Temperature related problem

[monkeyspunk77]

Hello everyone,

I have a problem and wanted to see if anyone has come across it before.

I just got the car 2 weeks ago. 3 times now I have experienced the same problem. It happens when the car is cold (having sat overnight or at least 8 hours in – 15c / 0 to 5F temps). It will start and run normal at first, accessories on, defrosters, front and rear, blows heat, radio works, drives fine.
I should also note that every time the block heater has been plugged in for at least a good 2 or 3 hours.
Driving for about 20 to 25 minutes before it acts up.
When the problem starts I notice the far right hand part of the clock display dimming out. The HVAC system intermittently shuts off and starts up again. The Tach needle falls down to zero, at first it will sporadically jump back up but then gives up all together. One new symptom I just noticed yesterday is a dimming of the dash lights, and when I turn on the rear de-froster, it looses a large amount of power.
First two times I shut the car off shortly after symptoms began, let is sit for about 10 minutes and it started and ran fine.
Last night I drove on it a while longer. I was on the highway and just a small distance from a town so I pushed on till it was walking distance. Then I pulled into a driveway and shut off the car. Waited 2 to 3 minutes and tried to start the car. The engine cranked strange and wimpy, didn’t catch. I let is sit 2 or 3 minutes more, still cranked slowly but with a bit of throttle, it started.
Driving after this point was when I noticed the power loss with he de-frost on and the dim dash lights. Also, this was the first it happened in the dark.
While driving it is still very smooth, no missing or odd noises, just a real slow down with heavy electrical load. The transmission shifts normally and the cruise control continues to function as well.
I drove 5 minutes into the town, parked the car again and went for a walk (maybe 5 to 7 minutes). Came back and it started no problem, all symptoms gone.

So basically, after the heat has had a change to migrate into the extremities of the engine, everything is okay.

I’m thinking of two things right off the bat; a short in the Alternator that it temperature sensitive or a problem with the wiring harness at the back of the engine. I’ve read mention of a heat related problem with this wiring in higher mileage SHOs, but never any real specifics as to the location of the harness or circuits affected.

I’m pretty confident that I’ll track this down, but if anyone can save me doing diagnosis in this frigid weather, I’d be most grateful.

Brad
’97 SHO

 

[Ian Macoomb]

Electrical gremlins are sometimes caused by a weak battery or a failing alternator. If you have another car you can borrow the battery from, install it in the SHO and see if the problem goes away.

 

[99V8SHO]

I remember reading that the tach failing was one of the first signs of battery and/or alternator failure.

 

[roland]

this is offtopic but your SHO looks dead sex 99v8SHO :<
I want a black one, was about to buy a 98, but it got sold before i could get my hands on it!

 

[DavidT]

do you know if your sho is modded? VAK perhaps? I had a VAK that had a bad relay. It acted very similar to your symptoms.
(Vaccuum Accessory Killer) It shuts down the alternator at WOT. Mine would not let the alternator resume AFTER WOT. UNLESS I turned the car off and let it sit for a few hours. Of course if this is true, you will have a battery light during the problems)

 

[shoguy98]

My Sho Had similar problems when my Alternator died. The car ran fine with all accessaries on and running on battery power alone. As the battery started to get drained, all kinds of strange electrical problems occured with the accessaies shutting themselves off one at a time based on their importance. Luxory items such as the radio went first. Lights dimmed to conserve enrgy. Guages started jumping spuratically.

My car also had all kinds of electrical problems a few months back. Dimming lights, non stop blinking anti-theft light, etc... Problem was the battery cables or terminal ends. The terminal ends needed to be replaced and the ends of the wires need to be stripped to expose fresh wire. No electrical issues sine then.

 

[monkeyspunk77]

Thanks guys. I changed the Alternator last night after the car quit on my completely. It seemed as thought it was running on the battery and finaly drained it. I also put in a new battery at the same time. It's running fine now, but the dash lights are dim and I only get 12.2 volts or so at the battery with it running. I'll drive on it for a few days to see if things improve.

 

[Ian Macoomb]

12.2? That's bad. Does it change if you increase the rpms? Do you have a battery light on the dash?

I think you've got a dud for a replacement. It's quite common.

 

[monkeyspunk77]

Okay, here's my latest idea, any thoughts?

These cars don't have a voltage guage, so there must be a light. My dash does not have any charging system lights coming on, so if the bulb is burnt out, that could prevent the field in the alternator from getting the exciter voltage, right? I think that these bulbs are geeneraly wired in series...

What a p.i.t.a., looks like I'll be freezing my bits off in the garage again tomorrow.

 

[Ian Macoomb]

I don't think that that's the case. There's a separate output from the regulator just for the bulb for the battery light. Maybe a previous owner pulled the bulb?

Does the battery light come on when you put the key in and put it to run (but not start)?

 

[SHOZ123]

You need to charge the battery up if it was discharged and you just put in a new alternator. Otherwise you are asking for another alternator failure.

The battery should read 14.4V or higher at 1500 rpm with the new alternator.

 

[nik97]

Do you have a Battery light with KOEO? The charge light is powered by the "I" circuit wich also powers up the voltage regulator on the alternator. There is a resistor in parallel with the charge bulb so the voltage regulator will still have power if the lamp burns out. It sounds to me like you have an open in your'e I circuit.

 

[nik97]

Check the voltage at cicuit 904(light green wire with red trace) at the alternator connector. Should be 1-3 volts key on and 13-15 volts running. If you get good readings check cicuit 35(orange wire with light blue trace)for source voltage.

 

[monkeyspunk77]

There is no light with the KOEO so I'll check the bulb and look for voltage at the Alt. harness before I do anything else.

Thanks again for the info.

 

[monkeyspunk77]

I hooked up a multimeter today and watched the voltage as I was driving to work. It wasn't charging when I started it up. Just for fun I drove to work anyway and found that it began charging about 20 minutes into the drive.

I also noticed that when it does not charge, the battery light, air bag light and I think a few others do not come on with the KOEO.

I still haven't been able to check that 904 circuit yet because every time I am able, the problem goes away.

 

[nik97]

Check 904 cold. Then check it hot. Sound like a bad connector that is only making a connection when it warms up. Also check circuit 35 for 12v KOEO. If you want I can give you all the related inline connector locations, style, and color to make backprobing easier. I can also see if the fuse for this circuit protects the other indicator lamps you mentioned...could be a bad connection right at the battery junction box.

 

[SHOZ123]

FWIW with a charged battery and normally operating alternator, the voltage should be the highest for 15 minutes or so after starting and while driving. This is to recharge the battery from the discharge of starting. It should then drop off and the voltage finally determined by temperature and condition of the battery.

 

[monkeyspunk77]

Nik97, if you have that stuff it would be awesome!

 

[nik97]

Yea sure. I'll PM you with whatever you need. Let me know what circuits(904 or/and 35) and also which warning lamps are inop when not charging

 

[monkeyspunk77]

Nik97, it would be great if I could get both 904 and 35, I'm hoping to nail this thing down for good over the weekend. The Battery and Air Bag lamps both stay out when it's acting up.

Interestingly, this evening I noticed that banging on the dash above the radio / gauge cluster caused the battery lamp to flicker a few times and then the charging system came back on line. Hopefully it is jsut a short in that area.