D1 rev limit around 2k rpm

NigelDI

Member
Mar 29, 2022
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Hello all, I have a 96 discovery 1 that I have been daily driving for a little over a year. A few weeks ago the truck started to limit rev around 2000k. It does it while cold or warm in gear moving as well as stopped in park. Truck runs fine at idle, can still be driven up to about 50 mph but stinks like gas real bad. Plugs and wires are less than a year old and wires were quality. Just changed coils because they showed signs of heat. Holds good fuel Pressure and vacuum. Still tested for leaks with nothing changing. Only code it currently throws occasionally is a random misfire. I changed the MAF no difference. I pulled my cats down thinking they were plugged, open manifold it still limits around 2k rpm. I took it to a reputable master rover tech near me that has helped me out in the past. He plugged into it and we drove it around everything checked out electronically. He suggested plugging in another ecu, so I picked one up and plugged it in today and my problem still remains. I have a new set of Bosh 4 hole injectors I plan to put in it today.

Any thoughts or assistance would be much appreciated.
 
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WaltNYC

Well-known member
Mar 3, 2010
707
135
NYC
I'm guessing VSS. If you have a OBD device monitor the "vehicle speed". If I am right, your speed will shoot up to some crazy number above 100 mph and the truck thinks it is over the limit an retards timing. The bottom gauge on the device in the video was the vehicle speed. It is all over the place. (top is coolant temp)

The other way to rule out the VSS is to unplug it. You will lose the speedo and mileage odometer while unplugged but the problem should no longer exist.

 
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NigelDI

Member
Mar 29, 2022
8
0
80228
I'm guessing VSS. If you have a OBD device monitor the "vehicle speed". If I am right, your speed will shoot up to some crazy number above 100 mph and the truck thinks it is over the limit an retards timing. The bottom gauge on the device in the video was the vehicle speed. It is all over the place. (top is coolant temp)

The other way to rule out the VSS is to unplug it. You will lose the speedo and mileage odometer while unplugged but the problem should no longer exist.

That was tested they remain the same while driving. I wasn't sure if the VSS could be a culprit if it does it while siting in park not moving?
 

WaltNYC

Well-known member
Mar 3, 2010
707
135
NYC
I should read more carefully. You did mention that it behaves the same whether on the move or parked.

Sounds like a fueling issue. FPR? Pump? Injectors?
 
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Gordo

Well-known member
crankshaft positioning sensor, wiring to the sensor, or the teeth on the flex plate
Just fixed a similar issue last night on my sons 96 D1. Ours would rev to around 2500 and break up. Intermittent but what I found was the wires running to the CPS were dried up and bare clearly shorting out at times. I wired in a new plug and wires from the parts truck. The same plugs are used in the lights etc. running good now.
 

p m

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Staff member
Apr 19, 2004
15,617
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La Jolla, CA
www.3rj.org
Nigel, it is easy to inspect the teeth on the reluctor ring - just pop the inspection cover in front of the transmission, and turn the flywheel slowly using a large flathead screwdriver.
 
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boxster

Well-known member
Jun 1, 2009
443
88
Fallbrook Ca.
Hello all, I have a 96 discovery 1 that I have been daily driving for a little over a year. A few weeks ago the truck started to limit rev around 2000k. It does it while cold or warm in gear moving as well as stopped in park. Truck runs fine at idle, can still be driven up to about 50 mph but stinks like gas real bad. Plugs and wires are less than a year old and wires were quality. Just changed coils because they showed signs of heat. Holds good fuel Pressure and vacuum. Still tested for leaks with nothing changing. Only code it currently throws occasionally is a random misfire. I changed the MAF no difference. I pulled my cats down thinking they were plugged, open manifold it still limits around 2k rpm. I took it to a reputable master rover tech near me that has helped me out in the past. He plugged into it and we drove it around everything checked out electronically. He suggested plugging in another ecu, so I picked one up and plugged it in today and my problem still remains. I have a new set of Bosh 4 hole injectors I plan to put in it today.

Any thoughts or assistance would be much appreciated.
Hello all, I have a 96 discovery 1 that I have been daily driving for a little over a year. A few weeks ago the truck started to limit rev around 2000k. It does it while cold or warm in gear moving as well as stopped in park. Truck runs fine at idle, can still be driven up to about 50 mph but stinks like gas real bad. Plugs and wires are less than a year old and wires were quality. Just changed coils because they showed signs of heat. Holds good fuel Pressure and vacuum. Still tested for leaks with nothing changing. Only code it currently throws occasionally is a random misfire. I changed the MAF no difference. I pulled my cats down thinking they were plugged, open manifold it still limits around 2k rpm. I took it to a reputable master rover tech near me that has helped me out in the past. He plugged into it and we drove it around everything checked out electronically. He suggested plugging in another ecu, so I picked one up and plugged it in today and my problem still remains. I have a new set of Bosh 4 hole injectors I plan to put in it today.

Any thoughts or assistance would be much appreciated.
I agree with WNYC fuel related problem however you say the fuel pressure is good, maybe pressure regulator. Did you try a fuel filter?
 

discostew

Well-known member
Sep 14, 2010
7,706
1,015
Northern Illinois
Do you have a scanner? If so what is your Throttle Position sensor reading? Do you know if this is an advanced Evaps truck?
What happens to some of these trucks is a bunch of green fur starts growing out of the fuel tank pressure sensor. Because that sensor shares its reference voltage it pulls the TPS low. In the early stages of this failure it might not store a fault code. The truck just thinks your off the gas
 
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rover rob

Well-known member
Mar 29, 2016
273
56
upstate NY
Do you have a scanner? If so what is your Throttle Position sensor reading? Do you know if this is an advanced Evaps truck?
What happens to some of these trucks is a bunch of green fur starts growing out of the fuel tank pressure sensor. Because that sensor shares its reference voltage it pulls the TPS low. In the early stages of this failure it might not store a fault code. The truck just thinks your off the gas
stew didn't they switch to advanced evap in later 97 ? one of my 97s is advanced and the other is not.
 
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LRDONE

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Dec 3, 2020
336
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Michigan
If Throttle Position sensor fails in the "closed" position, the ECM will initiate a over-run fuel cut off at 1750rpms or more. I would most definitely check the TPS with live data and rule it out.
 

discostew

Well-known member
Sep 14, 2010
7,706
1,015
Northern Illinois
If Throttle Position sensor fails in the "closed" position, the ECM will initiate a over-run fuel cut off at 1750rpms or more. I would most definitely check the TPS with live data and rule it out.
I'm not saying the TPS has failed. I'm just asking what the TPS voltage is. Measuring that is free, and if It's what I'm talking about your 5V coming into the sensor is going to be low. So then the TPS output is even lower than that.
 

LRDONE

Well-known member
Dec 3, 2020
336
116
Michigan
I'm not saying the TPS has failed. I'm just asking what the TPS voltage is. Measuring that is free, and if It's what I'm talking about your 5V coming into the sensor is going to be low. So then the TPS output is even lower than that.
Correct, Which I believe a low sensor out put would indicate that the throttle plate is more closed than it should be. The TPS and MAF work hand and hand which I'm sure you already know. Any inconsistencies with the TPS compared to MAF the ECM will cut fuel at 1750rpm or more. I think you're right on with checking that 5v input first.
 
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Flyfish

Well-known member
Oct 29, 2004
1,402
212
52
St. Louis
Any inconsistencies with the TPS compared to MAF the ECM will cut fuel at 1750rpm or more.
The TPS seems logical except his comment about the strong gas smell. If fuel is being cut off, it would run lean and probably backfire. Seems like he’s losing spark instead of fuel which points at the crank sensor/wires etc.

TPS & crank sensor related seem like the best possibilities..
 
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