The "boggy" Monte Carlo

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The "boggy" Monte Carlo

Post by Wildcat445 on Sun Jan 31, 2016 1:23 pm

Our next-door neighbor here is one of those neighbors that only come along once in a lifetime. He watches our place like a pitbull when we are not here. His wife makes us fresh tamales and chorizo all the time. Just a good couple.

Their grandson from California was visiting the other day. He has an early 1980's Monte Carlo with a 305 V-8 and all the goodies that he has fixed up. It has all the kid toys, including having the trunk filled with speakers. The thing thumps so hard I can hear him coming five miles down the road.

The Monte started running poorly. It had really low power at times. Going down the road, it acted like someone had "dropped the anchor". The young man took the car to a local shop and they did all kinds of work to it, rebuilt the carburetor, EGR valve, a full tune-up. Almost $1200 worth of work, all to no avail. Absolutely no improvement, and, perhaps maybe worse than before. The kid came over when I was cleaning my car and asked me what I thought. I decided that a test drive was in order. We took off with Kanye West rattling the windows. The thing ran like a skateboard. 305 Chevrolet engines are not known as being drag race engines, but it should run better than it was. I noticed something strange. In between "tracks" when the "music" was not playing, the power increased. I had an idea. I had heard of this before, but it had been a long time.

I asked if I could drive. The young man agreed, so I took the wheel. I asked that the music be turned completely off, so I could "hear" better. The car ran like it should. I could run thru the gears manually and it would get scratch. The kid started to grin and asked me "what did you do?" I asked that he turn the "music" back on. When it came back on, the car acted like it ran into a brick wall. No power whatsoever. When the music was off, the car ran fine. Music on, the car ran like crap. It did not miss, it just had no power. Would anybody care to take a guess at what I found?

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Re: The "boggy" Monte Carlo

Post by Conelrad on Sun Jan 31, 2016 2:09 pm

The mega-amp draw from the music system pulled the ignition voltage too low?

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Re: The "boggy" Monte Carlo

Post by Tony V on Sun Jan 31, 2016 3:15 pm

I'm with Conelrad. Putting a high amp alternator in it might improve or cure the loss of power. The computer in these require at least 11 to 12 volts minimum to run right. A high amperage alternator should keep it at a rock solid 13 1/2 to 14 volts with everything turned on. I used to run into this problem alot with guys who had ham radio's set up in their cars. Every time they hit the mike to transmit it would all but kill the performance. Replacing the stock alternator with a high amperage one always did the trick. Make sure that the positive cable going to the amp is directly fed off the battery with a fusible link as they draw so much current they can fry a wiring harness if wired into it instead of the battery.
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Re: The "boggy" Monte Carlo

Post by Wildcat445 on Sun Jan 31, 2016 4:52 pm

Close, but not quite there.  Very Happy

This car, a 1983 model, was equipped with the GM CCC (Computer Command Control) system of computer controls.  It had a Quadra-Jet carburetor.  This early system of computer engine controls, actually worked fairly trouble-free for its day.  This particular engine (Code W) utilized a knock control sensor, located on the right side of the engine block, under the exhaust manifold, mounted in the hole where the drain petcock was located in the olden days.  It also had a MAP (Manifold Absolute Pressure) sensor, located on the firewall in the engine compartment.  These sensors measured certain engine performance perameters, among them them being the control of pre-ignition (knock).  These two sensors basically retarded ignition timing to eliminate knock.  This car had four 12" woofers in the trunk, powered by a bazillion watt amplifier.  The boom-boom of the woofers was strong enough to disturb the signal from the knock sensor and was on a frequency that disturbed the MAP sensor.  This, in conjunction with some pretty incompetent driveability work, conspired to produce a really sick 305 when the kid had the jams cranked.

Whoever performed the tune-up overlooked a couple basic systems that were notorious in the day for causing performance problems in GM vehicles.  Whenever I got one of these vehicles, basically 1978 to the end of the distributor days in for a performance complaint, the first thing I would do is to take a good look at the distributor and its components.  Distributor cap, rotor and especially the centrifugal advance.  On cars with over 10,000 miles, I could depend on the fact that 99% of the centrifugal advances would be stuck.  They would stick in the full-advance position.  A technician diagnosing a driveability complaint would note fast timing, retard it, then send the car down the road.  Any degradation in performance by the knock or MAP sensors would cause the driver to notice a drop in power.  This car suffered from this malady.  The static timing was set at -34 degrees, since the centrifugal and electronic spark advance typically would be 34 degrees BTDC at about 1200 rpm or so.  The timing on this particular engine was simply set 68 degrees slow!  

The fix, besides turning the music down somewhat, was to go to OReilly's and get a new distributor cap, rotor, ignition module and to free up the centrifugal advance.  I pulled the distributor, pulled the shaft apart, cleaned everything up well, lubed it with anti-seize and put everything back, then set the timing to spec, engine warm, etc.  I replaced the module with a genuine GM part, since my experience was that aftermarket stuff causes problems.  The kid can now run his jams at "22" on the volume control, which is pretty loud.  Any louder and he can still experience performance problems, since the knock sensor will only take so much.  The car actually runs pretty well for a 305.  It is on 3.36 gears, with a TH 700-4R transmission.  The kid learned something about his car, we had some fun working together on it, and I remembered something useful for a change.

As a side note, back in the day, late 1980's.  The California Highway Patrol ran a fleet of Fox-platform Ford Mustangs with the 5 Liter engine for pursuit vehicles.  Some wise trucker found that if one had a CB radio running a linear amp, you could shut down the CHIP Mustangs.  One would tune to a channel, 15 IIRC, key the mic with the amp on, and then blow the air horn.  This would send a signal strong enough to shut down a pursuing CHIP Mustang, by disturbing the frequency the sensor ran on.  The cops found that by wrapping the MAP sensors in aluminum foil would "foil" the plot.

The kid with the Monte Carlo has a 120 amp Delco SI alternator and a truck battery in the trunk to power the stereo system.


Last edited by Wildcat445 on Sun Jan 31, 2016 4:56 pm; edited 1 time in total

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Re: The "boggy" Monte Carlo

Post by Conelrad on Sun Jan 31, 2016 4:55 pm

Ergo, the benefit of a simple Diesel car...

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Re: The "boggy" Monte Carlo

Post by CrazyCanuck on Sun Jan 31, 2016 5:15 pm

One other problem that all 1980's GM 305's had was poor hardening of the cam lobes. Unless a mechanic knew about the problem, they could chase it for hours, change all sorts of parts and still not fix it. It was also a problem that showed up over a long period of time, so the owner would not be able to say just when the problems started.

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Re: The "boggy" Monte Carlo

Post by Wildcat445 on Sun Jan 31, 2016 5:29 pm

I may have to "tell" on myself before this is all said and done.  Rolling Eyes

When I had my auto repair shop, I had an old hand working for me named Frank who had been around since the Ford flathead days.  A more crothchety, cantankerous old fart never existed.  Frank may have been the best (next to my grandfather) auto mechanic I ever knew.  Frank could fix it, period.  Frank did not do cars newer than 1980, did not do foreign cars, hated Chrysler.  Frank knew GM stuff.  Frank was seldom wrong, never had a comeback.  He was slow as pond water.  One job a day, done very well, was his forte.  No other shop wanted Frank around, since he was so hard to get along with.  He was a teddy bear.  He got crotchety when somebody found that out!

I had a 1984 Buick Park Avenue with the infamous 5.0 (Y) motor in it in the shop.  An Oldsmobile 307 V-8.  Quite possibly the worst-performing engine GM ever built.  I remember it being rated at something like 120 horsepower and felt that was over-rated at times.  Ultra-smooth, dependable for those days.  Its main issues were a hundred feet of vacuum line that would frequently fail, leaky valve cover gaskets that required removing the vacuum lines to fix, and chronic performance complaints.  Mechanics hated these engines.  

The PA I was working on would barely run.  And not at all with the AC on.  It stalled.  The trans did not shift right.  It started hard, especially when warm.  It overheated.  The dealer was stumped.  Why the car was brought to my shop, I have no idea.  The car had a tad over 13,000 miles showing on the odometer.  

I drove the car into the shop.  Frank was working in the next bay.  "Goddamn timing is too slow" is all he would say.  Not that I had asked him.  He did not do "computer" cars.  He had not looked at this one, the hood was never up yet.  "Set the damned timing right.  Idiots!" was all he said.

Long story short, this was my first experience with a stuck centrifugal advance on a GM "computer" distributor.  Another long story short, 15 minutes of work and some WD-40, and resetting the timing correctly, made a different car of this Park Avenue.  I remember charging the customer $27.50 and wondered if it was too much.  I never forgot that.  How Frank knew timing was the issue, I have no idea to this day.  Frank passed due to cancer in 2006.  He willed me his tool box.  That was all he had he valued, his prize possession.

Now the "tell."  There was a GM TSB (Technical Service Bulletin) for GM CCC cars saying that wheel bearings, center carrier bearings, universal joints, unbalanced wheels or other "extraneous noises" could disrupt the knock sensor, possibly creating difficult to diagnose performance problems.  I can't speak for other mechanics, but I kept this incident with the Buick and the TSB in mind when dealing with intermittent performance problems in GM vehicles of this era.  The kid with the Monte Carlo caused me to remember this, and it worked out well.

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Re: The "boggy" Monte Carlo

Post by Wildcat445 on Sun Jan 31, 2016 5:51 pm

The comment about the soft camshafts is well-taken. One could typically find a flat camshaft with a good vacuum gauge. GM replaced millions under warranty and sold millions more replacement engines. Buick had cam issues in the straight 8 days. Pontiac and Oldsmobile had noisy lifters in the 1950's and '60's. I wondered at the time how a company as big as GM could have chronic lifter and camshaft issues for such a long period of time.

I had also wondered how many of the first "computer" cars were left on the road. This particular Monte was a California car, with California emission controls on it. Everything I could see was still connected and in good condition. It had a smog pump, had operating smog pump dump valve, the EGR was connected and all those vacuum lines were still there. I was amazed that anyone nowdays would and could work on that computer MV series Quadra-Jet. Who would still have the tools to set the rich-lean authority on the carb? Could you still get carb parts? Apparently you can. I'm not positive that this carb was set up right and did not have my tools to check it. It worked okay as far as I could tell.

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Re: The "boggy" Monte Carlo

Post by willy3486 on Mon Feb 01, 2016 2:15 pm

I was going to say his music was so bad even the car didn't want to hear it and it tried to cut itself off. Good to see you figured it out.

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Re: The "boggy" Monte Carlo

Post by Guest on Mon Feb 01, 2016 5:32 pm

Very interesting diagnosis! Very Happy

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Re: The "boggy" Monte Carlo

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