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Steveastrouk

NAS spec 4.0 loses power then it comes back on restart

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Hi

My son rolled his pride and joy, his 1997 Disco 1 NAS spec 4.0 while recovering the car from a desert track where he'd had to replace a draglink in the field. He let it sit for a few days for everyhing to drain back into the right places, then was forced to leave his school because of Covid and come home. 

On the 2000 mile return trip he kept getting weird powerlosses, which we couldn't  resolve, they didn't correlate with hills, high speeds or anything else. He was in such a bad state, his mum and I drove out 500 miles to meet up with him and help. I experienced the same thing as he did. The weird thing here is that when we pull off the road, turn off the ignition and IMMEDIATELY turn it back again, the damned thing purrs like a kitten and we're on our way. 

NOW, full discloseure,  fairly recently he'd burned out his fuel pump (student cash flow crisis- ran it dry) and replaced it with an after market pump.  I'm still seeing decent rail pressures, and no leakback when the ignition is off, but we have that as a contender.

Next, the local autostore ran the OBD on it, and we get P0451 and P1316 - I'm very suspicious of P0451 - fuel pressure sensor fault. Would that give us the symptoms ? There are defintely wire issues back there.

Thanks for any input you can give us.

Steve

 

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Rule out the easiest first, what does the fuel filter look like? If he ran the tank dry there's a good chance it sucked sediment up, that might have expedited the demise of the pump and clogged the filter. That would give low fuel pressure and could cause the fault code... In theory. It would normally be uniform in power loss.

I believe the pressure sensor is on the fuel rail running around the base of the plenum on the engine (I'm assuming you're on GEMS as a 1997) so that is likely where the ECU is getting its reading from. It might be a sensor fault but I doubt it if you're getting the loss in power to match. 

I would also check the air filter as being upside down might have sucked debris that was sat on the bottom of the housing into the element. I once had a whole (very dead) bird in mine, that didn't aid power. 

Have all fluids been checked since the roll? How did they look?

Have the electrical connections to things like the ECU and battery been checked? They can come loose and give very weird behavior, especially multi-pin plugs. Have the connectors on the new pump been checked, they might have worked loose or rubbed on something and give an intermittent short.

It might be an idea to fit a low pressure filter on the return line of the fuel rail so you can see both the volume and colour of what's coming through.

Don't rule out anything just because it's not related to rolling the car, sometimes stuff just happens in quick succession.

This hopefully gets you started. Let us know what you find.

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He did both fuel filters for sure. Oil looks OK, Battery is still nicely tied in. Checked the ECU wires too. Air filter needed changing, that was done.

I think its the intermittency that gets me. Driving it back, we had a couple of hours with nothing, then not more than 20 minutes of driving between issues.

It might've correlated very very slightly with the level of fuel in the tank, I don't know.

<edited>

Now he adds that JUST before he had the rollover that he had one episode of this, so that event might not have been the trigger. Sorry, wasn't aware of that earlier. There was a lot of oil in the filter after the roll.

Would O2 sensor failures give us an issue like this.

 

 

 

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9 hours ago, Steveastrouk said:

Would O2 sensor failures give us an issue like this.

Unlikely I'd think.

Does the issue correspond with the engine being hot (as in, it's OK when it's cold but gets worse as it warms up)?

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Reckon your pump is bad, or connections not made properly.

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I once had an intermittent fuel pump cut out issue on my RRC. Turned out that the wiring loom was shorting on the exhaust when cornering. Point being that it could be something daft like that so it’s worth eliminating the basics first.

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5 minutes ago, Bigj66 said:

I once had an intermittent fuel pump cut out issue on my RRC. Turned out that the wiring loom was shorting on the exhaust when cornering. Point being that it could be something daft like that so it’s worth eliminating the basics first.

Going to go under it and explore tomorrow.

What gets me is that it is instantly fixed by turning off the ignition. I need to wiggle nothing to make it work.

Shorts are entirely possible.

 

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If it's debris in the tank it could be being sucked up and sticking to the pump intake, when you shut it off the pump stops sucking and it drops back to the bottom of the tank.

Friend of mine had that with the oil pickup in an old car.

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I would check the fuel system again. The symptoms do sound like either sediment in the system, or maybe even a hose internal collapse. Could even be a faulty filter or pump ?

Is the fuel filter an inline one ? If so, has it been installed the right way round, as some of these flow better one way than the other. I would fit ANOTHER new quality one anyway. Do not refit one if you do find one is installed the wrong way round.

Is it possible to run the fuel pump independently, and with hose connected at the engine end to discharge into a bucket, or even back into the fuel filler, to see if the flow peters out ?

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I'm re-thinking the lambda sensor question.. if the thing has been upside-down and spat oil down the exhaust it could've coated/damaged the sensors, I'd hope that wouldn't be enough to cause a major problem but it's Lucas so all bets are off... you can clean the sensors by removing them and heating the tip cherry red with a blowlamp, may or may not help but it's free.

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Posted (edited)

So dad (me) finally got to drive the thing extensively today - another suggestion received elsewhere was a glitchy VSS, so I removed that for a try out, and still no dice. What I experienced with it though wasn't "loss of power", I had outright misfiring. Bringing the car to the side of the road, and idling it doesn't return the power. Switch off, and immediately restart - bang, we're off again.

I'll clear the codes on the OBD and try tomorrow.

Thanks for all the ideas, I'm still leaning to the fuel pump, going to underneath and look at all the wiring tomorrow.

Edited by Steveastrouk
Added note

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Also, I notice the thing has a VERY high idle, in Park - like 2800 RPM. Could that be a symptom ?

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Check for vacuum leaks then, all the hoses.

Did the engine run at all when upside down?

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9 hours ago, Steveastrouk said:

Also, I notice the thing has a VERY high idle, in Park - like 2800 RPM. Could that be a symptom ?

I'd say so, that's got to be a vacuum leak, stuck/clogged idle valve or other damage to the top end (EG throttle linkages / plenum).

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THAT'S an interesting idea. Are there are procedures for vacuum leak testing - I've vacuum bled brakes, but I have never looked  engine systems and vacuum,

Thanks guys

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The sketchy way to identify vacuum leak on the intake system is to spray something flammable near joins and see if the revs rise. Easy Start or something like that would be best but I've heard of people using brake clean.

The right way... no idea.

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For it to be revving up that much, it has to be a hose off really, i.e. a major leak.

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Indeed, 2800rpm is more than a high idle, that's a healthy cruising speed!

Checking for vacuum leaks by spraying petrol or carb/brake cleaner around is the usual way (after visual inspection), just be careful and have an extinguisher on standby!

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CLEVER ! Thanks guys. We're about to get whacked by the tail end of that hurricane Isias tonight, so that's a tomorrow project, weather permitting.

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Not vacuum leaks, blew something nice and volatile at it, didn't twitch except when I blew a sniff in the inlet itself.

Airbox and environs on the list to look at tomorrow.

No sign of the throttle linkage sticking or anything simple

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What about blocking off the stepper idle valve on the back of the plenum? That's the only other thing that can allow air in.

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Will try that in the morning. It also occurred to me, that given him rolling the bloody thing, I don't know if the plenum has crud in it too.

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