Cutting in and out at 70mph

[supersquid]

I was driving home last weekend from a Cycle Cross race and my 1996 Disco started to cut in and out on the hwy. The truck would surge up and down. The problem would last a few miles and then disappear. I suspect the fuel filter but want to get some other opinions. My truck does vibrate because the tire are out of aliment so the shaking might have contributed to this problem. Any other ideas what might cause this issue? Thanks

 

[singingcamel]

fuel filter is where i would start, cheap east fix..

 

[Bannon88]

fuel filter is where i would start, cheap east fix..

x2 on the fuel filter. The filter is probbaly beginning to clog and it will only get worse as the filter prevents the pump from delivering the volume of fuel your engine needs at around 70mph. I had a similiar problem and the fuel filter was indeed the issue.

 

[gibson04]

do a search on "vss", unplug it and see if it helps. if it clears up get a vss. unpluggin will cause check engine light to illuminate, however it wont cut in and out anymore if that is the solution. My truck usually runs its best when the check engine light is on!

 

[D Chapman]

It's probably the Mystery Miss. People have over the years experienced this and to date I don't think anyone has a known solution.

I had a 1999 D1 that did this pretty regular at interstate speeds. I changed/replaced/checked the following:
Plug
plug Wires
VSS
Coil Pack
Fuel Filter
Cleaned all engine grounds
Ran multiple computer diagnostics
Compression test

I stopped short of rebuilding the heads. The only other factor I could think of was a carbon issue.

You may search the board to see what others have done.

Good luck with it.

 

[MonLand]

My 1996 DI did something similar, however, it would not surge, just cut out and then work fine again.
If you can, put a gauge to check fuel pressure from your driver seat.
In my case the connector from the wiring harness to the fuel pump was bad. Took me about a year to finally end up with the truck not restarting to be able to figure what the problem (can't fix something that works) was.
I feel lucky that I did not get stranded on the highway, instead, it decided to quit completely on a mall parking lot (I guess driving put enough vibration to wiggle the connector enough to make the fuel pump run from time to time and keep enough fuel coming for the engine to run).

 

[ptschram]

I had a problem with the fuel pump in my LWB that drove me nuts! At first, the voltage would drop when the pump was connected. Took me far too long to see that the pump was shorted to ground. Fixed that...

Then, I had power supply problems so I rewired it all the way from the relay to the pump. Fixed that...

At breakfast during the first rain in months. Go out to truck, no start. Make it home, check power to pump-yep, swapped another pump in. Fixed that...

Driving down the road the other day, damned thing quit! Got out, wiggled the wires, started back up... Drove a coupla blocks, quit. Wiggled wires. Drove to the bank. On the way out of the bank, truck quits. I pulled out my trusty jack knife, lopped off the ground wire down to where it wasn't corroded, twisted the wires together, it got me home! I've since connected the wires a little better.

It was a nightmare getting this truck to run consistently!

Good luck.

 

[Bannon88]

My 1996 DI did something similar, however, it would not surge, just cut out and then work fine again.
If you can, put a gauge to check fuel pressure from your driver seat.
In my case the connector from the wiring harness to the fuel pump was bad. Took me about a year to finally end up with the truck not restarting to be able to figure what the problem (can't fix something that works) was.
I feel lucky that I did not get stranded on the highway, instead, it decided to quit completely on a mall parking lot (I guess driving put enough vibration to wiggle the connector enough to make the fuel pump run from time to time and keep enough fuel coming for the engine to run).

One problem I had with checking the pressure at the fuel rail was that it read just fine 33-35psi. However if the filter is getting clogged, the pump can only supply enough fuel volume up until a point, due to the filter clog.

In the TS's case it seems to be around 70 mph, then the volume of fuel begin delivered is simply not enough to meet the engines demand.

 

[D Chapman]

.....I swapped MAF's, too

I don't buy the fuel pump issue. Maybe it's this guys problem, I don't know. But for the others who had this problem it does not make much sense. In fact, I think a few people changed the pump but it was a waste.

If it's anything like mine, it would happen anywhere from 45mph to 75mph. Some times it would miss once and be fine for a 500 mile trip. Other times it would miss repeatedly from the house to the store. This went on for months and months. If it were fuel starvation you would have backfiring, popping, stalling, etc.

I'm still determined it was either carbon or possibly a bad converter.