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"But how do it know?"
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Discussion Starter · #1 ·
Hi All,


I have a 1977 Chevy truck with a stock crate 350 engine and a 3-speed auto transmission. It seems to be suffering from power loss when in Drive. I drove the truck yesterday to move for the street sweeper and it gave no trouble.


This morning, the truck started up just fine, but when put into Drive, it had a serious loss in power. At first I thought it hadn't warmed up right and gave it more gas but it was more of the same. So I pulled over, shifted into Park, and gave it some gas. The engine revved smoothly with no issues.


So I shifted back into Drive and started driving and still no power. For reference, it was getting to 25 mph in over 10 seconds and there was no chance at going over 35 mph. It also was making a bhup-bhup-bhup noise. I tried shifting manually but that was of no use either.


I haven't had a chance to pop the hood and look at anything, but could it possibly be that the vacuum line to the transmission has come loose?


Thanks in advance, :thumbup:
 

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"But how do it know?"
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Discussion Starter · #2 · (Edited)
I just took a quick break at work to see if it was the vacuum line to the transmission that may have popped out. The hose seemed fine and in place.


I then started the truck and revved it. It hesitated - bogged? - and didn't want go beyond 2000 rpm.


I then reversed the truck a few feet and then drove forward again to see how it did. It exhibited the same hesitation as earlier.


Could it be a stuck/sticky choke plate?


I'm at work for another few hours and might be able to step out for a few minutes to tinker with it. If this seems like a quick fix and you guys can give me any hints, it would be greatly appreciated. Thanks! :D
 

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Does it have a cat on it? Check your tailpipe for obstructions. Almost sounds like a bad cat, maybe something has broke loose in it and has plugged off the exhaust.
 

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Discussion Starter · #4 ·
Hi crussell,

No, the truck doesn't have any cats. Its got two mufflers that are well-hidden under the bed. My first thought was the same as yours, but I didn't think much of much of it.
 

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do a spark plug check like I suggested to hauss in the other thread, look for abnormaly clean plugs, or at leas different collor from the rest, it may be just one or two adjacent plugs.

also find someone who has a exhaust gas analyzer and ask him to connect the probe over the radiator filling neck (do not inmerse in water) just slip a piece of old radiator hose over the neck to form a sleeve and stick the probe in it, if the analyzer detects any of the exhaust gases coming out of the radiator then you'll know you're in trouble.
 

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do a spark plug check like I suggested to hauss in the other thread, look for abnormaly clean plugs, or at least a different color from the rest, it may be just one or two adjacent plugs.

also find someone who has a exhaust gas analyzer and ask him to connect the probe over the radiator filling neck (do not inmerse in water) just slip a piece of old radiator hose over the neck to form a sleeve and stick the probe in it, with the engine running, if the analyzer detects any of the exhaust gases coming out of the radiator then you'll know you're in trouble.
 

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"But how do it know?"
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Discussion Starter · #7 ·
Hey Augusto,

I still think it is the vacuum hose going from the intake manifold to the transmission. It had slipped off before and the truck ran crappy until I put it back on. Here is how it looks now. Sorry for the low quality picture as it dark outside. How does it look?

I will try to check it out everything else tomorrow and report back.

 

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"But how do it know?"
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Discussion Starter · #8 ·
Checked a few things on the truck today. I began with the vacuum hose from the intake manifold to the transmission, and it seemed fine. I then removed the air filter assembly and visually checked out the carburetor and noticed that one of the vacuum inlets had nothing over it. I covered that with a cap.


I started the truck up a little while ago, let it warm up and took it for a spin. More of the same. It revs just fine in Park and neutral but sputters in every forward gear. Reverse gear seems fine, however.


When in Drive, the truck moves just fine for the first few hundred rpm and then begins ti falter. It will keep going but as more gas is given, the more it seems to lose power. This happens in every forward gear.


I also noticed that about two minutes after I turned the truck off, there was just the slightest white smoke comes out from the passenger-side rear on the engine area. I had the hood open during that time. I also noticed that the choke plate seemed to be stuck in one and place and I loosened it with a smack of a screw driver.


Augusto, I will be checking the spark plugs as soon as the truck cools down a bit. I unfortunately don't know anyone with an exhaust gas analyzer.
 

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Discussion Starter · #9 ·
Today, I began by checking the spark plugs. I pulled them all out, inspected them, wiped them down with a shop towel, looked 'em over again, and then cleaned 'em up using a wire brush and some carb cleaner. I did not see any color difference on any of them. See pictures at the end.


Another thing I noticed was what I believe is called the fast idle cam was quite stiff and would get stuck when being pushed back up by hand. With some far more than normal effort, it would finally go all the way up. I am not sure if that was a culprit in any way. See picture below.





My neighbor suggested checked out the ignition control module and the coil. I took them over to Autozone and had the ICM inspected. It passed twice. I noticed that there was no heat-sink compound beneath the ICM and this Autozone, it turns out, doesn't carry it. The employee helping me suggested using di-eletric grease. I wasn't able to get the coil tested because no one knew how.


I came home and looked up how to test the coil and cam across this thread: "Testing HEI Coil/Module". Doc Vette (RIP) provided the instruction on how to test out the coil in cap. The problem was, none of my two voltmeters were resetting to zero, and kept showing "1".


I then took the coil to Autozone and borrowed their voltmeter. The primary kept showing about 0.5 ohms. I could not get a reading for the secondary. However, when I took one prong to the rotor button and the other prong to the ground pin, which gave a reading of about 12.39 ohms. The employee looked up my info and it turned out the the coil was still under warranty. He swapped it out for a new one (Duralast brand), which I installed in the cap on the spot and then tested it out. The results were the same: about 0.5 ohms for primary, no reading for the secondary, and about 12.39 ohms when connected to the rotor button and the ground. I do not know what to make of this information and have decided to order another coil, probably from Summit, and return the Duralast one under warranty. Any recommendations on brands are very much welcome.


I came home, and reinstalled everything. The truck would crank but would not start. I figured the new coil was bad. However, I had struggled with plugging the battery wire to the coil, and decided to check to see if I had mixed up the battery and tachometer wires. After looking at pictures from a previous repair, it turned out I had mixed up the wires. I then swapped the wires into their correct places.


The truck then started up perfectly. i let it warm up for a few minutes and then took it for a spin. The transmission shifted smoothly. No hesitation, sputtering or bogging.


While I am glad the truck is back up and running, I still am not sure what exactly went wrong.


Thank you Crussel and Augusto for the help! :thumbup:




 

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Is it just me, or do the "even" plugs look to be badly oil fouled? If so, I would be looking at intake gasket sealing on that side....
 

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Discussion Starter · #12 ·
Hey sbchev,
sbchevfreak said:
Is it just me, or do the "even" plugs look to be badly oil fouled? If so, I would be looking at intake gasket sealing on that side....
Yeah, you're right. They are worse on the other side. I just replaced the gasket a few months back.




Hey SSedan,
SSedan64 said:
They do look oil fouled and the Spark Gap looks "HUGE" :confused: What are you gapping your Plugs at?
They are gapped at 0.60", which is what the gap is for the California models. However, when I first did a tune up after the buying the truck, the spark plugs that were already in the truck were gapped at about 0.50". Should I try for a smaller gap?


Also, I mentioned in a earlier post that I saw slight white smoke coming out of the passenger-side of the truck a few days back. It occurred a couple of minutes after I turned it off. Could that be related to the spark plug fouling issue?




Thanks for the continued help! :thumbup:
 

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Lower compression smog engines do have some Wide Gaps, if it's stock .050"--.060" is probably correct.
Friend of mines Mom had an 85 Gutlass 307ci that had .080" plug Gap listed. :eek:
White smoke :confused: I'm not sure what that could be. Something burning or steam :confused: :pain:
 

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Discussion Starter · #15 ·
This morning, I started the truck to move it up the drive way for the street sweeper. It started up fine and reversed up the drive way with no issues.


After the sweeper passed, I drove it back down the drive way under its own power, without giving it any gas. Once onto the street, I gave it some gas and it started stumbling again. I put it in Park and revved the engine. I hesitated slightly around 3,000 rpm. I then slowly drove it in Forward and Reverse along the side walk several times. It would stumble in Forward, but no issues in Reverse.


I put it back in Park, revved the engine close to 4,000 rpm, and it did so with no issues. It began idling at around 1,000 rpm, vs 750 rpm initially. I then drove the truck up and down the street and it drove and shifted like normal: a little hard in 1-2, and then somewhat hard in 2-3.


I am still at a loss as to what is going on. It almost sounds as if revving the engine cleared up something fuel related. Any ideas?



EDIT: Gonna check the clear fuel filters first chance I get to see if the fuel is crap (again). Hopefully no later than tomorrow.
 

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Discussion Starter · #16 ·
This sounds like an odd question, at least to myself, but I have been wondering if a bad or failing ignition component such as the distributor, ICM, or the coil can act up or show symptoms of failure during certain temperature conditions.


I have been running the truck without a thermostat while doing the cooling system flush. I don't drive it and it rarely gets over 160 degrees. Should be completing the suggested 3-6 hour "flush run"this weekend. I will be replacing all hoses and putting in a new thermostat at that time.
 

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Discussion Starter · #17 ·
Today, I repeated what I did yesterday. I started the truck, let it warm up for a few minutes, then revved the engine while in Park. The engine bogged and didn't want go beyond 2000 rpm. I moved it back and forth slowly while near the curb, put the transmission back into Park, and revved it again. Same result.


I then let the engine idle while I looked under the hood. I noticed that the glass-cased fuel filter right before the carburetor seemed a bit dirty. The engine was idling just fine. The picture of the filter is below. Interestingly, the filter before this one, also a see-through, didn't appear dirty. the only picture I took of it came out unclear so I will post another one next time.


I then revved the engine again, all the way up to 4000 rpm, and it did just fine. I then drove it around and again, no issues. What is it that seems to go away after some idling and high-revving?


I am planning to complete the cooling system flush this weekend, at which point I will install a new thermostat and check and adjust the timing from there (thank you Pugsy).


On a side note, I am still wondering about the fast idle cam and how sticky it seems. Could that be the cause? Perhaps it "moves out of the way" after the engine has been revved hard enough. I will try do this again tomorrow, and video the carb to see what happens. First, clean out the filter, of course.


 

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how much is this truck driven? How fresh/old is the fuel in the tank? Maybe dump in some dry gas or something. Did you ever do a compression check to try and track down what caused the oil fouled spark plugs?
 

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Discussion Starter · #19 · (Edited)
crussell85 said:
how much is this truck driven? How fresh/old is the fuel in the tank? Maybe dump in some dry gas or something. Did you ever do a compression check to try and track down what caused the oil fouled spark plugs?
It usually wasn't driven much. Just warm it up once or twice a week and move it for the street sweeper. I've been using it a lot more frequently the past few weeks because of the change in job location. The gas in the tank shouldn't be more than a month and a half old, but I could be wrong.


I will be removing the filter and inspecting the contents some time this weekend. At the friendly nudging of another member, I will also do the timing as soon as I can set some time aside for it (no pun intended), hopefully this weekend.


Also, another thing I've come to notice about the truck recently is that after it is started and/or driven, it doesn't always start back up right away. The lights and everything come on but the engine doesn't turn over. What I end up doing is shifting the transmission all the way up and down the column and then trying again. This always seems to fix the problem. This does not happen on cold starting.


Thank you for the continued help! :thumbup:
 

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cooling system has nothing to do with this problem

the symptoms lead to a clogged exhaust or a clogged carburator

also a bad fuel pump can do the same

if there are no backfires or the engine keeps running after the ignition is cut, I would say the ignition sustem is fine, but I'll look anyway under the distribuitor rotor for a frozen timing advance mechanism.

does it smoke black when the problem happens? this will lead you to an overly rich clue, like a choke plate that shuts or a bad needle valve.
 
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