C60X running not as well as it should....

[warren brown]

Hi everyone - had to move the C60X to our new house (about 40km) and for the first time since I've had it the truck was struggling up hills - or under load. At idle it sounds fine but it develops a chug - as though it's running on five cylinders and runs out of puff. Normally it lopes along pretty well - it starts and idles very well but once you give it a few herbs it doesn't sound quite as smooth. I'm going to remove the plugs and leads and probably replace them - and have a squizz at the distributor cap in case there's a crack - I hope it's not something catastrophic but I'll start with the simple things first. Are there other things I should check I haven't thought about? Does anybody know what size spark plugs they are for the GM c60X engine and any tips on plug removal before I start dismantling the cab? Cheers and many thanks - Warren

[hrpearce]

It sounds like a dirty carbie problem, restricted air intake or worn accelerator pump.

[Howard]

When you say 'chug', do you mean like a missfire? Or more of a surge?
Do you feel this chug? or hear it? or both? Will it rev OK standing in neutral or does it only play up when moving along? All gears?
CHeers
H
PS Where is the new home?

[warren brown]

Hi Howard! - couldn't hear the 'chug' from inside the cab - it wasn't apparent at idle at all - a couple of mates said it sounded chaff-cutterish from outside ... I'll post an iphone video they took ...

[motto]

G'day Warren
The GMC is a good engine and I doubt there is much wrong with it.
You're problem may be simply that the fuel has gone off from standing, it can have quite a short shelf life these days.
If the fuel is fresh then you're next suspect is the ignition system and that means plugs, leads, points, condenser and coil.

David

[Phil Waterman]

Hi Warren

Start with a list of possible causes once you have a list of possible put the list in order of difficulty to check and fix. Once you have done that start with simple end of the list.

Now for my basic list for loss of power:

1. Bad gas or water in the fuel
2. Plugged or nearly plugged fuel filter, this fits your runs but doesn't take a load
3. One at a time unplug and replug each spark lead from plug and distributor (if you have had any of the leads off just before this problem started check the firing order)
4. Loose or broken spark lead, quick check for this is to ground a screw drive with a jumper lead, then with engine running ground out each spark plug one at a time see if find a plug that when you ground it out doesn't make a difference. If you find a plug check or replace the lead you can check it by unhook in it from the plug and holding it 1/8 - 1/4 from block if you get a good spark pull the plug.
5. If the plug looks good swap it with a another and see if the problem moves.

Now to start checking for internal

6. Connect a vacuum gauge and look for a quick fluctuation, which would be an indication of a problem.

7. Do a compression test look for low readings - if you find one low cylinder do not assume it is time for rebuild another test.

8. Check the valve clearance, you are looking for exhaust valves in particular that have no clearance. If you find that you have less than what the manual calls for you may get lucky and adjusting the valves may restore the power. The problem is that with no clearance the valve doesn't seal. This assumes that your engine doesn't have hydraulic lifters.

All of the problems I've described have happened to one of my trucks.

Cheers Phil

[Tony Wheeler]

Originally Posted by warren brown

it starts and idles very well but once you give it a few herbs it doesn't sound quite as smooth.

Sounds like fuel starvation to me Warren, although spark breakdown can produce similar symptoms. Best way to diagnose is to play with the choke while driving. If it responds to choke under load you know it's a fuel problem rather than spark. In this case I suspect you may have sucked up some water into the small inline fuel filter. They stop water getting to the carby but the wet paper element restricts fuel flow. It's certainly the first thing to replace as you say, and you may also need to drain the tank to prevent recurrence. Often there's quite a bit of water swilling around the bottom, which accumulates through condensation over time, esp. if the tank is near empty. Alternatively you can run it without a fuel filter, which allows any water to pass harmlessly through the carby. Fuel filters are quite unnecessary in my experience, provided of course the fuel tanks are free of rust flakes and wasps nests!

I agree with Phil re valve clearance adjustment, which is generally routine with a major tune up like this. Anyway good luck with it all and I'm sure there's no major problem.

[Phil Waterman]

Hi All

Here are some photos of the inline filter on my Pat 12 C60L that started burping and farting recently when under full throttle on long up grades.
W Fuel Filter 2014 - 001.jpg
W Fuel Filter 2014 - 002.jpg
First two photos are with the regular fuel pump sucking fuel the last is with the electric fuel pump at the tank running note what happened to the length of the filter element.
W Fuel Filter 2014 - 006.jpg

Yes replacing the filter did solve the problem.

Cheers Phil

[warren brown]

Phil thanks so much for the tip - I'm heading in to pick up new fuel filters as we speak. When I get back I'll do an autopsy on the old filter and post a photo. I think my filter was personally installed by King George VI when the truck was built. Next step - air cleaner...and then onto the ignition system... wish me luck...