RPM bounce. Engine surge or Trans?

wondering in anybody has ever experienced this or could tell me what to look for.

Truck is a 2004 3.4l Automatic with TRD S/C and 7th. It has 110,000 miles.

Truck was at operating temperature and I was accelerating up a slight incline at ~30mph when my tachometer bounced between 1800 and 2200rpm about 4 Times. I let off the gas and it stopped. I could hear it but I’m not really not sure if I could feel any surge. I tired to recreate it but I was unable to. I believe this happened twice but I was caught off guard the first time so didn’t know what to think of it.

Considering there wasn’t a high jump in RPMs I don’t think it’s a trans issue. Howerver, I did check the transmission fluid. It’s dark red so it seems to still have some life left. And I was already planning on drain and refill multiple times over the next few weeks. The truck has no history of trans service.

 

Good to check the basic things first like tranny fluid, usually the simplest answer is the correct one. What about fuel filter? I think I remember you telling me that you didn't have many records of maintenance on this truck. Might be worth changing the fuel filter out to make sure you're not having a fueling issue. Using 91 octane gas right? And you installed the Walbro fuel pump with the 7th kit? I'd run some injector cleaner through it as well after you swap the filter out.

 

Did the fuel filter a few weeks ago. Did the pump as well.

I need to add that I might be having some issues with the pump.

On cold starts it takes a lot longer to crank. Sometimes I have to crank it twice to get it running. I emailed Gadget about it. He said it’s normal for the pump to loose pressure after it’s been sitting but if I want to send it in they’ll have to send it off for a few weeks to test it to determine if it’s bad. What a waste of time. Might as well buy a new one.


EDIT: been running 93 octane even before S/C

EDIT 2: Got the MotorVac carbon clean service done before S/C and ran a bottle of the Techron before fuel filter.

 

Tranny fluid looks fine. No burnt smell. Here’s some on a paper towel.

 

Yeah trans fluid look ok, if you're going to do a drain and fill soon anyway I wouldn't worry about it, as long as the level is correct.

That's odd about the pump, I have never had it take longer to crank, even in sub-freezing temperatures. It's possible that the problems are related.

If I were going to replace my fuel pump again, I would probably go with a higher flow AEM, like this one:
https://www.summitracing.com/parts/avm-50-1200?seid=srese1

 

Very possible it’s the pump. Don’t know why that would cause the RPM bounce. I guess it could also be the 7th injector that’s leaking.

I guess I’ll run it and cut it off and remove the 7th to see if it leaks. If it’s clean it’s probably the pump. Or another injector. Which would be very bad timing because I had no problems before the S/C.

 

Update. Reading other forums and posts I don’t think it’s in injector or the pump. I’ve seen other posts with people that have the S/C and the 7th with the same long start issues. Changing the pump to a new walbro didn’t change things. I also need to add that it starts right up on cold starts with a full tank. So it’s possible that something else is going on with the tank.

Now back to the Tach bounce. Are there any sensors or valves anywhere that could cause this?

I probably need to add that this happened after a 30 minute drive on the interstate which included accelerating to overtake slower drivers. Got to town and parked for 20 minutes. Then, after starting and driving in town again it happened twice. Hasn’t happened since.

I guess it’s possible my trans was overheated but it was also fairly cool outside. ~60 degrees. No trans cooler on Auto with S/C