1984 K5 Blazer Idling Rich-California Emissions-Coolant Sensor?

[CORVAIRWILD]

I drove a 1984 K5 Blazer back from California this past May, and the last few hundred miles the engine started idling very rich. It's got an oxygen sensor on the driver's bank, the electronically controlled carburetor, but what looks like a stock HEI distributor. A friend of mine mentioned that the coolant sensor next to the thermostat could be sending a cold signal, that's making the carburetor run rich like it's cold start. The choke is wide-open. Otherwise the engine runs fine. It's a crate 350 and I've sold the truck, I'm just trying to rectify this rich idle issue. Any help?

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[1987 GMC Jimmy]

I’ve got the same CCC system on my car. It’s not the greatest thing GM ever dreamt up, but it’s given me many trouble free miles. Just to make sure, the SES light is coming on when you turn the key? Does it ever come on while you’re driving or idling? Mine’s super sensitive about rich/lean exhaust, but it couldn’t seem to care less about other things like EGR and CTS functionality. Not like my TBI, which will inform me of any little thing that goes wrong.

When I got mine, the CTS and its pigtail were completely disintegrated so I replaced them. The only way I could tell you for sure if it’s working is with my 34 year old CCC scan tool. Unfortunately, serial data is not as easily accessible on these as on TBIs. It’s worth replacing every once in a while on things that have that type of coolant sensor. And cheap.

Is your mixture control solenoid (MCS) working? It should quickly and audibly go “chicka-chicka-chicka” when you turn the key to ON. This is another thing my Caprice is sensitive about. If the connector at the top of the carb is unplugged, it’ll throw a code immediately. There’s a green test port near the carb for a dwell meter. I had mine professionally rebuilt and setup so I can’t confidently speak to the proper procedure on that and the dwell parameters.

Another thing to consider is the TPS sensor. If the idle voltage is too high, that could be a problem. They more commonly fail with dead spots in them, which would cause bogging, but if the idle voltage is above say 0.6V, that’s a problem.

As you mentioned, the O2 sensor is a worthy consideration.

A plugged PCV line and/or a failed PCV valve can cause issues. If in doubt, replace the valve. It’s supposed to rattle when it works properly. Another overlooked system, is evaporative emissions. There’s a little filter on the bottom of the charcoal canister that I’m willing to bet is crusty, old, and dirty. A bad fuel cap, a clogged charcoal canister, or some issue with the little valve can be problematic. Check your vacuum lines. I had about a million that were broken or completely cracked up.

Finally, I’d suggest you check what the curb idle mixture is set to. It seems to me that later Quadrajets like a more liberal mixture setting, and these are no exception.

This is a comprehensive list. You’ll probably find only one major contributor and a couple of little things that don’t impact your AFR as much but that fixing them will help a little. That’s my experience anyway.

@CorvairGeek might have some other thoughts. Here’s a good page with info on the CCC system to demystify it some. I assumed that you knew how to check most of what I didn’t elaborate on, but if you have further questions, check back, and we can proceed further.

http://www.early3rdgen.com/forum/viewtopic.php?f=11&t=25

 

[CORVAIRWILD]

Hi GMC Jimmy. Way back in the early 90s I was running a small full service auto repair shop, but when things were becoming fuel injected I luckily got into real estate and the car business fell by the wayside. Lucky for me, because all I know but it fuel injection is that little solenoid that goes chicka chicka chicka, the rest of it's all Chinese, even though a few people have explained it to me over the years.

So now that you have given me a lengthy clear explanation of where to go with this, I'm going to get together with a friend of mine from Chicago, who like me is a Pontiac guy, but he also knows some good basics about electronic fuel injection. Like I mentioned up above, I know nothing about oxygen sensors and voltage and square waves. Eventually I'll have to learn and get a scan tool because everything is electronic nowadays.

 

[CORVAIRWILD]

I'm in my shop now, 9:40 at night, and the valve on the carburetor is not making a sound, and I'm pretty sure it was when I bought the truck and started driving it east, and I'm pretty sure because it's the only vehicle I have that has a electronic carburetor. And I jiggled the wires and unplugged it and nothing changed. I also discovered that the lamp on my dash on my diesel says glow plugs, on this truck says check engine, I thought this truck was a converted diesel to gas when I bought it long distance from Craigslist. I even had the guy open the gas filler door and take a picture, but now I know what that lamp says, I just never bothered to look, "Check engine" as you can see in the picture. So at least I'm off to a start, for some reason the valve is not working, either because it's not functioning or because it's not getting a signal from wherever it gets the signal from.

When I bought the truck, and I drove it away for the first time, it was running on 7 cylinders. So I pulled the distributor cap, everything was fine, I pulled the plugs, they were fine. It turns out that the mixture screws were improperly adjusted, and when I set them to smooth the idle, the 8th cylinder chimed in. And it was fine all the way back east, until the rich idle condition appeared. I'm sure it's a simple thing, I just barely know where to start

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[Rusty Nail]

Smart lookin truck!

Ya know the service interval on that one wire oxygen sensor ain't but 30k or so...
Meh @ that green plug
The 2 dollar charcoal canister FILTER is behind the counter at O'Reilly's and you will be HARD PRESSED to find somebody there that has ever sold one before.
I advocate new fuel caps.
And spark plugs...especially that one!

 

[CORVAIRWILD]

Here's the sensor next to the tstat. Does RockAuto sell this sensor? They have a Bosch oxygen sensor for $15, I'll definitely get one of those, but the sensor looks like it has a two wire plug, but it could just be a stock image

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[CORVAIRWILD]

more... I'm also putting on spring shims to correct the pinion angle. No idea why the axle was at such an extreme angle from the drive shaft, this truck is dead dead dead stock.

A little closer look revealed that RockAuto does sell the correct single wire plug, TX1

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[yevgenievich]

The default mixture on that carb is extremely rich. If the solenoid not working or not getting signal, it will run rich.

 

[CORVAIRWILD]

So I need to figure out if the solenoid is not getting signal, or is dead-not reacting to signal. Seems simple enuff

 

[1987 GMC Jimmy]

So yeah, that CTS is super universal. I probably got mine at O’Reilly’s. If your pigtail is in good shape, which it appears to be, I think you’ll be alright.

Second, it sounds like your Check Engine light isn’t coming on, which is a problem. If the bulb is burnt out, that’s one thing, but if the ECM isn’t coming on, that right there could be why your mixture control solenoid isn’t clicking. You can either replace the bulb and see what happens or try to unplug the ECM and see if it’ll trip the light. Whatever’s easier for you.

There are two ways to test the solenoid. You can jump it directly to the battery if you want, and it should click. When you release the connection it should click again, just like testing a fuel injector the old fashioned way. Or you can get that dwell meter, hook the pos. end to the green connector by the carb, hook the neg. end to a known, good ground, and set it to 6 cyl. mode. Again, I’m not 100% on the parameters. I’m thinking 30 or a 50% duty cycle is ideal. Anything more or less will indicate a rich or lean signal. Apparently, the key on clicking test doesn’t apply to all E4MEs, but the only consensus I’ve found seems to point at this test failing to work on BOP applications. For Chevy and GMC, I’m assuming it holds up.

I would start by just jumping the solenoid directly to the battery with some alligator jumper leads and seeing what happens.

 

[CorvairGeek]

Apparently, the key on clicking test doesn’t apply to all E4MEs, but the only consensus I’ve found seems to point at this test failing to work on BOP applications. For Chevy and GMC, I’m assuming it holds up.

I've noticed that as well, but never seen it in writing. I assume it wasn't proper for an Olds or Buick to start clicking when the key was turned on.

 

[CORVAIRWILD]

I thot the lamp between the speedo and fuel gauge was for diesel! So I'll put a bulb in the socket and see what happens. "Checking fuel injection the old fashioned way"???? Hah! I've never worked on FI!!! NEVER! No time like the present...

 

[1987 GMC Jimmy]

I thot the lamp between the speedo and fuel gauge was for diesel! So I'll put a bulb in the socket and see what happens. "Checking fuel injection the old fashioned way"???? Hah! I've never worked on FI!!! NEVER! No time like the present...

Well, on the TBI you can get a 9V battery and touch it directly to the male connections on the injector to see if the injector will cycle open and closed. Great test. I know almost squat about anything later than that, though.

 

[CORVAIRWILD]

Are we discussing newer TBI below? I put the dash together, ALL the instrument lamps now function, inc the CHECK ENGINE. I got both the new O2 and CTS from RA. I'll attempt to install them today.

Then I'll turn to my non functioning heater fan...

Well, on the TBI you can get a 9V battery and touch it directly to the male connections on the injector to see if the injector will cycle open and closed. Great test. I know almost squat about anything later than that, though.

 

[1987 GMC Jimmy]

You can do the same thing for the mixture control solenoid since it takes a voltage signal to actuate just like an injector, but it’d probably have to be jumpered since the pins are recessed. Probably easier to jump it straight from the battery, but if your jumper wires aren’t long enough, the little battery should suffice.