Carburetor question
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5.0 and 5.7 Discussion, Carburetor question in Cadillac Engine Technical Discussion; I have the '87 Brougham with the Rochester 4bbl. I am not a mechanic, so I am at the mercy ...
  1. #1
    ReagansRollsRoyce is offline Cadillac Owners Fanatic
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    Carburetor question

    I have the '87 Brougham with the Rochester 4bbl. I am not a mechanic, so I am at the mercy of all service stations.

    Story first, then 2 questions:

    Story:
    A few months ago, the car started shaking in idle and hesitating at stoplights. I was told the carburetor needed to be rebuilt. It was rebuilt by a GM dealership.

    For about 3 months, the car ran perfectly...seamless off the line, smooth as silk on the road. It was back to running like a RWD Cadillac again.

    Then, last month, it started to shake and stall again. Having just moved to a new area, I brought it to the local Cadillac dealer. The report says he checked all vaccum lines, diagnosed Code 23 (Mixture Control Solenoid) and Code 56 (Exh. Rich) a defective Mixture Control Solenoid. He replaced the solenoid (and the TPS sensor--no cost, which he broke in the process) for $500 (with $90/hr labor, I really got hosed). The car stopped stalling but still hesitated, shook at idle, and developed a little highway shake too.

    I brought it back. He took the car back, "adjusted" it (free, because I said I was not paying for nothing). He said this was "the best he could do" and that it needed a new carburetor "if I wanted it to run any better", for which he quoted the price of $2,000. I restrained myself from bursting into laughter and left.

    For about 2 weeks the car did not shake at idle, but continued to hesitate, and vibrate on the highway (steering wheel and something like a book left on passenger seat noticeably vibrate). The shocks are heavy duty and less than a year old, as are all parts of the suspension--arms, links, etc.

    In the last week it has gotten worse. The car now shakes slightly at idle, and rather badly at idle with the a/c on, so badly at one point that the Check Engine light came on. However, it flipped off again by the time I got to the parking lot and did the "paper clip trick" to make it flash codes...all I got was 12.

    On the highway ride: I realize my dad is right: it might be caused by the tires being out of balance...1 is 1.5 years old with 20K, the other 3 are 8 months old with 8K, all Mastercraft ...so I am going to have that, and a rotation done before I proceed about the carb.

    Questions:

    It does seem like my carburetor needs to be replaced so:

    1. Does it really cost $2K to do it? That sounds pretty outrageous to me.

    2. If I do get a new (they're all some form of "rebuilt" now, aren't they) carb, where should I get one from?

    3. Or should I trust a reliable mechanic to either fix my carb or get a reliable rebuilt carb? Or buy my own carb, then bring it to him?

    Note: A friend who's lived in my new city his whole life has recommended someone he considers a reliable mechanic so I'd probably not bring it back to Cadillac and its $90/hr labor. I just don't want to bring the car in, and then have him put a crappy rebuilt in there.

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  3. #2
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
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    Re: Carburetor question

    I'll try to get back to you shortly, just busy, but there is no reason to ever replace a carb unless it is DAMAGED. Just fix. They are very very durable. They just need proper attention.

  4. #3
    ReagansRollsRoyce is offline Cadillac Owners Fanatic
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    Re: Carburetor question

    Quote Originally Posted by N0DIH
    I'll try to get back to you shortly, just busy, but there is no reason to ever replace a carb unless it is DAMAGED. Just fix. They are very very durable. They just need proper attention.
    Thanks...yesterday the CE light came on again and I paper clipped it and got a 45 (I miswrote that as 56 before, my mistake) again, so burning rich again.



    The shaking was caused by a bad alignment...so that's done.

  5. #4
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
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    Re: Carburetor question

    Have you checked the O2 sensor to ensure it isn't dead? I think it dies thinking it is rich.

    Check for roughness with different engine speeds, say D instead of OD on the highway. You can do over 100 mph in 3rd easily, so don't worry about rpms.

    So if you feel roughness at 55 mph, drop to 3rd and see if it changes. Wheels will not change, but engine rpm will, if vib changes, engine...

    Try this. Start the car with the air cleaner off and the vacuum line plugged. Let it idle, engine warm (choke fully opened). Ensure heater hose IS attached to choke housing. This IS needed for proper choke operation. Pull a large vacuum line like a PCV line and disconnect the valve from the end so the engine will stall. (holding the ILC back helps), listen for clicking. If yes, then carb is likely trying. If not, there is a problem with the M/C solenoid.

    It defaults rich if it loses power or fails.

  6. #5
    fullserviceman is offline Cadillac Owners Fanatic
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    Re: Carburetor question

    If you did want a reman. carburetor rockauto.com has them for $353 whicc imo is still high. They are easily rebuilt by any decent local mechanic. It is only 4 bolts to put on very simple if I remeber correct. But this should be a last resort once you know it is the problem. NODIH knows what hes talking about. Personally the dealer is the last resort for us unless the vehicle is under warranty. it takes $2000 to get anything done here it seems

  7. #6
    joe_padavano is offline Cadillac Owners Member
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    Re: Carburetor question

    You didn't say which engine you have. If it's a 307 Olds I have a suggestion. I recently rebuilt the electronic Qjet on my 86 307, but the car continued to run full rich at idle. New O2 sensor, new ignition, etc, etc. Turns out that the problem was the air diverter valve on the air pump. The way this system is supposed to work on the 307 is that air is supposed to be injected into the manifolds when the engine is in open loop mode (before the O2 sensor heats up). Once the computer goes to closed loop, the air diverter valve is supposed to redirect the air injection to the catalytic converter. The problem on my car was that the diverter valve had gone bad and the engine was getting air to the exhaust manifolds all the time. The O2 sensor saw this as a too lean condition and ran the mixture control solenoid at full rich. I replaced the diverter valve (over $70 for the apparently solid gold part!?!) and I was then able to properly adjust the idle needles and the MC solenoid. Of course, the reason why the diverter valve went bad in the first place is that all three check valve on the air injection pipes were bad, allowing hot exhaust gas to get back to the diverter valve.

    You can easily check the operation of the diverter valve. First, with the engine cold, start the car and run at idle. Immediately disconnect the hose from the diverter valve to the pass side air injection manifold and also the hose from the diverter vavle to the converter air pipe (near the firewall). In open loop mode you should feel air pulses from the manifold hose but not the converter hose.

    Now run the car to warm it up. The factory manual actually recommends running the engine at 2000 rpm for a couple of minutes to heat the O2 sensor. With the engine running at idle again in closed loop mode you should be able to feel air pulses from the converter hose but not the manifold hose. If you get any air to the converter in the first test or to the manifold in the second, the diverter is bad and this may be your problem. Note that the problem may also be the vacuum valves that operate the diverter, so some additional troubleshooting might be required. The factory service manual spells out this testing in detail.

    This was an obscure failure and it took me several weekends of checking things on the car before I finally nailed it. Of course, I do all my own work (so there are no labor costs) but I also hate to buy any replacement parts until I've proven what went bad. The problem is that if you have to pay someone by the hour to troubleshoot, you rapidly run up a large repair bill.

  8. #7
    Johnny Bravo is offline Cadillac Owners Fanatic
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    Re: Carburetor question

    Quote Originally Posted by ReagansRollsRoyce View Post
    I have the '87 Brougham with the Rochester 4bbl. I am not a mechanic, so I am at the mercy of all service stations.

    Questions:

    It does seem like my carburetor needs to be replaced so:

    1. Does it really cost $2K to do it? That sounds pretty outrageous to me.

    No, they burned you for $500 now they are throwing out another wild number to see if you'll bite. Never ever use a dealer service department unless you have a new car under warranty period.
    They are a bunch of theives.


    2. If I do get a new (they're all some form of "rebuilt" now, aren't they) carb, where should I get one from?

    Fed Ex ground service your carb to this guy, he'll fix it right, with a five year warranty:

    eBay Motors: 1981-1990 Quadrajet W/Climatic Choke 5 Year Warranty (item 8049066841 end time Jul-07-06 12:27:51 PDT)

    But first find out if you have a massive vacuum leak somewhere. With all the hoses and sensors on the 307 it's easy to get a leak. Especially if someone has been carelessly monkeying around in there.


    3. should I trust a reliable mechanic to either fix my carb or get a reliable rebuilt carb? Or buy my own carb, then bring it to him?

    The hard part is finding a honest mechanic. You don't want to try out someone new on a potentially expensive situation like this.
    You need to ask around, and try different places with easy jobs like oil changes, tire rotations, etc. If they do a decent job at a fair price perhaps they can be trusted with something more complicated.


    On the other hand, replacing the carb is a fair easy job you could probably do yourself in an afternoon with simple hand tools. Autozone has an online repair instructions on their web site, and you can ask advice here as well.
    .

    .....

  9. #8
    ChiTDI is offline Cadillac Owners Member
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    Re: Carburetor question

    [quote=N0DIH;756869]Have you checked the O2 sensor to ensure it isn't dead? I think it dies thinking it is rich.


    Nodih, you are too much.

  10. #9
    cadillacdeville's Avatar
    cadillacdeville is offline Cadillac Owners Fanatic
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    Re: Carburetor question

    sorry to thred jack here but I just bought an 1989 Brougham and replaced the plugs change the o2 sensor and rebuilt the "electric carb" installing a new TPS switch while I was in there now it takes a few pumps to make it start and then it doesn't matter how long it warms up when you put it in drive it almost dies but drives great down the road and idles a little rough at stop signs not much I just rougher than I think it should and if you stop it and kill it then wait like a minute you have to pump the gas to make it start and it'll try to die when you put it in dive again I'm not new to working on cars or rebuilding carbs although this was my first electric. could this maybe be that AIR diverter valve. Also one more ? is it possible to switch to a older style Q-jet like one from a 77 sdv? any help is very welcome.

  11. #10
    N0DIH's Avatar
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    Re: Carburetor question

    You can, but the PCM will be ticked about it and always give you CE lights and TCC won't work at all, timing will likely be messed up too because it will back off due to the check engine light.

    Sounds like I need to get into the E4ME/E4MC carb rebuild business!! I know them well, which is puzzling why so many mech's can't seem to get them right. They really aren't that hard. Really! Granted, I have messed with them for a long time, I guess experience pays too.

    Sounds like idle circuit is not working well. Check the vacuum hoses. Especially the larger ones under connecting to the carb baseplate (PCV, Canister Purge and power brakes). Remember with a ride that old the lines are likely very brittle and hard and break easily when you mess with them when you change a carb out.

    The E4MC (hot air choke) or E4ME (electric choke) carbs are the same old carb as any Q-Jet, with the main metering circuit revised to have a M/C, Mixture Control Solenoid installed to physically cycle the metering rods up and down as commanded by the ECM. Idle circuit and WOT (4BBL's) are unchanged. So if you are having idle issues or WOT issues, look away from the computer. If you are seeing part throttle, then look at the computer. The ECM does have some say in the matter at idle, but not much as little air is flowing, so the majority of the fuel control is still the old fashioned idle air bleeds under the carb, which are capped off. Please do NOT adjust them!

    The M/C solenoid has a rich stop, and a lean stop. On the 1985-up cars, most were changed to have the rich stop as fixed and non adjustable. Lean stop is still adjustable. This is simply how far up and down the M/C solenoid is allowed to travel. The TPS is cruical to be adjusted correctly, else the ECM will have some confusion on when things need to be happening (canister purge, EGR, AIR diverter valve and TCC come to mind). IIRC, it should be 0.45v.

    No, the AIR Diverter valve won't cause drivability issues like that. Typically ti causes lean backfire on decel. This is due to an excessively lean mixture in the manifolds and it will be backfiring in them, not through the carb.

    It is very possible some vacuum hoses are misrouted. I would say that is #1 problem. Most mechanics don't understand what is really going on, and easily mess them up. Once you understand them, you can take almost any car and do the vacuum hoses without a chart with 80% confidence.

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