its not above 50* here yet so its not to bad yet. No, i dont have a fuel regulator and im gonna disconnect the vacuum line to see if theres any gas in it. U guys think that could cause this? Running low on ideas

87Formula356

just a thought but are you guys sure that the hissing noise ins't just your fuel pump running for a bit longer? my firebird has always done that.