I've got an interesting hiccup I can't seem to sort out. After warming up and driving some distance, I get a situation where the engine bogs down then recovers. I loose power during these episodes. So it's hard to maintain speed. It's not all the time. Does it mostly after driving about 10 miles or so. Doesn't do it every time I drive it and it doesn't throw codes every time either. The condition is very precise. Very rhythmic. It doesn't slowly loose it, it cuts right off and right back on. Which leads me to believe it's something electrical not fuel. See link for video while driving.
https://photos.app.goo.gl/RCJ9JKLK5aBpG9SQ6
It's not a transmission issue because it happens in all gears at all speeds.

1997 4.0 Auto
160k miles
Good compression all cylinders. No overheating

Codes I've gotten: P1313, 1316 and also some cyl specific ones before I did a full tune up. Now I get the general misfire codes

Parts I've changed: Plugs, Wires, all ignition coils, fuel pump, filter ( before it threw IGN codes I thought it may be starving for fuel) a crank position sensor along w a visual of the teeth on the flywheel,and finally out of desperation I put a known good ECU in. Still the exact problem.

I thought VSS for awhile, but there's no wonky speedo. Could a bad injector (s) cause a stall of this precision/rhythm?

 

I’m definitely no pro on this, but I doubt that one failing injector would cause that kind of power loss. I think you would get a miss on that cylinder, but you’re losing a lot of power. Generally a failing Crank Position Sensor would cut out completely. I’m not sure that they could do this. Also, I’m not sure what a failing Cam Position Sensor would do. Some kind of other failing sensor? I’m not sure if a failing upstream O2 sensor could tell the ECU to cut that much fuel. You’d think that a bad wire wouldn’t wait for 10 minutes into the drive to show itself. As I said, I’m no pro on this. I’m just throwing out a few thoughts as they come to me.

 

Thanks man. You're thinking is like mine. I corrected my post as I did replace crank sensor. I had forgotten about that. I would think a cam sensor failing would throw cam sensor codes. At least I hope it would.

 

How is your battery & alternator?
Extra grounding never hurts.

 

I noticed your video shows the engine is not yet at full temp. Does it happen after the engine is up to temp? or only during the heat-up cycle? Maybe ECU is flipping to limp mode. Maybe loose wire(s) or corroded connector(s), or low voltage like hrh suggests. My mechanic says low battery voltage can cause random OBD codes and be hard to troubleshoot.

 

Battery voltage is normal. Voltage is monitored constantly via Ultragage.Alternator hasn't given me a a reason to believe it's got an issue.
Engine temp doesn't seem to directly affect the issue directly. No it doesn't happen when it's cold. That's true. But it could be at 150 and start the issue, or 180. What does seem to do it is total time driven. For example, I can drive all over going to the store, run errands, stop go traffic etc. It's fine. Zero issues. Starts every time. Idols perfect. But if you take it on a longer hwy or two lane road then you will probably get the issue to come up.

 

Read that you replaced the Crank Sensor. How was the wiring to the crank sensor? Those wires can get quite crispy even inside the loom. Replaced them with some that was made for high temp environments. Kinda looks like what you would find going to oven elements.
Was able to pull the connector, once unplugged from the sensor, up and soldered the splices together. IIRC, the connector is the same as the one used on the indicator lamps.

I mention this as mine would cut out once in a while as I was going around exit ramps. Ended up being the crank sensor / wiring / mounting puck. Didn't always throw codes.

 

VSS. I am 90% sure. It sends a bad signal to the ECU to make it believe it is going super fast (like 120mph, which we all know is dreaming, but, you know, we all dream). The engine ECU retards timing to protect the engine.

Hook up a live data obd and watch the MPH reading. You'll see in this video what I mean.

https://landroverforums.com/forum/di...eed-ecu-79498/

 

Even though my speedometer is always steady? Every thread I read on failing VSS the speedo is reading erratically

 

Ill echo the above posters, VSS for sure.
Ive had 2x discos with bad VSS and both had rock solid spedo while doing the erratic cutout.
Best price ive found on them is : https://www.ebay.com/itm/182629130382