rough running, about to sputter out

The truck calls for vented caps.

There are no vents plumbed into my fuel tanks.

The caps have a ball and spring check valve in them, in addition to the float with the flap on top that will seal the tank if it moves upward in its cradle.

 

I went outside and checked again.

There are no vents on my entire fuel system anywhere, other than the vented caps.

The vented caps are strange critters. They have a little plastic cylinder that rides in a vertical cradle. On the top of the cylinder is a little flap. When the cylinder reaches the top of its travel, which is only a few millimeters, it seals off the vent hole. If pressure builds in the tanks, it can only reach a certain point when the ball and spring come into play, releasing any excess pressure.

In my old caps, the little steel ball was corroded into the aluminum cap, solid, no movement, no pressure relief.

Perhaps my tanks were slowly building pressure, and when it reached a certain point, the engine acted like fuel starvation. I read somewhere that if fuel pressure gets too high, the ECM will not fire the injectors.

I wish I would have had a gauge.

Well, I do now, a TLK-133.

 

I think the problem is fixed. Once I drilled the holes, I ran the truck 650 miles back home without any problem.

With the new caps, I don't think there will be any more vent problems.

I still have a problem of low power, however.

I thought I had low power because I had no turbo boost, but I think it's the other way around. I have no turbo boost because I have low power.

The engine runs. It does the job, but in a very anemic manner. It's not smoking. It's just weak, as if the ECM were downrated. It was running fine when the rear axle went out on me. I parked it for 5 years. When I put it back on the road, I noticed right away that I had no turbo boost. At least the gauge was showing no boost. I figured maybe the gauge seized up over 5 years. But if the engine is getting the right amount of fuel, according to pedal position, and there is no turbo boost, it should smoke. I know because I got busted for emissions when I had a crack in the CAC some years back.

No, the exhaust is clean. There is no boost because the engine is not producing enough exhaust to spool up the turbo.

There's one for ya!

What's the answer to that one? Remember! It was fine when I parked it. Something changed while it was sitting for 5 years. Also, the jakes don't work and the cruise doesn't work. They were working when the truck was parked.

 

All of the problems I had with the truck running rough and wanting to shut down were due to the fuel tank caps. I put new caps on both tanks and have been running a lot of miles with no problems. The only change I made was replacing the caps. I plugged the hole that I had drilled in the tank.

There is a check valve in the cap. On the old caps, the check valves were seized, steel ball stuck tight in the aluminum cap.

At the time, I had no fuel pressure gauge. Without a gauge, I was assuming I had a case of fuel starvation, but now I think it may have been a case of fuel pressure running too high. I'll never know for sure.

I have since installed a fuel pressure gauge. Man, it's a good thing to have. My truck came with the minimum gauge package which didn't include fuel pressure. Every big truck should have a fuel pressure gauge.

I cannibalized the turbo boost gauge from my other truck. I wasn't showing boost pressure because the gauge quit working after sitting for 5 years. Boost is good. Engine is running properly.

I believe the reason the fuel problem was intermittent was that I wasn't uniform in my tightening of the caps. Sometimes I spun them on without tightening them. Looking back, in retrospect, I realize that when I did that, leaving the caps loose, the problem did not manifest itself, but then for some reason, the next time, I'd tighten the cap, and within 60 or 70 miles, the engine would act up, behaving as if it was starved for fuel.

Whenever I took off the caps to pour in additives, I was relieving pressure, temporarily solving the problem. Usually, I put in the additives at the same time I changed filters, so I was assuming that it was filter replacement that was temporarily relieving the problem. In actuality, it was the simple act of removing the caps that got the truck running again.

All this looks clear now in retrospect. All that trouble I went through could have been avoided just by leaving the caps loose until I could buy new ones.

Also, I found out that this engine, a 1993 model, does not come with a check valve at the back of the cylinder head, only an orifice fitting. I don't understand this, but I do know that at more than one dealership I listened to the parts man tell me that according to his search, my engine, according to my serial number, does not call for this check valve. It isn't there in the book, and it isn't, and never was, on my engine. I did experience a loss of prime problem with this truck, with a bad problem of the engine failing to fire up, sometimes running the batteries dead. I solved this by installing my own check valves, first placing one at the rear of the cylinder head, and then by placing one at the output of the fuel transfer pump, directly before the secondary fuel filter. I removed the check valve that I placed at the back of the cylinder head. The check valve at the output of the pump suffices to prevent loss of prime. The engine always starts immediately upon pushing the button and has ever since I installed that check valve.