Rumps at start up
 

1996 F350 with 7.3 diesel. 142,000 miles.

All of a sudden got a case of rumps at start up. depressing accelerator a few times makes it go away. This is an intermittent problem. Changed fuel filter first, even though it was fairly new. No change.

Took to a highly recommended local diesel shop.No codes show on code reader and no Chech engine light. They diagnosed Injector Control Pressure Sensor with out of range voltages. Changed it. Problem came back after a few miles of driving.

Found wire harness in valley was in bad shape, ordered new Ford harness ($100) installed it. No change. Did not charge me since the ICP sensor did not fix problem.

They put in a new $200. sensor that has to do with the oil pressure going to injectors. This made no change. Took it back out and put mine back in. Just for kicks changed Cam Sensor, even though it was only 4 years old. No change.

Guy has so many hours in it he gave up.

Valve cover wiring harnesses look good. Covers not pulled.

Any ideas?

Mike B.

What is your fuel pressure?

Low fuel pressure can make it do that.

Do you have a scanner? With out one things can be tough to figure out.

Truck an automatic?

I have the same question as tshrager, is it an automatic? And this rump, is it kind of like a gasser with a big cam until it evens out? Try starting it in 'N'. If it starts smooth in 'N', it's probably a Transmission Range Sensor on the transmission. It's a pretty simple and not too costly fix.

had the same issue.. except mine did it almost after every start. no codes. even starting in neutral did not make a difference.
It ended up to be the transmission range sensor was faulty. replaced it and never had an issue again.. but then of course i installed a 5-speed :-)

You guys hit it on the nose. I put in Neutral, started smoooth as silk. Put in Park, Rumps came back. Put in Neutral again, Smoooth. Put in Park again, Rumps came back.

Went to Autozone, $34.95 later, Rumps are gone.

Thank you VERY MUCH.

Glad we could help. Thank you for returning and answering. Just a heads up, if it starts to act up again spend the coin on a motorcraft part. I've had bad sensors out of the box from napa and the likes.

Mine does it also. Tried numerous things, and finally discovered starts like a champ with the chip unplugged. Oh well, I feed it some go pedal on start up, I like my chip...haha.

^^^^ Why not contact whoever made or programmed the chip, and get it re-programmed / re-burned the way it should be?

I don't know who programmed it. The PO didn't even know it was chipped, I found the selector knob under the dash. I thought about sending it in, but honestly, I'm just too cheap/broke.

Ipr
 

It took me over a year to figure it out and never actually thought it was a failing part. Turns out it's the injection pressure regulator.