My 1999 5.2L has a problem with the RPMs surging under acceleration in 2nd gear near or at wide-open-throttle. This usually happens when merging onto the freeway or passing a vehicle; the transmission kicks down into 2nd gear and as the truck accelerates, the engine RPMs surge/oscillate as the RPMs climb. Occasionally, stepping off the throttle and flooring the throttle again will cause the engine to then accelerate smoothly; and, I don't experience the problem when accelerating from a stop, only when the transmission kicks down into 2nd from 3rd or 4th gear. I don't experience the problem when accelerating in 3rd gear.

Transmission filter, governor pressure switch and solenoid were replaced last year; could this be a band adjustment issue?

 

Get the service manual from the FAQ/DIY section and a cheap analog multimeter and test the TPS.

 

TPS shows .75v at closed throttle and 3.65v at wide open throttle. Voltage change across the sweep of throttle appears linear and shows no intermittent interruptions in the signal.

Could the fuel synch cause this? I've never touched the index of the distributor, but that doesn't mean somebody else didn't.

The engine otherwise drives fine, gets normal fuel economy, and accelerates smoothly in all gears, except in 2nd at WOT after the transmission has kicked down from 3rd or 4th.

 

Nevermind...the distributor/cam signal would only be used for phasing the correct 360-degree portion of the 720-degree cycle; it never would be used to phase any given injection event with respect to the valve-opening event (the injection events are still timed with respect to the crank-position signal, unless the engineers were truly a bunch of idiots). If the fuel-synch were out of phase, it should have drivability problems throughout the RPM range.

I'll chase some other lead...

 

Cam sensor clues the PCM in to just where the engine is in the firing order. It has a pretty small tolerance for error.... only about +- 7 degrees..... But, I agree, I don't think that is your problem.

Not dropping a cylinder on hard acceleration is it? (dirty injector?)

 

I don't think it is. The surging is relatively smooth and cyclical throughout the acceleration; if it were dropping a cylinder, I might expect the power to be down throughout the acceleration, not picking up and dropping off at ~1hz (give or take).

I haven't thrown any codes, so whatever the issue, it is not triggering either a misfire or lean code.

 

I think it's just the by way of how the intake manifold (keg) has run out of air for those RPMS in 2nd. It's choking to get more and the flow just isn't helping. I'm saying this in light of reading the other posts and your updates.

 

So...then everybody has this problem?

When 99.9% of all driving across all RPMs for all engines is choked by a partially open throttle-plate, any surging related to air flow is the direct result of improper fueling or ignition.

 

Well, you checked your TPS, crank, and cam sensor with some degree of confidence judging by your detailed post.

I guess I'll ask....what is the specs/condition of your plugs, cap, rotor, wires, and coil? Injectors (as HeyYou mentioned)?

Only thing I might mention from your OP regarding tranny, but your symptoms (as described) don't seem to indicate it to me, is the tranny speed sensor having a contribution.

I'm reading that you only experience this surge in 2nd at what rpms again? I presumed > 2500...


Any mods on this engine?

 

I checked the TPS. I'm assuming the crank and cam (distributor) sensors are fine as drivability is otherwise fine and there are no error codes/CEL. I would need an oscilloscope to *actually* check these two sensors, but I do not suspect them.

Cap, rotor, wires and coil were replaced a few months ago. Plugs look fine, not fouled.

I don't have a fixture or driver to inspect the fuel injectors, so aside from replacing them as a precaution, I'm relying on either a misfire or rich/lean error code to indicate they may be a problem.

Would there be other shifting issues associated with a bad TSS? Since replacing the governor pressure sensor and solenoid, the transmission shifts as expected, does not hang up in any gears, kicks down normally, and the converter locks/unlocks normally. Thinking about the surging more, I would lean more towards it being an engine issue than a transmission/slipping issue; when the rpms surge, the truck surges (if there was slippage, rpm would surge but that power wouldn't make it to the driveline...?).

I have not made note of the min RPM; since this typically happens when kicking down into 2nd from 3rd or 4th, I would agree the RPMs are generally above 2500. The only time I'm at WOT in 3rd at these RPMs are when towing...which I'll be doing again next weekend, so I may have an update if the surging persists.

I don't know the history of this engine; my assumption is no. Other [ir]relevant info: I've also replaced the timing set, IAC, and fuel pump within the last year.