93 Z28 LT1 Stutters & Stalls at Operating Temp

wolfspyryt · 08-03-2010, 10:38 PM

Just Purchased a "Mint Condition 93 Z28 w/ 87K miles and the 6 speed. I have 2 concerns at the moment.

1) Temperature is on the edge of "Red" when driving around town ... Middle of gauge when on open highway. Fans come on at higher temp.

I live in southern Wisconsin ... so HOT & Humid. I have read that the LT1 runs hot ... but this seems a little excessive.

2) Once warmed up, on low to middle RPM acceleration the car "bucks & lurches" like dumping the clutch. When car is cold it runs great.

I have NO history on the car ... But it is very clean throughout.

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Injuneer · 08-03-2010, 11:27 PM

You have 2 fans. First fan should come on at 226*F, second fan at 235*F. Check the relays, in the box under the hood. Check radiator to be sure fins are clean, no bags stuck in front. Check level to insure radiator is full to the very top of the fill neck. If there is any indication of air in the system, use the two bleeder screws on the thermostat housing and the top hose to vent the air. Do not dribble coolant on the Optispark distributor.

Misfires when fully warmed up are often traced to faulty O2 sensors. With the 93's speed-density A/F ratio control, problems with the MAP sensor can cause issues, although that would be less temperature sensitive. There can also be problems with heat soak causing the IC module or the optical cam position sensor in the Optospark distributor to break down.

wolfspyryt · 08-03-2010, 11:44 PM

Injuneer ... thanks for the helpful suggestions. Will check these possibilities in the morning.

Is it possible that the 2 issues are related? Such as the stumble issue is causing the higher temps?

Is it possible that both are caused by a faulty sensor once it is in "open-loop?"

speedygonzales · 08-04-2010, 05:47 AM

Quote:

Originally Posted by wolfspyryt

Is it possible that the 2 issues are related? Such as the stumble issue is causing the higher temps?

Not likely.
One thing that is really easy to do to see if the problem is from closed loop control is unplug an O2. This forces the PCM into open loop all the time. If the stumbling problem goes away then, you know the problem is with the controls and not a thermal breakdown.

94blackonblack · 08-04-2010, 10:25 AM

my 94 z was doing this i baught a new temp sensor but it didn't seem to solve my problem i changed the plugs and wires didn't work it turned out to be a faulty temp sensor plug the way i checked was i unpluged the temp sensor and ran the car didn't do it at all reconected the temp sensor and it was fine hasn't done it in over 6 months (it all started after i replaced my opti that is one of the sensors you have to unplug to replace the opti) hope this helps

wolfspyryt · 08-04-2010, 12:22 PM

Thanks for the help everyone ...

I found 2 pieces of cardboard in the "air dam" which removing helped it to cool down faster when I hit the higher speeds.

It still heats up quickly to "red" when idling. Once I start moving, it comes down, wher before it would stay HOT. It is still not right.

When it gets warm at a stop light, it will still stumble under acceleration. Stumbles HARD when I accelerate Hard. Feels just like starting in 3rd or 4th gear from a stop. It really bucks.

When car is cold, It runs superb ... smooth, strong.

I only hear 1 fan kick on ... kinda loud. So I should probably verify both fans operation next.

AC is inoperative, and the fans DO NOT come on with AC, MAX or Defrost. Any ideas on that?

Thanks again to my F-Body Brothers and sisters ...

Terry

wolfspyryt · 08-04-2010, 12:49 PM

Primary Fan IS coming on at the first line before "red."
Secondary Fan does NOT come on at all.

I swapped relays and the secondary fan STILL DOES NOT work ... so of course I swapped back.

rclearyiii · 08-04-2010, 02:32 PM

May be a issue with the coolant temp sensor..the one in the waterpump. That sends data to the pcm that controls when the fans kick on.

Injuneer · 08-04-2010, 05:21 PM

Or maybe your dash gauge is not accurate.

rclearyiii · 08-04-2010, 07:31 PM

That is true Fred...a good point. Could a faulty temp sensor also cause the poor engine performance he is having? I am thinking it could but know you are more knowledgeable on the lt1 setup.

wolfspyryt · 08-04-2010, 09:03 PM

Thanks everyone ... I appreciate the advice & suggestions.

I am not a parts changer ... don't have tons O' Cash if ya know what I mean.

Took it out on the highway tonight. Temperature guage was on the "3/8" hash-mark, where my other GM's seem to run. At 70mph in 6th, I try to accelerate on a flat road and it bucks and kicks, same as it does from a dead stop accelerate (mid to wide open throttle). Temp starts to climb ... then it settles back down. Does the same thing when driving around town. If I baby it ... stays cool until idling. If I drive a little more aggressive (mid-WOT) it will buck and kick and heat up. I am not losing any coolant.

I also smell gas in the back of the car and I do not believe it is a leak.

What software and connector do I need to hook into the cars computer?