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Electronic Quadrajet runs VERY rich

My friend has an '83 Olds Ninety Eight with a 307 V8 that is running extremely rich.

Symptoms:

- The tailpipe is very sooty. On starting it leaves a large soot stain on the ground beneath the exhaust.

- It is so rich that when starting it barely runs; you must constantly gun the engine to keep it alive. Once the choke opens it will idle, but is very lumpy, and overall running is poor.

- It gets terrible gas mileage, well under 10 mpg. The owner claims 5 or 6!

Assuming I have done my research correctly, it is equipped with an electronic Quadrajet 750. Although I am mostly guessing, I assume there may be many potential causes:

- A float that is losing buoyancy.

- Sensor problem (O2 sensor? TPS? Other?)

- Carb mixture control (solenoid?) stuck full rich.

- Bad engine management computer.

- ????

Initially I wanted to check the floats, but when I realized what I was getting into I figured I better think before I jump. Being middle aged, my backyard mechanic days are from 60's era cars, so I have never touched an electronic carb, plus I have only rebuilt much simpler 1 & 2 barrel models, so I don't want to jump into a major effort unless it is really needed. Not to mention that the car currently runs, and after I "fix" it the car might not.

Questions:

1) Any likely candidates for this kind of problem? How likely are my guesses?

2) Can the float level be checked without completely removing & disassembling the carb? I read one bit that said "remove the air horn." as if it is easy to do in the car, but I have my doubts, like they skipped that pesky little "after removing the carb" step.

3) What is the mixture range that the engine management system can actually control? In other words, if there is an EMS failure can it really make the engine run this rich? From my limited experience with EMS on fuel injected engines, I suspect the their range from full rich to full lean is significantly smaller than might cause this level of problem.

If it matters, the carb #'s are:

17083253 1573FLC

Thanks in advance,

parkerea

Reply to
parkerea
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There's a rebuild house on Ebay that sells these, see

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?ViewItem&category=33550&item=2470144213 for contact info and e-mail them. You can probably pick up a spanking-new rebuild from them for about $200.

Alternatively if you want to do it yourself, you can get cores for parts, such as:

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and old rebuild kits cheap such as:

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But I would warn you against this. If the throttle position sensor is shot (good chance on a carb this old) by the time you buy parts your up in the $200 range and you won't have a carb flow bench or any of that.

I doubt that the engine computer is bad. When deciding if the electronics are bad or the mechanicals are bad, choose the mechanicals every time. This to me sounds like something catastrophically wrong, such as a sunk float.

If all the electrical in the carb is OK, then a standard rebuild kit, and time spent rebuilding the carb will probably fix it. But if any of the electrical is bad, your going to be hosed.

Ted

Reply to
Ted Mittelstaedt

Sounds like one of the problems may be a choke pull off that has stopped functioning. Have they?

Possible

Also possible, along with the MAP sensor or coolant sensor.

Possible.

Possible. Have you checked it for trouble codes, does the check engine light illuminate with the key on engine not running? (can't get codes if the light doesn't work)

Charcoal canister control valve.

Yes, he float level can be checked without removing or disassembling anything.

Thexton Part #370, the float gauge is the piece in the middle in the picture. You merely drop it down the bowl vent and read it against the top edge of the bowl vent slot. it can also be used to measure mixture control solenoid travel by dropping in the D shaped hole next to the bowl vent. (there are two, one on each side of the idle air bleed adjustment) You'll need the other tools pictured if you decide to overhaul the carb.

Quite lean to quite rich.

Yes, rich enough to soot up the spark plugs. But so would a failed canister control valve, an open circuit coolant sensor or a MAP sensor that isn't connected to the correct vacuum port.

I would not attempt overhauling this carb without a strong working knowledge of it and the related systems AND the factory service manual. They tend to be very fussy and will not run very well if not set exactly as they should be. On the other hand, there are plenty of things to check first before you tear it down. Is the choke functioning correctly, does the choke pull off stroke with vacuum applied and is it opening the choke blade the correct distance? Are there stored trouble codes? Do you -hear- the mixture solenoid clicking with the ignition on, engine off and the ALDL jumpered? Is the MAP sensor functional and connected to the correct vacuum port? Are the spark plugs fouled? No point in trying to make it run until you have clean spark plugs since a missfire will throw the MAP signal off and cause a rich condition anyway. You can force the system to go lean by grounding the green MC dwell lead that breaks out of the electrical harness underhood, assuming that you have 12 volts -to- the MC solenoid, and the solenoid is functional, grounding the green dwell lead will hold the metering rods in the full lean position. Grounding the green dwell lead should cause at least a 100 RPM drop in engine speed.

GM has a well documented diagnostic procedure for determining problems, it is called the "System Performance Check." Find it (factory manual or equivalent) and go thru it and see where it leads you.

Reply to
Neil Nelson

Don't the Quadras have problems with the plugs in the bottom of the body? I've epoxied many of them. Looking at one now, can see 4 thru the throttle plate by the primary bores. JB WELD(tm) works for me.

wws

Reply to
Windell

The pre 80-81 non C-3/C-4 ones do. The post 80 C-3 ones that I've seen do not. The post 80 non C-3 ones do.

Reply to
Neil Nelson

Probably way too late but check the metering rod solenoid ,, Ohm value should be online some where. They go full rich with no input or open coil.

Reply to
pearcetim93

only a little over ten years...

Reply to
Brent

I agree. Had this issue on a Cutlas supreme and it was the choke pull off.

Reply to
m6onz5a

The float is sunk..

Reply to
Bob Flumere

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