Question: Advice please

[94LT1]

Hello all,
Had my '94 for nearly 8 years now and not had the need to request any technical support as has always run without problems but that has all changed after a visit to a garage for it's annual UK m.o.t. test (yearly inspection). Briefly:
62k mileage car completely stock.
Emission test runs in 3 parts: 1st fast idle test/2nd fast idle test/natural idle test.
The results for the 1st idle test CO .43%
HC 20ppm
Lamda 1.01
During the second idle test the engine struggled to make the numbers to pass but was close so was revved a little harder to get to temp (?).
Suddenly CO changed from .43% to 10.85%
HC changed from 20ppm to 287ppm
Lambda changed from 1.10 to .72
On the final natural idle test the CO should be .30% max to pass but was now 46.3%
I've checked the codes and only showing a C12.
Just about to take for a drive to see if any new codes set and now the battery is not charging so staying put for the time being.
I've looked at all your very usefull history file of problem solving and suggestions but not really sure what to be doing next!
Any suggestions?

Many thanks,

Steve.

 

[94LT1]

Hello all,
Had my '94 for nearly 8 years now and not had the need to request any technical support as has always run without problems but that has all changed after a visit to a garage for it's annual UK m.o.t. test (yearly inspection). Briefly:
62k mileage car completely stock.
Emission test runs in 3 parts: 1st fast idle test/2nd fast idle test/natural idle test.
The results for the 1st idle test CO .43%
HC 20ppm
Lamda 1.01
During the second idle test the engine struggled to make the numbers to pass but was close so was revved a little harder to get to temp (?).
Suddenly CO changed from .43% to 10.85%
HC changed from 20ppm to 287ppm
Lambda changed from 1.10 to .72
On the final natural idle test the CO should be .30% max to pass but was now 46.3%
I've checked the codes and only showing a C12.
Just about to take for a drive to see if any new codes set and now the battery is not charging so staying put for the time being.
I've looked at all your very usefull history file of problem solving and suggestions but not really sure what to be doing next!
Any suggestions?

Many thanks,

Steve.

Just to add: Car went in working all OK. It was revved pretty hard to get temps up and came out very hot. The next day the EGR didn't cut in as usual and also now have no alternator charge. Could all this and the CO readings be related? Would a PCM failure do all of this?:confused

Thanks again,

Steve.

 

[gmjunkie]

A alternator going south,Could and Will!!
I believe I'd check out the Charging system!!

 

[94LT1]

Thanks for the reply gmjunkie. Got the battery on charge at the moment. Will fire up and see what happens shortly.

Steve.

 

[LT4man]

Before throwing the battery or the alternator out. Check and clean the battery cable connections. Positive and negative on the battery. The grounds on the engine block, too. Make sure they are all CLEAN and tight!

Also check and clean the alternator connections.

AFTER HAVING THE VETTE PASS, DO NOT FORGET TO SAVE THE !

 

[94LT1]

Thanks LT4man
Taking a look now, will update shortly.

Steve.

 

[94LT1]

Hello America
A brief update:
Checked Battery connections and grounds - OK
Put a couple of hours charge in battery (new ac delco battery 12 months ago) and took for drive. When gauge display switched to voltage it varies 12.2V to 13V according to revs. No EGR coming in after start up. Everything else working OK and drives as should. Rev at standstill and rad fan comes in at 230 and cools temp to 222 ish. ambiant is 70. (only drivers side fan kicks in).
Everything seems fine.
Took to garage today for emmissions retest and advised him to abort if it got too hot during 2000-3000rpm test. When collected was told could'nt test as overheated very quickly so he stopped test. I drove home and hit 230 temp in traffic which quickly cooled to 220 ish when drivers only side fan came in. volts show 13v on motorway. Got home and tried restart - not enough in battery to start but noticed EGR pump runs for 3 seconds only with key switch turned to 'run' position but somehow sounds odd (have checked is pumping ok)
Advice please: Should both fans kick in?
Would a 'lazy' thermostat cause the overheat at the garage?
Could the pcm be to blame for all the above?:confused
Btw still only showing the C12 code.

Thanks in advance,

Steve.

 

[gmjunkie]

Hello America
A brief update:
Checked Battery connections and grounds - OK
Put a couple of hours charge in battery (new ac delco battery 12 months ago) and took for drive. When gauge display switched to voltage it varies 12.2V to 13V according to revs. No EGR coming in after start up. Everything else working OK and drives as should. Rev at standstill and rad fan comes in at 230 and cools temp to 222 ish. ambiant is 70. (only drivers side fan kicks in).
Everything seems fine.
Took to garage today for emmissions retest and advised him to abort if it got too hot during 2000-3000rpm test. When collected was told could'nt test as overheated very quickly so he stopped test. I drove home and hit 230 temp in traffic which quickly cooled to 220 ish when drivers only side fan came in. volts show 13v on motorway. Got home and tried restart - not enough in battery to start but noticed EGR pump runs for 3 seconds only with key switch turned to 'run' position but somehow sounds odd (have checked is pumping ok)
Advice please: Should both fans kick in?
Would a 'lazy' thermostat cause the overheat at the garage?
Could the pcm be to blame for all the above?:confused
Btw still only showing the C12 code.

Thanks in advance,

Steve.

If the AC is running 1 fan should run all the time and the 2nd should come on at approximately 228*!If the AC isn't running the first fan should come on at 228* and the second should come on at about 234*! I'd say you probly have a alternator going south,you should have closer to 13.5-14V running at idle!! Low voltage will cause the cooling fans to run slower than they should too!!

PS It isn't really over heating till it's past 245*!!

 

[LT4man]

Proper charging rate at idle and above is 13.8-14.4 volts. If your alternator is only putting out 13 volts at idle, I would point my finger at the alternator. Your alternator has the voltage regulator installed inside.

A lot of folks sell alternators (rebuilt, reman & new) for your Vette.

I have dealt in the past with Motor City Reman out of Detroit. Also, Nations Auto Electric in Cape Girardeau, MO. Both have excellent products and customer service.

PLEASE DO NOT FORGET TO SAVE THE !

 

[94LT1]

Thanks for the advice, 1st thing I'm going to do is change the thermostat to see if this cures the overheat during the emmissions test - it's at least 8 years old so long overdue regardless. Then I'll look into the alternator - will this involve the pcm in any way to operate? (p code engine) or does it operate independantly?
LT4man, Cape Girardeau sounds an interesting idea, definately like the idea of some time out, problem is, would have to stop off at Disneyworld on the way over with the kids.:W
Now this is beginning to sound very expensive......

Steve.

 

[gmjunkie]

I believe I'd check out the charging system first,Low voltage and possible AC voltage slipping past the diodes in the alternator can make all sorts of things go Hay Wire and Scramble the ECM's Brain!! These cars are designed to run at higher temps for several reasons!

 

[94LT1]

Thanks gmjunkie,
Have a thermostat coming tomorrow, will flush system, fit stat and (maybe) pump while I'm there then move on to the charging problem and will update with news.

All the best,

Steve.

 

[John Robinson]

Another reason for high temp

Before you start replacing the thermostat have the radiator cap tested to see if it is holding pressure. Your description of the temp you are seeing is almost the same as I was experiencing. My cap would intermittently hold pressure and then not hold pressure. Put a new cap on and now the temp normally runs about 208 but will climb up to 216 or 220 in very slow stop and go traffic on 80 Plus days.

As the others have said I think your alternator has gone south. In my experience these problems are usually a combination of a couple of small problems coming together. You have not said but if I were you I would use a voltmeter to check the voltage from the alternator at the battery just to verify that the gauge in the car is not off.

I have a trick to measure voltage with a voltmeter inside the car. What I have done is gone to Radio Shack and they have a cigar lighter that has a switch and fuse in it with leads about $5.00. The leads are positive and negative so I put alligator clips on them and then hook them to the leads on my digital voltmeter. Now you can see the voltage and how much voltage drop you have when starting which should not go below 10 volts. This is a good test of the condition of the battery. With a friend riding along watching the meter you can follow the output of the alternator over a period of time to see if it is breaking down with heat etc.

This is particularly useful on cars with idiot lights instead of meters.

Let us know which one of us has come closest to the solution for your problem. Bragging rights are everything.

 

[94LT1]

John,
Excellent advise, will put some time in over the weekend on it and update.
Got to keep Sunday clear though - have tickets too see your fellow countryman sing a few songs, twang a few guitar strings along with his mate on a saxaphone. Better not mention his name though - he chose a pale blue (56?) thunderbird rather than a vette for one of his video's.

Steve.