I've had some problems with my engine since I changed the thermostat. Symptoms are:

1. Idles a bit rough when in D
2. All spark plugs get medium black after a few hundred km.
3. It hesitates when starting from a dead stop.

When I changed the thermostat I also changed intake and carb gaskets.

Yesterday I took the car to my favorite tune-up guy but he called me later the same day and told me he had given up. Couldn't find any data on the carb/engine and couldn't find any screws to adjust. He had never seen anything like this before.
All I asked him to do was to test it to see weather it was running rich or lean at different driving conditions, idle, part throttle, WOT, etc. but all he said was "it appears to be running lean".

This sounds a bit strange to me since the plugs are black.
Anyway, I have found a place where I can use a exhaust analyzer but I've never used one of these before. What should I look for to find out what is wrong?? And how do I do it?? Do I only test it at idle or do I have to test it at part throttle and adjust the mixture screws too??

Thanks

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\Henrik
'76 Volvo 244GL
'87 El Camino 305

you probably checked this already . . . but is the choak sticking partially closed?? This would cause it to run rich.

[This message has been edited by Mr. D (edited 05-08-2002).]

I've checked that, it's working fine.

BTW: How much does the ECM interfere with the fuel mixture?? (If any)

What type of vehicle is this in? If it's the 87 El Camino in your signature, then what you have is a Computer Command Control carb. And yes, the mixture is controlled by an ECM. This particular Q-jet uses a solenoid that cycles the metering rods up and down in the main jets approximately 10 times per second, and controls the mixture by varying the on time vs the off time of the solenoid, or the pulse width as it's called. It's possible that the solenoid is shot wich would cause the needles to be in the wide open position all the time. You can usually hear it clicking when the engine is running. It's immediately forward of the air horn just to the left of the accelerator pump rod on top of the carb. You should see one or two wires connected to it. This system was the predecessor to modern fuel injection.

Other possible causes; flooded charcoal canister or a defective canister purge valve, saturated float inside the carb, trash in the needle and seat, or a carb that's simply in need of overhaul.

If you bought this EC used, you may want to make sure the Check Engine light is working, which you can do by simply turning on the ignition. It should light up when the key is on with the engine off. If you don't get a Check Engine light, it's very possible that someone pulled the bulb and sold the car to you, and now it has a code stored that will have to be investigated.

[This message has been edited by Randy Mosier (edited 05-08-2002).]

Did you use the wrong base gasket? Covering up something you shouldn't or visa-versa?


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Regards,
RLK
My Cars (http://home.texoma.net/~rknipe/)

Randy,
you make it sound like this carb can't be adjusted??
I can hear the solenoid when I turn on the ignition. Yesterday I checked the engine light but the bulb has been pulled like you guessed http://www.chevelles.com/forum/frown.gif I have replaced it but not started the car yet.

Base gasket?? If it's the carb to intake gasket, they were exactly the same.

I will check the exhaust today, write down what it says and get back to you.

Not good, the "service engine soon" light comes on and I just read the troubles codes. Five of them!!

13 Oxygen sensor or TPS
21 TPS
23 Mixture control solenoid
24 VSS
41 Distributer pulses missing

#24 is because the speedometer doesn't (read on of my other posts). When changing the intake and carb gaskets I've obviously had the cables for the TPS, MCS and distributer off. What can have gone wrong, they're all back in http://www.chevelles.com/forum/confused.gif

Ok, as a start I tested the TPS in the carb. It's defective. It appers to be at WOT all the time.

Then I reset the ECM trouble codes and took it for a long drive (1h) both cruising and at WOT. Only one trouble codes everytime I tested: #21 -- The TPS.

So the question it how much does this affect the system?? If the ECM can see it's broking
maybe it's not using it.

I still need a lot a help here. What can I do (I don't want to replace the TPS).

Pull the battery cable and leave it off for one minute. (The service manual says ten seconds, but if a little's good, a lot is better in this case!) Then reconnect the cable and drive the car for a while. See which codes reset.

I'd be inclined to lean towards the O2 sensor or TPS as the possible cause. Either can cause an overly rich condition because the car would be in sort of a limp in mode. But see which codes reset and troubleshoot accordingly.

The carb does have idle mixture adjustment screws, they're just buried behind a plug on the carb base. You can remove the plugs by removing the carb and turning it over, then very carrefully cut and remove a small amount of material from the base plate directly beneath the plugs so you can get something on them to drive them out, something like a small center punch. I think you need to use a Torx driver to adjust them, if memory serves. The carb also has a secondary air valve adjustment. This can be checked by opening the secondary air valve by hand and quickly letting it go, and then observe how fast it shuts. It should close the instant you release it and you should hear a good, metallic snapping sound when it slams shut. That puts it in the ballpark, and if you can determine if you need the secondaries to open faster or slower with a little extensive test driving.

And once you get the causes of the fault codes squared away, you may not even need to make any carb adjustments.

You posted your last reply as I was typing my reply.
Yes, the ECM thinks the engine is at wide open throttle. This means the pulse width of the solenoid is very narrow, which is equivalent to raising the needles up out of the jets all the way and leaving them there in a regular carb. It's providing a very rich mixture to the engine.
The good news is, they're not very expensive and should be available at most auto supply stores like Autozone or O'Reilly's.

The solenoid is designed in such a way that if the if it or the TPS failed suddenly, the solenoid goes to the wide open position. The thinking is, if you were passing an 18 wheeler on a two lane road when one of those components failed, you don't want to shut off the flow of fuel to the engine.

[This message has been edited by Randy Mosier (edited 05-09-2002).]

I managed to put the new TPS in and put everything back together. But something's wrong. The accelerator pump nozzle on the left side doesn't work, the fuel goes up and comes out on the top of the carb next to the gasket. What have I done wrong??

EDIT:

I just loosened all the air horn mounting screws and then it worked!?! A can't have put the gasket on wrong can I?? It only fits one way.
When I tightened the screws it stopped working again.

[This message has been edited by morsing (edited 05-20-2002).]

Hmm.. Maybe I've cracked the gasket by overtightening the screws??

Anyway, I have another question now: How do I adjust the TPS?? I've drilled out the plug the the adjustment "screw" like the instructions say, but it's not really a screw. I suppose I have to turn it but I don't know how. I can't get anything in there that can turn it.

I may be wrong, or I may be thinking about later EFI systems, but I thought the TPS was adjusted with a voltmeter. Isn't there a slotted screw hole in the body of the TPS where it's attached to the carb? If so, that's the one you loosen. But, I can't remember which wires you place the voltmeter leads on. But the factory service manual gives you a specific voltage value with the throttle at the closed position.

Morsing,
On the connector to the TPS,terminals are marked A B C.
term. A - 5v reference signal
term. B - signal return to ECM
term. C - ground to ECM
Measure voltage at terminal B, spec for 5.7L v-8 is .48v
Use a DVOM only don't use a analog gauge.


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John
71 El Camino

The voltage should go from .48 to 4.5 according to the instructions. I've got all that stuff down. Right now it goes from .05 to .27.
The TPS is adjusted by a small "hook" that is mounted inside the carb just below the accel. pump arm. The TPS is adjusted by forcing the hook down with the adjustment screw.

There is no accesible screw on the outside of the carb. I had to drill a hole to get to the adjustment pin which is not slotted and is in side a hole only a few millimeters wide.
My problem is purely how to turn this "screw" that I cannot get to with any of my tools??

Do you have a way to post a digital picture? It's hard to picture this mentally.

Well the picture isn't too good but right next to the accel. pump arm is a small round plugged off hole. I've removed the plug and inside is the thing I'm pretty sure I have to turn.

http://62.79.45.155/photos/CarbTPSadjustmentScrew.jpg

Anyway, I've pulled the air horn and I've damaged the gasket but not around the pipe to the accelerator pump nozzle.

I've also checked the TSP by pressing the pin down with my finger and I think it's defective. It only goes between .05 and .27 volts. I think I have to get another one http://www.chevelles.com/forum/frown.gif

Sorry to bring this up again but I got a new TSP today and it's the same http://www.chevelles.com/forum/frown.gif It only goes between 0.05V and 0.27V and not 0.50-4.5 as it's supposed to.
Could it be a wrong one?? They're physicaly exactly the same and it fits into the carb?? Can two TPSes made for this carb have different ratings??

And another thing: Ever since I changed this TPS the first time my TCC is acting up http://www.chevelles.com/forum/frown.gif I have to shift manually to avoid it stalling the engine and I also have to downshift manually all the time while driving http://www.chevelles.com/forum/frown.gif
What could be wrong?? I'm getting really tired of this http://www.chevelles.com/forum/frown.gif
The TCC only starts to work after driving for a while (20-30mins).

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\Henrik
'76 Volvo 244GL
'87 El Camino w/ 305ci
TH200R4, 2.73 10-bolt non-posi
Best 1/4: 18.2@74MPH

This concern your decription of the accelerator pump shot coming out on side at the gasket rather than the correct port. It may be that someone over time has over tighten the air horn (the q-jet top) an caused it to become warped, there is no way to fix a warped air horn except replacement. I would check this as well as the TPS adjustment, good luck

I changed the gasket and that fixed it. I also called my parts supplier and asked about the TPS. He said that since my engine was a type H it was a very late '87 (actually '88) and they might have changed the TPS. He'd have to look into it and will call me back.

They also have equipment to read data from the ECM and he offered me to stop by and he would check it out.

Thanks for your reply.

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\Henrik
'76 Volvo 244GL
'87 El Camino w/ 305ci
TH200R4, 2.73 10-bolt non-posi
Best 1/4: 18.2@74MPH