By Scott A. Keen (Scottkeen) on Sunday, September 30, 2001 - 04:32 pm: Edit

Just came back from a 300-mile trip in my 1997 SD7.

On the way down, and the way back, I had an incident of "surging" and "bogging" on each leg of the trip.

The symptoms are:
- Constant surging and bogging for about 1 minute.
- Mashing the accelerator had no effect on increasing the speed, and seemed to bog down the car.

I've been running 93 octange. This problem occurred once when the tank was 25% full, and once when the tank was 100% full.

The first time it happened, I pulled over, filled up the tank, and went on my way.

The second time, I had just filled the tank a few miles back, and when it happened I just kept a light touch on the accelerator and eventually the surging and bogging stopped.

Also, all along the trip, there was *predicatble* mini-surging and mini-bogging at 70mph, but not above or below the speed.

Also, at one point the cruise control kicked out all by itself.

I can't figure it out. I ran my OBD scan when I got home, and I have 0 reported errors. I also ran the scanner enroute (I had my laptop and OBD cables handy), and the results showed 0 error codes, and the 02 sensors reported good.

Any ideas?

By Robert Mann (Oldscout) on Sunday, September 30, 2001 - 05:04 pm: Edit

Sound like a fuel pressure problem. How many miles on the filter?

By Axel Haakonsen (Axel) on Sunday, September 30, 2001 - 05:08 pm: Edit

I had a similar symptoms driving back from Las Vegas a year ago. Changed the fuel filter, and the problem went away. Some people have also reported the same symptoms being caused by a bad speed sensor.

By Steve (Steve2) on Sunday, September 30, 2001 - 05:40 pm: Edit

i'm with axel - check for fault codes 1st - if clean - then change filter

steve

By Scott A. Keen (Scottkeen) on Sunday, September 30, 2001 - 05:57 pm: Edit

Fault codes are OK. I'm gonna change the fuel filter. Where is it? Is there more than one? Somewhere here I read that I can replace the fuel filter with a GM (?) part. If so, anyone know the part # match?

Thanks for the replies

By I-Man on Sunday, September 30, 2001 - 07:46 pm: Edit

I had this problem driving from SLC, UT to Irvine, CA last week. I took my disco into a rover shop and explained the issue. I was told it could be many things but in the end it turned out to be a speed sensor on the transmission!!! Since the repair three days ago, I have logged +1,000 miles over the weekend with no problems. I do plan to replace the fuel filter next week. FYI, my disco is a late model '97 with 80,000 miles. I hope this helps...

By Alex Schubow (Alex) on Sunday, September 30, 2001 - 07:53 pm: Edit

Speed sensor. Change it out, Crabtree has them for $60.

Alex

By Scott A. Keen (Scottkeen) on Monday, October 01, 2001 - 03:19 am: Edit

OK, I'll change the speed sensor.

Is it an easy change? Where is it located?

Thanks

By Alex Schubow (Alex) on Monday, October 01, 2001 - 05:01 am: Edit

Its on the backside of the transfercase, b/w the transfercase and the brake drum. PITA to get to without a long 5mm ball-end socket. One screw mounting.

Alex

By chrisvonc on Monday, October 01, 2001 - 01:13 pm: Edit

Also, check the MAS. Mine had dirt and mud in there which produced problems like the ones you described.

Chris

By Scott A. Keen (Scottkeen) on Monday, October 01, 2001 - 04:21 pm: Edit

Sorry for the ignorance -- what's the "MAS" ?

By Robert Mann (Oldscout) on Monday, October 01, 2001 - 04:34 pm: Edit

MAS = mas air sensor, the more common name is MAF mass air flow sensor. It sits in-between the throttle body and the air cleaner.