emissions repair questions for an 87 5ktcs

[syljay]

> Date: Sun, 4 May 2008 16:06:29 -0400 (EDT)
> From: "David M. Yentema" <yentemad at rider.edu>
> Subject: Re: emissions repair questions for an 87 5ktcs
> 
> 
> As Huw said, I meant the cold start valve, but i'm not convinced that is 
> the problem... Same with the ISV, i tested it today, and it is working fine. 
**** Dirty ISV valves work most of the time, until they dont. The gunk 
inside the ISV valve reacts to cold, heat, moisture with resultant 
changes in viscosity, and that is when the valve will stick.
It is easy enough to remove the ISV and clean it with carb cleaner.

> I think it might have something to do with my ignition system. the 
> connectors on my coil are corroded slightly, rotor is worn, and the spark 
> plugs are the wrong ones. I put the dual electrode bosch plugs in there 
> before i new any better... 
**** BTDT.
Distributor cap will arc internally under certain temp, humidity 
conditions. This will result in crossfire and bad idle and poor 
performance. This usually clears up after engine warm up.
Bad Plug wires work ok,  until you put engine under load . . then they 
wont work and you get misfire.
If the cap has many miles on it, replace it along with rotor and 
plugs. Or, at least remove the cap and examine the cap insides for 
carbon tracks . .clean it well and dry it.

> 
> One other bit of info, sometimes when sitting at a red light or something, 
> the car will sound like it is missing horribly for a few seconds and during 
> this the fuel distributor buzzes at an irratic rhythm 
***** Dont know about the buzzing, but the misfiring could be due to 
cap, rotor, plugs as stated above.

Regarding High CO readings during emissions testing.
1. Correct the idle speed problem - - this may resolve the CO problem 
if you get idle to 900 where it belongs.

2. Slight misfiring will normally produce higher hydrocarbon readings 
. . .maybe it affects CO also.
Misfiring means more fuel in exhaust, O2 sensor reads that, computer 
leans out mixture, now it misfires more.

3. Bad O2 sensors will produce weird symptoms also. How old is yours? 
O2 sensors only last 30 k miles or so. If yours is old, put in a new one.
Sometimes the heating element inside the sensor fails. The sensor 
works ok when driving, but stops working when idling (not hot enough). 
The computer will revert to "Drive Home" mode and not adjust the 
mixture via the DPR. This results in a lean mixture, which can 
contribute to lean miss.

SJ in NJ