I just had a really scary ride home on the highway.
Before I start, my truck has a manual transmission.
I got onto the highway and began accellerating upto speed - 100km/h
Through first upto 40, shifted to second and got to about 70km/h when the truck began to kangaroo backwards and forwards like it was about to stall so I shifted to third hoping it would stop but it continued to kangaroo whilst I dropped speed so much that I was back into second and then into first again, still kangarooing. Luckily I live at the top of the hill about 2kms from where I entered the highway so I limped up the hill in first, all the time kangarooing, constantly feeling like it was about to cut out.

I'm not very mechanically minded so I don't know if this sounds like it might be miss firing or something worse. Hopefully this sounds familiar to someone and I can get some help.

Many thanks in advance as I'm pretty worried about driving it again at the moment.

Jamie

 

When you push in the clutch, does everything smooth out?

 

I can't remember :/ I *think* it does smooth out with the clutch pressed down.
What are you thinking?
By the way, around town, its perfect, the speed limit is 50km/h and i can shift to third and cruise at 50 all day without a worry.
It seems to happen if i need to go past a certain travel point with the accellerator pedal...
You think its the plugs? Maybe the distributor cap? Or possibly running too lean?
Or any of the above? Possibly something worse..?

EDIT: I forgot to mention, when this happened last night, I could hear the engine cutting and then firing again - this was the cause of the kangarooing. Sorry I wasn't clear about that the first time..

 

There is a tendency for lifted trucks with larger tires to have a problem with what is affectionately called the "Death Wobble". This happens at various speeds depending on the condition of the steering components and causes the front end to jump all over the place. At first your description sounded sort of like this.

My next thought was that your clutch is slipping, grabbing, slipping, grabbing, etc as that could be dependent on requested power (rate of acceleration). But again, that does not sound right to your latest description.

It sounds as though you have a fuel delivery problem. The first thing that I would suggest is that you toss a new fuel filter at it and see how it affects the problem. With a carburetor, there is a fixed amount of fuel in the fuel bowl. That amount is regulated by the float which controls the flow of fuel from the fuel pump. Your problem could be a clogged fuel filter, a bad float, or a weak fuel pump. The easiest and cheapest thing to do off the bat is to change the fuel filter. You may want to go through and rebuild the carburetor if you have the time.

 

Thanks Kyle.
I'll certainly try changing the fuel filter, that sounds like a good plan.
I just swapped out all the spark plugs, they were a little tanned with a rust type of compound on the electrodes but the gaps were good for all but one which was at 0.035 instead of 0.045.
I drove it back down the highway, no problems. Turned around and starting coming back up the hill when it happened again in second, around 80 km/h this time but not as bad as last night - although, I was a lot more careful with the accellerator pedal so it might have just been my input making things more gentle. It seems to be at the hill, where I have to give the accellerator pedal a little more push, that the kangarooing happens...

About rebuilding the carb... hows that going to be for a complete novice? :/ aha.

 

The difficulty comes down to what type of carb is on the motor. It does not look like the 6.6L (400cid) was offered in '81 so if the motor is not original, I doubt the carb is... It is possible that someone reused the carb from the original motor and if the original motor was a 5.7L (350cid) v8, then the carb would be a Rochester QuadraJet M4MC.

If you can, snap a picture of the carb and write down any numbers off of it for identification purposes and I will try to walk you through the rebuild process. I have a Rochester M4MC sitting on the bench now that I could throw back together to show you the proper orientation of the linkages, etc as well as walk you through the disassembly process and things to check/repair along the way.

 

The engine swap is where the truck becomes a huge headache for me. You're right that the 6.6 wasn't offered in '81 but I've got no receipts or anything to tell me what age the engine is or where it came from. The Haynes manual says that all V8 engines covered by the book have a tab with a serial number on it for the engine but I can't even find that tab...
Take this for example, I took one of the old spark plugs to Canadian Tire today to replace them and the guy searched my vehicle on there computer - of course no 6.6 for an '81 model so I said to try the '79 model as I know that was offered with that engine. Turns out that the plug I took out of my engine doesn't match what GM suggests for that 6.6 *sigh* we tried 3 years back from '79 and still no match.
I picked up the same plugs that came out of my engine in the end as I knew they atleast had it running and they didn't look too bad on the electrodes.
I wanted to pick up some distributor cables to replace as well but with out knowing where my 6.6 came from and how old it is, theres about 4 different cable kits that might work. It's a bit of a nightmare :/

On a lighter note, that would be awesome if you could point me in the right direction through rebuilding the carb. As I've mentioned, I've got the Haynes manual for the truck so that might help me a little too.
I'll hopefully get around to replacing the fuel filter tomorrow and while I'm at it I'll get a pic of the Carb and note product codes and I'll get back to you.
What would I need to purchase new for the carb rebuild? Another float perhaps or any gaskets, etc?

EDIT: So I changed the fuel filter today Kyle. I got some pics for you aswell - I'll upload them tomorrow. I came across a pipe that I think should be plugged into the carb at the back into a cylindrical piece attached to the carb (the side facing the distributor) but the pipe has a screw clogging the end so it's not come loose - its been unplugged for some reason...

The carb is a Rochester QuadraJet and the product code is 17081220 and under that it says 3040 DDR. I also came across a pipe leaving the fuel vapour canister that is cut about 18" from the canister and can't see where it plugs in, if anywhere..?

Anyway, after changing the fuel filter, I drove out onto the highway, going down the hill in second. I got to about a third of the accelerator travel when the engine stuttering happened again, not right away but when the revs increased. I drove around town using no more than an inch of accellerator travel without a problem but coming back up the hill on the highway it was worse than the first time and halfway up I had to hold down the clutch to stop from stalling. I stopped to the side of the highway and struggled to rev the engine up, it kept almost stalling instead. Finally I got the revs up, tried to launch and got about a meter more up the hill, easing out the clutch before it stalled again and then wouldn't start - I had to get my neighbour to tow me into our yard :/ haha.

I think this might be linked to the engine starting trouble I was experiencing.. Anyway I should note, before the cutting out, after I fitted the new fuel filter it took a while to start but I put that down to the fuel having to run through the new filter. Anyway she fired up and I left her idling for a good ten minutes - no problem. I sat and revved her to around the top off the RPMs (no tach by the way) - no problems. It only seems to happen when its in gear and reaching a certain amount of RPM. Is this whats referred to as "under load"?

So anyhow, what do you think? Should I go ahead and replace the fuel pump?

Many thanks in advance.
Jamie

 

Heres some pics, the first is of the cylinderical part attached to the back of the carb which has an inlet that for some reason is diconnected on my truck..
Any thoughts?



The second pic is of a pipe I found led on the rocker cover with a screw clogging the end. I'm guessing this is the pipe that should be connected to the previously mentioned inlet..?



The third and final pic is of some aftermarket part but I don't know what it is. You can see two cables hanging down that are unplugged and have been since I've owned it. What is it though?

 

Take a picture of the carb from various angles showing the whole carb. I will be able to identify it based on your pictures.

The vacuum line for the rear vacuum break assembly (which is what I think that is) is the one off to the side. The carb is likely an M4MC or M4ME (CLICK HERE).

 

Hey Kyle. Theres an edit in my previous post about the carb - its a rochester quadrajet 17081220 3040 DDR and I changed the fuel filter yesterday but still no good. Read up for what happened after I fitted it :/ haha.
Should I go about replacing the fuel pump do you think?

Also what do you think about that unused inlet in the rear of my carb? Is it normal to have nothing plugged into it? :/