Couple of C4 Questions

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Nails84

CCCUK Member
Having only had my C4 a few days I am still in the new car anxiety stage.

I took the car out this evening and when I got back I left it idling for a bit, the engine temp rose to the point where the fans kicked in fairly quickly. A quick Google suggests this is fairly normal for the C4 and LT1 as they do run hot. So is this OK?

Also, the car seems to be idling about 600rpm when fully warmed up. Is this a bit low? If I hold the revs at 1000rpm in neutral the car gets a bit "shakey". It is fine as you move past that point. When driving I am not getting any hesitation or signs of miss firing. Normal or not?
 
Steven Smith

Steven Smith

CCCUK Member
These cars do run hot, the fans don't come on until 225°F (107°C).
I fitted a separate thermostatic controlled fan controller, article was published in the magazine last year, so I can get the fan on earlier.
My fan now comes on at 194°F which I feel much happier about, I also put a slightly lower temperature operating thermostat in it.
I think 600rpm is about right if not a little high, can't remember off hand.
Test the TPS should be 0.54v with ignition on but engine not running.
 
teamzr1

teamzr1

Supporting vendor
To get the correct answers for your questions you need to state what year/model and type of engine & tranny as answers would change
by me when knowing that

The engine is controlled by the Engine Control Module (ECM)
Within that is a calibration/tune that is burned into an E-Prom

Looking at a 1991 C4, we see what settings GM set :
If C4 is still totally stock and still using the stock tune

1. ECM does not command first fan until 104 C (220 F deg) and then you see what is commanded at higher coolant temps
GM st these high, but that was only to assure for smog testing
Too hot for best performance, so when I tune these I lower those values

2. Depending on if auto or manual tranny the setting will be different as to commanded setting of engine RPMs
I also change those values depending on the car's needs

As example, you can see when the coolant temp is 80 C degrees, the ECM command idle RPM to 750 RPM
You see in that idle table as coolant temp changes the ECM commands RPMs differently
(again different tranny type the values would have been set lower)

Also, there would be different tuning tables for both of these functions if the A/C is off or ON

c4ectrpm.jpg
 
N

Nails84

CCCUK Member
Thanks, mine is a 1992. I will get one of the Corvette specialists to look at it but overall it drives very nicely and pully very well with no hesitation throughout the rev range.
 
N

Nails84

CCCUK Member
My idle is totally normal then. Thank you!

My only concern left is the vibration through the car at 1000rpm when stationary in neutral.
 
teamzr1

teamzr1

Supporting vendor
Could be a number of things

1. simply coming from clutch and maybe normal
2. The ZF manual tranny for your year was the best of them as it was designed for 450 ft/lb torque and gears were
so tight meshing caused a bit of vibration, also, will be felt in the tranny shifter at idle
3. Check motor mounts, maybe too warn, watch engine at that idle RPM and see if it is moving right/left too much
4. Maybe needs a tune-up and maintenance done
5. Maybe a weak U-joint off driveshaft
 
SearchShane

SearchShane

CCCUK Member
The engine is designed to run hot, The fans kick in at a certain temperature by default, the previous owner of my C4 has installed a flick switch to manually put the fan on before the auto-trigger. Id suggest this if you're going to be cruising in fairly low speed long sessions as I did in Stockholm every week.

The car getting "Shaky" when idling at 1000, I had this issue, but guess what it was?

The door panel were knocked loose, so they rattled when stood still.. All I had to do was re-secure the door panels and it went away.

You're now a fellow proud owner of a Corvette, these cars are amazing, but they do need plenty of maintenance and work doing. I'm learning as I go (I knew nothing about cars when I bought my C4)

Good luck and most importantly, ENJOY!
 
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