I have a 97' Disco and I have had a bunch of work done on it, Head gasket replaced, steering box, water pump, plugs, wires, cats...... But one thing this rover has started to do lately is hesitate on the highway at a a constant speed. Any ideas as to what may be the cause? I have sunk over $4000 in it and need some advice. Many Thanks

 

Check fuel pressure at schrader (tire ) valve on right side fuel rail. 32-34 PSI when running. If no misfire codes, consider cleaning MAF. Now that part is like $1400, so use a spray made for MAFs, and do it when truck is cold, and you have not turned on ignition. Even just to listen to the radio. Powering up the sensor heats a spot inside to 350F above ambient, and cold spray on hot parts is stressful.

 

How would you describe the hesitation? Is the engine reverting to idle speed for a period and then recovering?

 

hmm... could also be VSS is beginning to fail. Vehicle Speed Sensor is monitored by ECU to prevent truck from being driven at high speed, and when sensor fails the ECU starts shutting down cylinders. So truck will protect you if you try to drive all the way around I-285 in 20 minutes.... Usually is intermit to begin with, and shows up at high way cruise speed.

 

not meaning to high jack this post but this sounds like exactly what my 97 disco is doing, i posted in this section about my 97 doing the same exact thing.

 

The hesitation is randomly constant, meaning randomly when I drive up and down the interstate, but the hesitation is a constant putt,putt,putt,putt and the RPM's drop. but it comes back up. It feels like I lose a cylinder along the way but with it being in 2 different shops lately and a ton of work done, they should of caught that perhaps???

 

OH, the "Check Engine" light does NOT come on when this happens

 

Sounds like VSS. You'll know if the speedometer wigs out when it happens (doubt it though) or with a live data scanner like an ultragauge (should be obvious).

 

You can unplug the VSS and drive (use your GPS for speed) to test. As far as catch, many diagnostic skills have been dulled by depending on the code scanner too much.

The CEL not coming on means that no codes have been set (does not mean some may show up as pending - some codes take 2 or more drive cycles to pop up). IF no codes set AND event is happening THEN computer may believe it is doing what it was designed to do.

 

I do not believe the speedo shuts down during this but when I drive it today will check if it persist. I am just about at the point to just change out the VSS.... Any where to buy one recommended?