I'll cut to the chase here. I've posted before about this but have new info now. Last night was pretty COOL outside ( 50 degrees), and the car was in the garage, so it got fairly cooled down. I started it up, and it ran not too bad for a while, and actually held an idle ( at 800 rpm which is higher than its usual 500 rpm) . After about a minute of this, it started getting really rough, and i noticed lots of blue smoke and the smell of unburned gas, and shut it down.

There were two black streaks of wet carbon on the ground under the two tailpipes.

Got the codes. Only a 53 code and a 33( I have the maf disco on purpose).

The 53 is supposed to be high system voltage, so I had my alt tested, and it tested OK. Only putting out 14.9 volts.

What is making it run so rich ??? Is it only the CTS that deterrmines richness ? and TPS ? I actually got a code 15 (LOW voltage at CTS ) once after I drove for 2 miles with this condition, but it hasn't come back. I figure with LOW voltage at CTS, it means it isn't getting the signal from the computer that it is expecting, right ?? So the CTS is probably OK, but just not getting the strength of signal iut wants ?? As in short circiut somewhere ??

btw I checked all the grounds, nice and clean EXCEPT the ground on the block, haven't had a chance to check it yet.

I checked the volts bat the TPS, am getting 0.50, it's the max I can get it to. Cheap analog volt meter might be inaccurate.

What could be causing my rich mixture ?

Thanks


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88 GTA 5.7 TPI Charcoal Grey Bone Stock except for loose muffler which makes it a bit louder than normal.

 

did u test the alt. urself? was it on the engine? Im not electrical specialist, but i would be a little worried about 14.9 volts at idle, but thats just me, but i don't think it would have to much effect on how the car runs. and as far as those sensors, might wanna replace the TPS and see if u can get the .54 without turning it to max.

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88' GTA 350 MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass

 

I suspect your CTS. First, you get a Low Voltage which indicates a prolonged reading equivalent to -40*F. The reason you may not be getting a code now is that the CTS is registering -15*F which is tolerable by the ECM but the incorrect CTS.

The easiest way to test a CTS is with a scan tool. Barring that, just buy a CTS and see if that helps. I suspect it will.

FYI, if the CTS was given a reading lower than it really should be, the engine will run richer and remain in cold start mode. This is similar to a colder T-stat or the T-stat stuck open.

That too (stuck T-stat) should be checked out.

 

Just found out something very interesting! The input voltage from the ECM to the CTS is only 4.1 when it shpuld be 5.0. Where do I go from here ? Is the ECM fried? The ECM input to the TPS is fine (5.0), but the volts to the CTS are low. Why ?

Thanks

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88 GTA 5.7 TPI Charcoal Grey Bone Stock except for loose muffler which makes it a bit louder than normal.

 

Have you checked the CTS? At a normal engine operating temperature of 185-195*F the voltage will be between 1.5 to 2.0 volts, or between 240 to 300 ohms.

It is the resistance of the CTS that is more important and this is how GM tests it. GM doesn't even give a "voltage chart" for the various temperatures...only resistance. So you should measure that.

What you are checking is your reference voltage and it says "you are getting voltage" to the CTS, though not 5.0 Volts. That can be caused by a low alternator output due to idling at low speeds (especially with underdrive pullies). You've proven its getting some voltage to the CTS though slightly less than optimal. Now, you need to measure the resistance, which is REALLY what the ECM is concerned with.

 

I checked the voltage with the engine cold, key on, engine off. That's when I got 4.1 volts. The TPS was getting an even 5.0 volts. And I checked the Ohms at the CTS too. Got 2,400 at 70 F (21 C). Does that sound OK ? Should I change out the CTS ?

Thanks





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88 GTA 5.7 TPI Charcoal Grey Bone Stock except for loose muffler which makes it a bit louder than normal.

 

I checked the voltage with the engine cold, key on, engine off. That's when I got 4.1 volts. The TPS was getting an even 5.0 volts. And I checked the Ohms at the CTS too. Got 2,400 at 70 F (21 C). Does that sound OK ? Should I change out the CTS ?

Thanks





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88 GTA 5.7 TPI Charcoal Grey Bone Stock except for loose muffler which makes it a bit louder than normal.