Intermittent surging?

[Dave7.3]

Recently I've been encountering an odd surging with my truck. It has happened 3 times now and is leaving me puzzled...

The first time it happened, I was cruising at 60mph holding 2100 rpms at around 480*F EGTs. I slowed down a moment to let a car off the on-ramp and when I stabbed the throttle to get back to speed, my rpms snapped to ~3000 rpms instantly...but my speed stayed the same. I backed out of the throttle and checked my gauges, nothing out of the ordinary. Rolled into the throttle again and as soon as I passed 2200, it snapped to 3000 rpms again.
I pulled over and checked things out, everything was running fine and nothing out of the ordinary... Got back in and drove home without anymore issue.

The first thing I thought of was maybe a bit of clutch slip...but I can slam through the gears hard with a load without missing a beat, so I doubt it could be that.
Maybe a fueling issue? Would have guessed the tanks were low and my gauge could be off, but both were filled to the brim earlier this week. However my IP does seem to be weeping a little...wondering if that could be a sign... Although it didn't smoke a puff during the surging ordeal like I thought it might.

Just a very weird issue I've never encountered before. Any ideas? Almost leaning toward the weeping pump but I'm no expert... Thanks in advance.

-Dave

 

[George D.]

The fitting in the top of the IP has a check valve in it could be plugged causing the body pressure in the IP to go hangwire when you get on it. you could also be sucking air some where.

 

[Dave7.3]

The fitting in the top of the IP has a check valve in it could be plugged causing the body pressure in the IP to go hangwire when you get on it. you could also be sucking air some where.

That is a good idea, thanks. I will have to take a look at that in the morning. I wish this surging wasn't so intermittent...it would be a heck of alot easier to diagnose if it were consistent!

 

[OLDBULL8]

Recently I've been encountering an odd surging with my truck. It has happened 3 times now and is leaving me puzzled...

The first time it happened, I was cruising at 60mph holding 2100 rpms at around 480*F EGTs. I slowed down a moment to let a car off the on-ramp and when I stabbed the throttle to get back to speed, my rpms snapped to ~3000 rpms instantly...but my speed stayed the same. I backed out of the throttle and checked my gauges, nothing out of the ordinary. Rolled into the throttle again and as soon as I passed 2200, it snapped to 3000 rpms again.
I pulled over and checked things out, everything was running fine and nothing out of the ordinary... Got back in and drove home without anymore issue.

The first thing I thought of was maybe a bit of clutch slip...but I can slam through the gears hard with a load without missing a beat, so I doubt it could be that.
Maybe a fueling issue? Would have guessed the tanks were low and my gauge could be off, but both were filled to the brim earlier this week. However my IP does seem to be weeping a little...wondering if that could be a sign... Although it didn't smoke a puff during the surging ordeal like I thought it might.

Just a very weird issue I've never encountered before. Any ideas? Almost leaning toward the weeping pump but I'm no expert... Thanks in advance.

-Dave

Your engine speeds up (confirmed by the tach) but your speed didn't change (confirmed by your speedometer), that happening like that could only be the clutch slipping, the IP could not be at fault if the engine speeds up. Surging to me, would be the truck speed would go up and down like you would be loosing power from lack of fuel and then regaining fuel to speed up again. I see you have a turbo, when you punched it, your feeding more fuel, which would make the turbo spin higher giving the engine more power instantly, which in turn could make the clutch slip, hence higher RPM, no change in speed.

 

[Dave7.3]

Your engine speeds up (confirmed by the tach) but your speed didn't change (confirmed by your speedometer), that happening like that could only be the clutch slipping, the IP could not be at fault if the engine speeds up. Surging to me, would be the truck speed would go up and down like you would be loosing power from lack of fuel and then regaining fuel to speed up again. I see you have a turbo, when you punched it, your feeding more fuel, which would make the turbo spin higher giving the engine more power instantly, which in turn could make the clutch slip, hence higher RPM, no change in speed.

Right on, that is what first lead me to think it could be a bit of a slip. Especially since this only has occurred in Overdrive. At the same time, the other 99% of the time I don't have it act up at all. In fact, it never happens when I'm towing my horse trailer either...

 

[OLDBULL8]

Probably won't happen while towing, engine already has a good load on it and can't speed up rapidly when punched. All do to HP unless your in the torque range 1600 - 2000 RPM.

 

[Dave7.3]

Probably won't happen while towing, engine already has a good load on it and can't speed up rapidly when punched. All do to HP unless your in the torque range 1600 - 2000 RPM.

If anything I figured it would be worse in that situation, but I see what you mean. I guess that means I get to shop for clutches in the future...

 

[George D.]

MY bad miss the part of the speed not changing.

 

[FordCoalRoller]

can you tell that the actual engine rpms increase to 3k via sound/feel or are you soully relying on the tach?

 

[Dave7.3]

can you tell that the actual engine rpms increase to 3k via sound/feel or are you soully relying on the tach?

I can definitely hear the engine pick up in rpm. In fact, when it jumps to 3k it sounds and feels like pushing in the clutch basically.