I know my truck is shot. I've been told one cylinder has no compression. The truck is a '78 Chevy 350-4 barrel with HD emissions. It has 320,000 miles. I've replaced the wires, plugs, rotor; distrib cap; rebuilt carb . When it starts, it is rough, but it runs until it warms up. Then when I come to a stop, it idles down and dies. If I'm quick enough, I can shift it into N and the engine idles up again. Little power upon acceleration. Once going, it'll go 80 mph. Seems like the timing is off, but I guess that is because of the lack of compression??
Since I'd rather not put a new engine in it and wind up probably having a new set of problems with the transmission, which basically acts OK, is there anything that I might have replaced that might give it a little longer life?
Wow, with that many miles I'd think it's a diesel. I think it's time for a new engine, maybe you can find a truck with fewer miles rusting on the side of the road and put the whole kit-n-caboodle in there (engine and tranny)
Run a compression test. If compression is down on one, two, three but NOT ALL of the cylinders, it's not timing. If compression is down on a few cylinders by more than 25 psi from the others, time for a rebuild.
If that's the only way to keep it running another 6 months, what is reasonable to pay for a rebuild? STP won't help? :-)
compression.
320,000
acceleration.
Run a compression test. If compression is down on one, two, three but NOT ALL of the cylinders, it's not timing. If compression is down on a few cylinders by more than 25 psi from the others, time for a rebuild.
If you've already got 320,000 miles out of this truck, it owes you nothing ;-)
Average lifespan before a rebuild of a 350 of that age is around
150,000-175,000 miles, and even THAT'S pushing it. Now if that
320,000 was all highway driving, you'd probably get more. Still, it's amazing that the truck still runs.
If the truck is in good shape and you plan on keeping it a long time, I'd look into having a crate motor put in it. This usually costs less than a total rebuild. If the transmission has never had a rebuild, I'd also look into one of those.
If it's a beater and you just want to keep it going, I'd find a junkyard motor/tranny combo and put in it.
Go simple first, a stuck EGR valve is a lot easier, simpler, cheaper to deal with than a stuck intake valve or bad cylinder compression mechanics and will manifest the exact symptoms you describe. So before you chunk the motor. Please check this first!!!
COLD ENGINE Start with removing the Vacuum line from the EGR valve and plug it off with your finger. Does the Idle smooth out? Do you feel vacuum against your finger. You should not feel a vacuum at an idle in the EGR vacuum line. Which means the EGR should not pass exhaust gas into the intake. If you do feel vacuum the motor idle may have smoothed out when you removed the line. Check the source of the vacuum. Gee wouldn't this be great if you found that you plumbed the EGR vacuum to a live manifold source. A cold motor with that many miles with a choke butterfly slammed shut would return enough un-burnt fuel back through the EGR to keep it running pretty good. Until the choke released of course. This would not be the first time a zero dollar fix cost
3 grand.
WARM ENGINE Remove the Vacuum line from the EGR valve and plug it off with your finger. Does the Idle smooth out? Do you feel vacuum against your finger. A road temp engine you should feel a small vacuum at an idle in the EGR vacuum line. Which means the EGR is passing some exhaust gas into the intake.
STUCK EGR Remove vacuum line from EGR and temporarily plug. Take vacuum from good source and apply to EGR valve. When vacuum is applied to an idle engine it should stall the engine. For your case you may need to use the fast idle choke cam or whatever to hold a slow as possible but steady RPM, then apply the live vacuum to the EGR valve. You should see a difference in RPM.
If the stuck EGR test has no tangible results then change the EGR valve and run the tests again.
The ERG valve is used to cool the Catalytic converter by replacing the intake atmospheric air with exhaust gas Which will richen mixture - less air during deceleration and hot idle and in turn very efficiently re-burns pollutants in the super heated converter. In your case what peaks my interest is your description of the runs fair cold (EGR is shutdown until converter temp comes up) then when the engine warms up (EGR system kicks in). Now the EGR system could just be aggravating poor mechanical compression. Which gets lengthy...
If the EGR has been ruled out then consider:
Find the bad cylinder, or get the expert to tell you which one it is. Then say "I'll run down to AutoZone and pick one up this weekend" (that's a joke by the way) and leave it at that.
a. Plug wire method. The engine may run better with the plug wire removed from the bad cylinder. Warning! do not drive a gasoline engine without spark plug fire for prolonged time due to contaminating the oil with raw fuel or if it runs a lot better you ma not care if the oil gets contaminated
b. Carefully examine each spark plug, and run compression test
Since you say that it stalls at idle you may have an intake valve that is not sealing during combustion. If it will do 80 is not a "bottom end" "swinging parts, crank, rods, pistons, melted pistons," problem. Melted pistons will cause loss of compression but the bottom end usually will not survive an 80 MPH run.
Lets get back to the intake valve and your cheap fix.
When an intake valve is stuck open the intake manifold vacuum is so low and contaminated the other cylinders cannot draw enough air/fuel charge at low RPM to run. Then the engine stalls.
How can an intake valve stick open or not properly seal?
Valve head worn, burnt or melted - requires removal of the head to repair Broken valve spring, valve springs return valves to the closed position - may be repairable without teardown Cracked Cylinder head - Teardown
What to do,
Leaky Intake Valve
- Pull the rocker arm cover
Try to determine if the valve is stuck
- Remove the rocker arm from the leaky valve
- Use the wooden handle end of a hammer and push on the valve stem with your hand on the head of the hammer, makes a good handle. It should be near impossible to move the valve without most of the energy you can muster up. A valve spring compression tool should do this quite easily but should bet met with skill and experience.
- OK so the valve moves a little with the hammer butt. Now compare to another valve. Don't be tempted to hit the valve stem with the hammer, If you knock out the retainers you will get a spring in your face.
- Time to remember this is on the cheap, no $100.00 bills, right?
- I have taken a cordless drill to a valve stem with lots of WD-40 sprayed down the stem and in the cylinder and rotated the valve very slowly, while spraying cleaner, to clean up a stem and seat. Can't get much of a cheaper try than that without a teardown.
Put the valve cover back on and only seal one side of the gasket. You will have to take it off again.
See if you have done any good, You may just want to run it without the cover in the driveway to shorten the test time. You should be able to tell pretty quick. While the cover is off check for slack in that rocker arm.
All else fails
- Pull the rocker arm cover again
- Remove the push rod and rocker from the leaky valve and leave them off
- Don't worry about the lifter, you or the cam couldn't eject it topside after 300,000+miles of crud anyway
- Up your oil viscosity to 20W50 below Interstate 70 (mid to southern states), 10W40 in northern winter climate. The higher viscosity will help push more oil topside buy increasing pressure to keep valves lubricated
Go simple first, a stuck EGR valve is a lot easier, simpler, cheaper to deal with than a stuck intake valve or bad cylinder compression mechanics and will manifest the exact symptoms you describe. So before you chunk the motor. Please check this first!!!
COLD ENGINE Start with removing the Vacuum line from the EGR valve and plug it off with your finger. Does the Idle smooth out? Do you feel vacuum against your finger. You should not feel a vacuum at an idle in the EGR vacuum line. Which means the EGR should not pass exhaust gas into the intake. If you do feel vacuum the motor idle may have smoothed out when you removed the line. Check the source of the vacuum. Gee wouldn't this be great if you found that you plumbed the EGR vacuum to a live manifold source. A cold motor with that many miles with a choke butterfly slammed shut would return enough un-burnt fuel back through the EGR to keep it running pretty good. Until the choke released of course. This would not be the first time a zero dollar fix cost
3 grand.
WARM ENGINE Remove the Vacuum line from the EGR valve and plug it off with your finger. Does the Idle smooth out? Do you feel vacuum against your finger. A road temp engine you should feel a small vacuum at an idle in the EGR vacuum line. Which means the EGR is passing some exhaust gas into the intake.
STUCK EGR Remove vacuum line from EGR and temporarily plug. Take vacuum from good source and apply to EGR valve. When vacuum is applied to an idle engine it should stall the engine. For your case you may need to use the fast idle choke cam or whatever to hold a slow as possible but steady RPM, then apply the live vacuum to the EGR valve. You should see a difference in RPM.
If the stuck EGR test has no tangible results then change the EGR valve and run the tests again.
The ERG valve is used to cool the Catalytic converter by replacing the intake atmospheric air with exhaust gas Which will richen mixture - less air during deceleration and hot idle and in turn very efficiently re-burns pollutants in the super heated converter. In your case what peaks my interest is your description of the runs fair cold (EGR is shutdown until converter temp comes up) then when the engine warms up (EGR system kicks in). Now the EGR system could just be aggravating poor mechanical compression. Which gets lengthy...
If the EGR has been ruled out then consider:
Find the bad cylinder, or get the expert to tell you which one it is. Then say "I'll run down to AutoZone and pick one up this weekend" (that's a joke by the way) and leave it at that.
a. Plug wire method. The engine may run better with the plug wire removed from the bad cylinder. Warning! do not drive a gasoline engine without spark plug fire for prolonged time due to contaminating the oil with raw fuel or if it runs a lot better you ma not care if the oil gets contaminated
b. Carefully examine each spark plug, and run compression test
Since you say that it stalls at idle you may have an intake valve that is not sealing during combustion. If it will do 80 is not a "bottom end" "swinging parts, crank, rods, pistons, melted pistons," problem. Melted pistons will cause loss of compression but the bottom end usually will not survive an 80 MPH run.
Lets get back to the intake valve and your cheap fix.
When an intake valve is stuck open the intake manifold vacuum is so low and contaminated the other cylinders cannot draw enough air/fuel charge at low RPM to run. Then the engine stalls.
How can an intake valve stick open or not properly seal?
Valve head worn, burnt or melted - requires removal of the head to repair Broken valve spring, valve springs return valves to the closed position - may be repairable without teardown Cracked Cylinder head - Teardown
What to do,
Leaky Intake Valve
- Pull the rocker arm cover
Try to determine if the valve is stuck
- Remove the rocker arm from the leaky valve
- Use the wooden handle end of a hammer and push on the valve stem with your hand on the head of the hammer, makes a good handle. It should be near impossible to move the valve without most of the energy you can muster up. A valve spring compression tool should do this quite easily but should bet met with skill and experience.
- OK so the valve moves a little with the hammer butt. Now compare to another valve. Don't be tempted to hit the valve stem with the hammer, If you knock out the retainers you will get a spring in your face.
- Time to remember this is on the cheap, no $100.00 bills, right?
- I have taken a cordless drill to a valve stem with lots of WD-40 sprayed down the stem and in the cylinder and rotated the valve very slowly, while spraying cleaner, to clean up a stem and seat. Can't get much of a cheaper try than that without a teardown.
Put the valve cover back on and only seal one side of the gasket. You will have to take it off again.
See if you have done any good, You may just want to run it without the cover in the driveway to shorten the test time. You should be able to tell pretty quick. While the cover is off check for slack in that rocker arm.
All else fails
- Pull the rocker arm cover again
- Remove the push rod and rocker from the leaky valve and leave them off
- Don't worry about the lifter, you or the cam couldn't eject it topside after 300,000+miles of crud anyway
- Up your oil viscosity to 20W50 below Interstate 70 (mid to southern states), 10W40 in northern winter climate. The higher viscosity will help push more oil topside buy increasing pressure to keep valves lubricated
Check for a worn timing chain. An extremely worn chain will cause all cyls compression to read a little low, not just one and the engine will run fairly close to the way you just described.
JAG, thanks for this great list of troubleshooting tips. Now, unfortunately, while I have tuned it up, changed the alternator, put in a radio, changed the oil, replaced the speedometer cable many times, the other stuff is a bit beyond me. My joints just aren't that flexible any more. Crawling inside or underneath this thing is a bit of a challenge these days. But, not totally out of the question. I just wish there were someone there to help and advise. Anyway, my truck is a '78 heavy duty emissions 350-4 barrel. No catalytic converter. Hence, no EGR valve??
Also, just found out that a bunch of oil has pushed its way up from the engine through the connecting hose into the carburetor/air filter housing, but not into the carb itself. The breather filter is soaked. Never done this before. I may have overfilled the crankcase recently. It was down past add (below dipstick level) and I added 3 quarts of Castrol
20/50. Yes, the engine does better on heavier oil. But, it is dying daily once it warms up. Idles down and that's it. So, hearing that it has no converter, any different thoughts? Or just proceed down the list? Wish I had a brother.
COLD ENGINE Start with removing the Vacuum line from the EGR valve and plug it off with your finger. Does the Idle smooth out? Do you feel vacuum against your finger. You should not feel a vacuum at an idle in the EGR vacuum line. Which means the EGR should not pass exhaust gas into the intake. If you do feel vacuum the motor idle may have smoothed out when you removed the line. Check the source of the vacuum. Gee wouldn't this be great if you found that you plumbed the EGR vacuum to a live manifold source. A cold motor with that many miles with a choke butterfly slammed shut would return enough un-burnt fuel back through the EGR to keep it running pretty good. Until the choke released of course. This would not be the first time a zero dollar fix cost
3 grand.
WARM ENGINE Remove the Vacuum line from the EGR valve and plug it off with your finger. Does the Idle smooth out? Do you feel vacuum against your finger. A road temp engine you should feel a small vacuum at an idle in the EGR vacuum line. Which means the EGR is passing some exhaust gas into the intake.
STUCK EGR Remove vacuum line from EGR and temporarily plug. Take vacuum from good source and apply to EGR valve. When vacuum is applied to an idle engine it should stall the engine. For your case you may need to use the fast idle choke cam or whatever to hold a slow as possible but steady RPM, then apply the live vacuum to the EGR valve. You should see a difference in RPM.
If the stuck EGR test has no tangible results then change the EGR valve and run the tests again.
The ERG valve is used to cool the Catalytic converter by replacing the intake atmospheric air with exhaust gas Which will richen mixture - less air during deceleration and hot idle and in turn very efficiently re-burns pollutants in the super heated converter. In your case what peaks my interest is your description of the runs fair cold (EGR is shutdown until converter temp comes up) then when the engine warms up (EGR system kicks in). Now the EGR system could just be aggravating poor mechanical compression. Which gets lengthy...
If the EGR has been ruled out then consider:
Find the bad cylinder, or get the expert to tell you which one it is. Then say "I'll run down to AutoZone and pick one up this weekend" (that's a joke by the way) and leave it at that.
a. Plug wire method. The engine may run better with the plug wire removed from the bad cylinder. Warning! do not drive a gasoline engine without spark plug fire for prolonged time due to contaminating the oil with raw fuel or if it runs a lot better you ma not care if the oil gets contaminated
b. Carefully examine each spark plug, and run compression test
Since you say that it stalls at idle you may have an intake valve that is not sealing during combustion. If it will do 80 is not a "bottom end" "swinging parts, crank, rods, pistons, melted pistons," problem. Melted pistons will cause loss of compression but the bottom end usually will not survive an 80 MPH run.
Lets get back to the intake valve and your cheap fix.
When an intake valve is stuck open the intake manifold vacuum is so low and contaminated the other cylinders cannot draw enough air/fuel charge at low RPM to run. Then the engine stalls.
How can an intake valve stick open or not properly seal?
Valve head worn, burnt or melted - requires removal of the head to repair Broken valve spring, valve springs return valves to the closed position - may be repairable without teardown Cracked Cylinder head - Teardown
What to do,
Leaky Intake Valve
- Pull the rocker arm cover
Try to determine if the valve is stuck
- Remove the rocker arm from the leaky valve
- Use the wooden handle end of a hammer and push on the valve stem with your hand on the head of the hammer, makes a good handle. It should be near impossible to move the valve without most of the energy you can muster up. A valve spring compression tool should do this quite easily but should bet met with skill and experience.
- OK so the valve moves a little with the hammer butt. Now compare to another valve. Don't be tempted to hit the valve stem with the hammer, If you knock out the retainers you will get a spring in your face.
- Time to remember this is on the cheap, no $100.00 bills, right?
- I have taken a cordless drill to a valve stem with lots of WD-40 sprayed down the stem and in the cylinder and rotated the valve very slowly, while spraying cleaner, to clean up a stem and seat. Can't get much of a cheaper try than that without a teardown.
Put the valve cover back on and only seal one side of the gasket. You will have to take it off again.
See if you have done any good, You may just want to run it without the cover in the driveway to shorten the test time. You should be able to tell pretty quick. While the cover is off check for slack in that rocker arm.
All else fails
- Pull the rocker arm cover again
- Remove the push rod and rocker from the leaky valve and leave them off
- Don't worry about the lifter, you or the cam couldn't eject it topside after 300,000+miles of crud anyway
- Up your oil viscosity to 20W50 below Interstate 70 (mid to southern states), 10W40 in northern winter climate. The higher viscosity will help push more oil topside buy increasing pressure to keep valves lubricated
Denny, I still think the timing is off. But, haven't had it checked out and I'm really not good at checking timing. My light is rather old and simplistic. But, I have trouble getting the distributor loose and tight again and finding the mark. The original chain lasted almost 300,000 miles. It was replaced a year or two ago. Of course, that doesn't mean the new one hasn't gone bad. I find it hard to locate someone who will troubleshoot the problem and tell me what it is and what it will cost. Everyone wants me to get rid of the truck or throw an engine into it. Easy to say, harder to do.
Try locating the vacuum line that goes to the bottom of the distributor. At an idle, this line should have full manifold vacuum. If it does not then plumb it into a port that does have idle vacuum. This will help.
Now the new symptom, oil in the air cleaner/filter. This is coming from the crankcase fresh air intake. The PCV (Positive Crankcase Ventilation) valve should cause or pull vacumm at the crankcase fresh air intake. If oil is blowing out of the crankcase fresh air intake then you have high crankcase pressure = combustion pressure that is leaking around work valves & rings = sings of pending doom. A plugged PCV valve could cause the oil in the breather (air cleaner/filter area) to be blown into the air filter.
Pull the PCV valve, with the vacumm line still attached, you should be able to feel the check ball snap inside the valve when you put your finger on the end at idle. With the engine off and the valve removed you should at least be able to shake it and hear the check ball inside rattle. If not try a new PCV.
I know your plight, I have seen hundreds of salvage cars & trucks that people poured a lot into to keep them up just to loose the motor. I just sent one away this summer that lost the mains and hammered out a rod. There were a lot of good parts on that one, no time or money to long or short block it.
That's the biggest problem with Usenet, people posting about things they clearly don't understand and trying to pass them off as facts. If you were to put a vacuum gauge on both ported and manifold sources and monitor them both you'd see that idle is the only time there are any real differences with the ported vac being at zero. Bob
This is exactly the reason I hate buying old cars from people who "think" they know how to work on stuff.
People who dick stuff up just to make somthing "run" should not be allowed to touch vehicles. I can't count the number of times I've opened the hood of a recently acquired project vehicle and seen the clasic symptoms of a previous owner with a "duct tape and baling-wire mentality." Golf tees or screws stuck in vaccum lines, wires spliced and running everywhere, etc, etc, etc...
Ann needs to fix the motor, not band-aid it. You can't ride a lame horse very long or very fast...
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