99ls1ta

Sorry for long post. I bought a 1987 Cadillac Brougham last year that was in storage for over 10 years, all original 89,000 miles. It is a car with family history so id like to get it running right. It started and ran okish with fresh battery oil, and fuel but had a stumble at low throttle input, exhaust smelled rich, and a check engine light. Had enough power for acceptable acceleration for what it is, get up to 70mph and could cruise there in overdrive converter locked. I changed the timing chain to get rid of the nylon teeth, replaced fuel pump and filter and after job completed on the test drive car ran the same but the intake manifold gasket started leaking out the front.

I took pictures of the vacuum line route and replaced the intake and carb gaskets. I put it all back together and it runs terrible. The first about 45 seconds it seems to be ok, slight stumble but reasonable idle speed, after the 45 seconds or so it gradually picks up idle speed and the exhaust smells very rich. If you try to drive it has barely enough power to hit 55 mph floored, the stumble at low input is much more noticeable, and it seems to have lost overdrive, converter lockup or both (probably why the stumble is more pronounced). I jumped the pins and got code 13,15,and 21. replaced the o2 and coolant sensors cleared the codes and now no check engine light but the car runs the same. Double checked the throttle and choke linkage for operation and obstruction, throttle operates fine, choke appears to be operating (seems to pick up rpm as it opens). Rechecked my vacuum line route and condition, and sprayed carb cleaner all along the intake manifold/head, block seams and carb mounting gasket, no change in engine speed.

I'm not very familiar with carbs so I'm lost at this point. I read on this forum that the MCV should click key on engine off, I hear one click sometimes when I first turn the key but one click only and not every time. Is it supposed to continue clicking or one and done? could that solenoid be sticking? or is there anything else that I should be looking at? Thanks for any and all help in advance.

joe_padavano

This uses the computer-controlled Qjet, known as the CCC system. It controls the distributor advance curve as well as the carb. You MUST follow the adjustment instructions in the Chassis Service Manual EXACTLY, or the car will never run right. You must also verify that not only are the vacuum hoses connected correctly but that all the related systems are functioning correctly. As an example, on one of my cars the check valve in the A.I.R. system failed open, which allowed hot exhaust to get into the diverter valve in the A.I.R. pump. This blew fresh air directly at the O2 sensor, so the computer thought the car was running extremely lean and ran the carb full rich as a result. This will not set a code on the MIL, since the OBD I system is extremely limited in computing power and number of sensors. Unfortunately few people knew how to properly adjust these cars when they were new, and pretty much no one does now. I had to learn myself. I've had five cars with the CCC system (three currently) and they work fine if adjusted correctly.

69HO43

Just to check and make sure since the car's been sitting forever...

Have you checked the choke pulloff? Front passenger corner. With the car not running and cold engine, pull the hose off the "T" and apply vacuum then lock down the vacuum. It should hold the choke partly open for like 10 seconds minimum. If it starts to allow the choke to close again and the plunger starts moving out before 10 seconds with vacuum applied and held, then the pulloff diaphragm is too far gone and needs replacing. It's also a source of a vacuum leak when the diaphragm is busted.

Code 13 is a puked out O2 sensor. Since you replaced that, you should be ok there.
Code 15 is a an open coolant sensor. This is the computer one, which you have two temp sensors next to each other. One next to the thermostat on the driver side, and one outboard driver front corner. The one on the outboard front corner is the ECM temp sensor for the computer. It doesn't care what the other sensor for your guages is doing. An open sensor makes the car think it's never warming up (high ohms/open means the computer thinks the coolant's -40 F). Which means you're likely getting stuck with a preset timing and mixture settings.
Code 21 is a Throttle Position sensor (TPS) high reading or open. This make the engine think the throttle is open way more than it should for the current idle speed or load condition, etc.

All of these could cause the problems you see. As well as the lock up converter not working. It won't lock up unless the car sees closed loop along with other parameters, like speed and gear position, etc., but if the car doesn't "see" closed loop, you won't have lock up.

99ls1ta

Yeah once I started flipping through the Brougham service manual I got I realized this is way worse than the LS stuff I'm used to and how spoiled I am on modern scan tools. If it wasn't for the fact this car is the one my grandfather ordered the day he retired, the memories I have with it, and its back in the family after 15 years I wouldn't have bothered with it.

I'll check the choke pull off when I get home from work. I also picked up a vacuum gauge so hopefully I can test for leaks in the vacuum lines and I'm trying to track down a dwell meter though not 100% sure on how that works on these cars. I replaced the coolant sensor with two wires going to it, pretty sure it was the outboard one and no longer have the code 15 and strangely no more 21 either.

The AIR pump is shot and no belt running it but never did since I owned it so I ruled it out as a cause of the problem. I remember lots of cars with smog pumps disconnected when I was growing up so I ignored it. Is that a potential issue?

joe_padavano

If you still have a cat, the air pump is needed to blow cool air into the catalyst or it can melt down.

69HO43

Cat won't work as efficiently without the AIR system. AIR system added extra oxygen to the exhaust system to help burn the unburnt fuel and in the catalytic converter, which you have a dual bed, helped the 2nd stage of the cat converter reduce hydrocarbons and carbon monoxide. The first stage took care of NOx. It wasn't active 100% of the time but if the check valves leaked, exhaust gases came back into the AIR system which sucks because it start melting the plastic junk and mucks up the AIR pump. Of course, as mentioned, a malfunctioning AIR system won't throw any codes since the computer doesn't "see" it.

Sugar Bear

I'm guessing you are looking for a dwell meter to check/adjust the mixture control solenoid, if you find one set it to 30 degrees on the six cylinder scale OR use a duty cycle meter and adjust it to a 50% duty cycle.

69HO43

There's a little green connector in front of the carburetor that's not connected to anything. That's the dwell meter connection. You may could do it with a digital meter, but the fluctuations will drive you crazy. Analog dwell meter is best.

If you have some time to kill, here's some OLD GM CCC videos below that helps explain some stuff about the CCC system. Spend some time with these and it will make things a bit more clear as to things you can do and check. The CCC system was an ever-growing process. They didn't stand still while developing it over the years so some things over the years have changed a bit, but the principles are pretty much the same. The narrator is monotonous, but it's typical training video narration.

69HO43

V6 or V8, always use the V6 scale because it makes the dwell reading more centered when you're at 30. Some dwell meters have separate scales on the face to make it even easier.

For example, in the picture below, note the dwell reading goes all the way to 90 degrees. That's for 4 cylinders. 90 deg x 4 (number of cyl) = 360, or full circle. So if you flip the switch to the 4 cylinder mode, you just read it off the scale. The 6 cylinder scale uses 0-60, (60 x 6 = 360), and the 8 cylinder scale would use 0-45 (45 x 8 = 360). It's much easier to use 30 degrees as the mid point (50% duty cycle), so that's where GM wants you to set the scale provided your meter has a 6 cyl scale. Anything under 30 is rich, over 30 is leaner. You never get a super steady reading like it's locked in, but it will vary a bit but "hang around" 30 degrees for optimum setting. But with a single 90 degree scale, if it was in 6 cyl mode, you would divide by 1.5 degrees for every degree on the 90 scale. So in this instance on this particular meter, with a single 0-90 scale, you would want to use 45 degrees as your mid point and set on 6 cyl 45/1.5 = 30. It's really not a huge deal, as long as you find the mid-point and use that for setting the carb's mixture control solenoid duty cycles. Hopefully all that made sense.

You can find analog dwell meters on ebay for cheap. This one is 10 opening bid (currently 0 bids) and 10 for shipping. Not much need for analog meters today. Saw a Sun dwell meter on there for around 90 shipped. Just depends on what you want to spend. For as much as you'd likely use one, you don't want to spend a lot of cash on one. I have an old Sears engine analyzer that still works well. I also have a Brainmaster II that's digital but heckuva lot more useful.


Here's a short video of someone running the 6 cyl scale dwell meter to the green test plug while dialing in their readings by adjusting the idle air bleed valve. Note the eventual sweep slightly above and below 30 as it gets dialed in. This is what you're looking for. Something like this.

Dynoking

Pro tip
The primary metering rod spring was known to break. No amount of external adjustment will help if either spring is broken. The biggest problem I remember is the spring(s) break. Then attempts to correct the resulting drivability problems are made by removing the adjustment seals and turning the adjustment screws. Now you how a carb that has broken primary metering rod springs and is hopelessly out of adjustment. I always cringed when I had a GM vehicle with drivability issues and the seals on the carb were removed.

https://quadrajetparts.com/quadrajet...ngs-p-211.html

joe_padavano

OK, but if the springs go bad, the metering rods drop down in the jets and the car runs lean. His car is running rich.

jcdynamic88

i have seen a bad purge valve raise havoc on these engines ,the large rubber hose that connects to the top front of the carb shouldn't have any fuel in it,if it does the valve is bad

joe_padavano

There are about a bazillion potential failures that can cause the CCC system to go sideways. Shotgunning new parts onto the engine is a great way to spend a lot of time and money to not fix the problem, and frequently it can introduce new, creative failure modes. Diagnosis following the factory Chassis Service Manual is the best way to solve this problem.

69HO43

Truer words were never spoken.

The most beneficial thing you can do is to get a specific chassis service manual (CSM) for YOUR car. Albeit you can find some incomplete or incorrect information in them on few occasions, it's rare.

EDIT: Never mind, I missed where you already have a service manual.

69HO43

I've seen carbon particles in that valve and hoses as well when the upper membrane in the vapor canistor failed and the engine sucked the tiny little carbon chunks up through the lines. No external indications of a problem. The TCV that helps in that system also can go bad or comes apart, so yet another can of worms. But a purge valve is quick to check the diaphragm too. Just apply some vacuum and hold it and if it leaks, you'll know it in a hurry.

If anyone thinks that bowl vent leaks won't hurt carburetor performance on a CCC system, think again. If anything messes with the fuel bowl pressure, it can cause fuel/air mixture problems. A vacuum leak on the purge valve could upset that pressure balance and cause mystery issues. Again, not a straight line problem to be solved. ANY non-designed vacuum leak on a CCC system is bad.