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'86 Chevy "put-puts"

Discussion in 'Chevy Trucks' started by whwright, Jul 16, 2003.

  1. whwright

    whwright Member
    Messages: 39

    I recently bought a 1986 C-10 with the 305 and quadrajet. The odometer says about 75k miles, and the truck is very clean so I don't think the odometer has rolled. I'm the fourth owner, and the title says "mileage exempt" so I can't be sure about the mileage.

    The truck broke down on the previous owner about a year ago, and has been sitting in his field. He told me he quit driving it when it developed a knock and had no oil pressure. Two bolts on the left exhaust manifold fixed the "knock," and a new pressure sending unit fixed the "oil pressure problem."

    Since taking the truck home, I have changed the oil, changed the belts and hoses, flushed the cooling system, rebuilt the carburetor, replaced the plugs and wires, and replaced the cap and rotor. I have also replaced lots of vacuum lines as I stumble across lines that have deteriorated (what a rat's nest!).

    The truck also had a propane system on it that didn't have a tank. The previous owner had sold the propane system to someone else, so I took it off and returned it to him. I don't know how much the truck was operated on propane, but I am assuming that it was quite a bit.

    Needless to say, the truck runs a LOT better now.

    However, when you rev the engine and take your foot off the gas, the engine "put-puts" out the tailpipe as it is slowing back to idle. If you hold the engine at 2000 rpm or so (it doesn't have a tach, and I haven't hooked up my dwell meter), it also "put-puts." The engine runs smoothly otherwise, and I haven't heard it "put-putting" as I am driving.

    I noticed at O'Reilly Auto they have an item listed called a "deceleration valve." Could this have something to do with this?

    Could it have something to do with the engine running on propane for so long? What are the long term effects of propane operation?

    Thanks for any help you can give me.

    Wayne.
     
  2. wyldman

    wyldman Member
    Messages: 3,265

    Start by checking the timing,or look for a propane timing computer.Propane needs huge amounts of advance to make good power,and the excessive advance may be your problem.

    BTW Welcome to Plowsite. :waving:
     
  3. whwright

    whwright Member
    Messages: 39

    Thanks Wyldman! I've been reading the posts on this board for about a month now, and your knowledge seems impressive.

    I didn't realize that the timing is set differently for propane. I'll check that out and get back to you if that isn't the problem.

    Wayne.
     
  4. wyldman

    wyldman Member
    Messages: 3,265

    Why thank you.

    I'm sure we can get to the bottom of you problem.Let us know how you make out.
     
  5. whwright

    whwright Member
    Messages: 39

    Hey Wyldman. The timing looks to be "OK."

    I found in my Chilton's manual that it says a "deceleration valve" might cause this problem. Well, I can't find a deceleration valve at any of the local parts stores, and I wanted to see what one looks like before I buy it to be sure that I actually have one.

    I sent a message to Borg-Warner tech support, and got this answer:

    So, what do you think of this response? How hard is it to diagnose the thermatic (sp?) air control system?

    We are leaving for the lake for a week, but I'll be looking forward to your response with baited breath (no pun intended).

    Thanks.

    Wayne.
     
  6. wyldman

    wyldman Member
    Messages: 3,265

    You said "the timing looks OK".Did you actually check it ? was the vacuum advance disconnected,and the truck idling ? and what was it at ?

    It could also be a sticky or siezed centrifugal advance.Pop the cap off and check to make sure the rotor moves freely back and forth a bit.It should move one way,and then spring back when you release it.If not,pop the rotor off and free it up.

    Also take it for a test drive with the vacuum advance disconnected,and see if it makes a difference.

    Does you truck actually have air injection ? If it does,you can disconnect the vacuum source to the divertor valves,so it just dumps to atmosphere,and take it for a drive.

    Also double check that the choke and heat riser system (valve on exhaust,and one on the air cleaner),are opening fully when hot.

    As a last resort,you can unplug all the vacuum lines and plug them up,to see if it helps.If it does,then you may have the vacuum system hooked up incorrectly.
     
  7. snowjoker

    snowjoker Senior Member
    Messages: 283

    Could it possibly be the Quadrajunk? I never had any luck with those things i know you said it was rebuilt maybe an adjustment is off ? Keep us posted
     
  8. wyldman

    wyldman Member
    Messages: 3,265

    The Quadrajet is actually an excellent carb.Best carb for all round power,drivability and economy.They have a very sensitive secondary metering system,and don't tend to "overcarb",like a Holley or others.

    There are many carb adjustments,even a few which aren't really for the do it yourselfer,which could be out.The throttle shaft bushings tend to go,and it leaks air,which makes them perform poorly.

    Did you rebuild the carb yourself ? If so then Walt may be right in the carb being suspect.Start with the basics first,and then if necessary,get into the carb.
     
  9. CARDOCTOR

    CARDOCTOR PlowSite.com Addict
    Messages: 1,310

    i beleive they call the part
    diverter valve
    attached to the back of the airpump



    cardoctor:alien:
     
  10. wyldman

    wyldman Member
    Messages: 3,265

    Any updates on the truck ?
     
  11. whwright

    whwright Member
    Messages: 39

    Funny you should ask...

    After cleaning up my father-in-law's van and boat, I finally had time to look into the "put-putting" some more.

    The timing is set at 4 degrees BTDC with the vacuum advance pulled and plugged, idling at 550 RPM. When you plug the vacuum advance back in, the mark jumps off the scale, and the idle goes up to about 800 RPM. When you put the truck in "drive," the idle pulls back down to about 550 RPM. I did not check the timing with it in "drive."

    I pulled the distributor cap (again) and checked the centrifugal advance. It isn't stuck. However, it must have fairly heavy springs because with the vacuum advance pulled, I never saw the timing budge between idle and 1500 RPM.

    I took the truck for a short drive with the vacuum advance pulled, and it didn't seem to make much difference. You may recall that I haven't heard the truck "put-putting" while driving, only when revving the engine in the driveway. With the vacuum advance pulled, it still made the strange sound in the driveway.

    I pulled and plugged the vacuum lines to the diverter valve and the decel valve, and it didn't make any difference.

    As best as I can tell, the early evaporation valve in the right exhaust manifold is open with the engine hot. I haven't ever seen the valve move, but I haven't owned the truck when it was below eighty degrees or so. The heat riser valve isn't hooked up. There was no air cleaner when I got the truck because it had the propane system on it. I got an air cleaner off an '85 model with a 350 at "Pull-A-Part." It fits, but I haven't taken the time to figure out how to hook up the vacuum lines. I did hook up the PCV vent, however.

    I have checked the vacuum routing against the diagram on the radiator support, and they appear to at least be close. The lines that go to the air cleaner were simply removed and plugged. I haven't spent the time and money to buy a factory shop manual yet; maybe when I get one I can figure out the vacuum routing with some certainty.

    I took the "quadrabog" apart and put a rebuild kit in it myself. When I got it, the truck had been running on propane so long the carb had a lot of brown stuff in it, and the accelerator pump was practically worn away. After the rebuild it runs infinitely better, but it still has a bog when you take off.

    I drove the truck to work today, and took one of the guys at the office to lunch in it (what a treat!). I hadn't even discussed the troubles I've been having, but Larry spontaneously said "hey -- it sounds like your cat is clogged." Could this be a possibility? How do you check such a thing?

    Sorry this got so long, but I tend to be verbose.:sleeping:

    Besides, I keep getting in trouble for not giving you enough information.:salute:

    Thanks for all the help.
     
  12. wyldman

    wyldman Member
    Messages: 3,265

    If the cat was plugged you would notice a large power loss.Those older pellet style convertors can't really clog or plug up anyways.

    Your heat riser valve on the pass manifold may be siezed closed.It wouldn't hurt to check it closely to make sure it's open.

    Try bumping up the timing some to 12-14,and leave the vacuum advance disconnected for the moment.See if it makes a difference and report back.Just curious to see what it does.

    The vacuum for the air cleaner goes from manifold vaccum (usually a tee right behind carb in manifold),to the thermoswitch in the air cleaner,and the from there to the vaccum door in the snorkle.
     
  13. chevy

    chevy Member
    Messages: 33

    I been toying with my Chevy for sometime now and had a simular problem. I check pretty much everyone said in this post and then some. My problem was a bad lifter which eventually burned a valve. After a good head job and up grade to a better cam my problem was solved. Good luck:)
     
  14. whwright

    whwright Member
    Messages: 39

    Hey Wyldman.

    I checked the heat riser valve, and it moves freely and springs back to the position its always been in. I believe that means it's "open."

    I was going to move the timing like you suggested, and while I was at it I thought I would reconnect the vacuum door in the snorkel. While searching for the correct spot to connect it in, I discovered that a screw-in vacuum fitting behind the carburetor was VERY loose. I couldn't get it to tighten up, so I took it out. I found it interesting, so I took a picture of it.

    I have no idea how the fitting got that messed up. It wouldn't seal to the intake, so I found a similar fitting from another old project and put it in. The truck appears to run better now, but the real story will be told when I drive it to work tomorrow. It still makes the strange sound, but it isn't as noticeable.

    At idle I now have 16 inches of vacuum at the manifold, which I think is pretty good, isn't it? The vacuum is also very steady, so I don't think I have a burned valve or anything like that.

    If it still runs funny I'll try the vacuum advance idea tomorrow night.

    Thanks for all the help. How do you find time for profitable ventures?

    Wayne.

    vacuum fitting.jpg
     
  15. wyldman

    wyldman Member
    Messages: 3,265

    Looks like maybe someone butchered that at one time.A large vacuum leak would make it run terrible.

    16 Hg of vacuum is OK at idle.If you did have a burnt valve,you would see that gauge bouncing around when that cylinder fires.

    I find plenty of time for profitable ventures during the day.Most of the time I spend on here,I'm sitting at my desk doing paperwork,and overseeing the auto repair shop.Snow is very profitable for us in the winter as well.I will have a bit more free time this winter,as I sold off a large number of contracts and equipment.I need a bit of a break.I'm getting too old for these 18 hr days,and never get to see the kids as much as I'd like to.

    I'm glad I could help,let me know if it's fixed.
     
  16. whwright

    whwright Member
    Messages: 39

    Well, I'm still not out of the woods yet.

    When I got going this morning, the engine started clattering when it warmed up. It was not like the usual acceleration clattering I'm accustomed to.

    When sitting at a stop light in gear, it would clatter. When I put it in neutral, the clatter would go away. When I took off, it would hesitate a little, rattle a little louder for about a half-second, and then take off. When the truck was moving I didn't hear it clatter at all, only when sitting still and then just off idle.

    After my first appointment I pulled the line off the vacuum advance. I neglected to bring anything with me to plug it with, so I just left it off (it's a little bitty line anyway). The truck stopped the clattering stuff at idle, but I still heard it a couple times when I just put my foot on the gas. There was also still a little bit of hesitation. The timing is set at 4 degrees BTDC, so I can't imagine it being too far advanced.

    My wife keeps telling me to just throw in the towel and put another engine in the truck (I have a Pontiac 400 on a stand in the garage -- wouldn't THAT be an interesting combo!). I still feel certain that there is something fairly simple that someone did to it, or something simple that has been neglected.

    Is it possible that the pistons have carbon buildup on them? Does running propane tend to create carbon?

    Thanks.

    Wayne.
     
  17. wyldman

    wyldman Member
    Messages: 3,265

    I doubt it's carbon buildup,as propane engines run very hot and very clean,so little or no carbon builds up.

    The Pontiac 400 would be interesting,but you'd need to fabricate mounts,and stuff.It would probebly be mork work than it's worth.

    Could you have checked the timing on the wrong cylinder ? #1 is the very front,drivers side.It does maybe sound like advanced timing.Maybe try to track down the rattle,and see where it's coming from.Maybe it's just something loose.Or maybe an internal engine noise ? Timing chain ?
     
  18. whwright

    whwright Member
    Messages: 39

    While I'm not looking at the engine right now, I'm pretty sure that I had the timing light clamped to the correct plug wire. If I was on the incorrect wire, it would have been #3, and with the firing order 1-8-4-3-6-5-7-2, I don't see how I could have been off by ninety degrees and still gotten the engine to run at all. The engine fires right up and idles great, which also implies the timing is closer than that.

    I'll look for a rattle, but why would something like the timing chain rattle with it in gear, but not out of gear?

    Earlier you mentioned that with a clogged cat the power will be way down. How much power should a 305 have? The truck won't even come close to breaking the rear tires loose (even my 200k mile '77 Cutlass will run off and leave it). If memory serves me correctly, the truck has 3.26 gears with 255/70R15 tires. I mentioned the lack of power to the "friend of a friend" who gave me the lead to find the truck parked in a field, and he stated that one of the reasons the truck was parked was that it had a hard time pulling the trailer that the previous owner needed the truck to pull. (The previous owner runs a lawn mowing service. That's kinda the Oklahoma equivalent of snow-plowing.)

    I'm still inclined to think there is something really simple that I am missing somewhere, and I'm close to being ready to declare "stumped." While it's a little embarrassing, my other cars are a '72 Mustang, '75 Grand Prix, '77 Cutlass, and '78 Trans Am (I also have a fleet of teenagers to go with this fleet of old cars). This truck has by far the most complicated emissions mess on it, and I'm just not acclimated to it yet.

    Do you have clients that are "stumped do-it-yourselfers" who bring vehicles to you for diagnosis? Do mechanics get ticked off when guys like me bring in a project like this to get help? Will I have to re-mortgage my house to pay the bill?
     
  19. whwright

    whwright Member
    Messages: 39

    [I don't have a clue why this post doubled up. The system wouldn't give me permission to delete the second one.]

    While I'm not looking at the engine right now, I'm pretty sure that I had the timing light clamped to the correct plug wire. If I was on the incorrect wire, it would have been #3, and with the firing order 1-8-4-3-6-5-7-2, I don't see how I could have been off by ninety degrees and still gotten the engine to run at all. The engine fires right up and idles great, which also implies the timing is closer than that.

    I'll look for a rattle, but why would something like the timing chain rattle with it in gear, but not out of gear?

    Earlier you mentioned that with a clogged cat the power will be way down. How much power should a 305 have? The truck won't even come close to breaking the rear tires loose (even my 200k mile '77 Cutlass will run off and leave it). If memory serves me correctly, the truck has 3.26 gears with 255/70R15 tires. I mentioned the lack of power to the "friend of a friend" who gave me the lead to find the truck parked in a field, and he stated that one of the reasons the truck was parked was that it had a hard time pulling the trailer that the previous owner needed the truck to pull. (The previous owner runs a lawn mowing service. That's kinda the Oklahoma equivalent of snow-plowing.)

    I'm still inclined to think there is something really simple that I am missing somewhere, and I'm close to being ready to declare "stumped." While it's a little embarrassing, my other cars are a '72 Mustang, '75 Grand Prix, '77 Cutlass, and '78 Trans Am (I also have a fleet of teenagers to go with this fleet of old cars). This truck has by far the most complicated emissions mess on it, and I'm just not acclimated to it yet.

    Do you have clients that are "stumped do-it-yourselfers" who bring vehicles to you for diagnosis? Do mechanics get ticked off when guys like me bring in a project like this to get help? Will I have to re-mortgage my house to pay the bill?
     
  20. wyldman

    wyldman Member
    Messages: 3,265

    OK,it sounds like the timing is pretty close then.

    When you put the truck in gear,the engine loads up,and will tend to shake a bit more,which could cause something loose to rattle.The timing chain would tend to rattle more in gear,or when the throttle is snapped open or closed.

    There is also the possibility it could be valve,or lifter noise.Does it sounds like that ?

    Have you tried disconnecting the EGR ?

    Another thought could be a camshaft.GM had a lot of problems with 305 cams,and maybe you have a lobe gone.This would cause little backfires sometimes,and a lack of power.

    The 305,with 3.26 (should be 3.23 actually),and the tall tires won't be very quick.It should still run pretty well though.

    I'd go back to basics.Disconnect everything,bump the timing up to 10-12 degrees BTDC,and see how it runs.No egr,no vacuum advance,nothing.Plug up all vacuum lines.If the problem is still there,then I'd pull the rocker covers,and make sure all the rockers are moving well.You would see if one was moving less,and the cam was bad.Before you put it back together,set the valves.See procedure below.

    Set the engine a TDC #1,then adjust the following:

    Cyls 1,3,4,8 exhaust valves
    Cyls 1,2,5,7 intake valves

    Turn the engine one full turn to TDC #6,and adjust the following:

    Cyls 2,5,6,7 exhaust valves
    Cyls 3,4,6,8 intake valves.

    To set each valve,loosen the nut until the push rod is free.Run it back down until all lash is removed,and then go 1 full turn more.

    While doing all this,watch the distributor rotor while you turn the crank back and forth.If the rotor takes a long time to move after the crank starts to turn,the timing chain may be badly stretched,or even jumped.

    See how it runs after that.Wouldn't hurt to check compression as well.Then after all this you know if the engine is sound or not.If it still acts up,then it must be something else,like carb,or ignition.

    You could take it to a mechanic,but he may not want to even bother after all you've done.I would take it on,but depending on how much time I spent checking and verifying everything,the bill could be quite large.

    If your content tinkering on your own,with a little of my help,I'm sure we can walk through it,and find the cause of your problem.Check everything I suggested so we know if the engine is even worth working on.If it will help,you could call me at the shop,and maybe I could walk you through some of it on the phone (9-6 Eastern time).It's easier that way sometimes.

    Number is on my website,under contact us. www.autoproformance.com