P38A Is my mojo rising..... or do I need a new Driver Board?

[DarthDude]

Hi Rangie folks..... here's the situation:-

Car is on pretty decent valve block and airsprings. Parked up with battery disconnected, the rears will drop before the front and take about 10 days to go from normal height to the bump stops. That's good enough for me. The reservoir and dryer are also in good shape because after said 10 days, there's still enough stored air in them to raise the car to normal height immediately upon starting the car up.

The ride height has been calibrated with my home made calibration blocks and and Faultmate MSV-2 and the values are (a) fine and (b) all within 2 data bits of each other.

The ISSUE is that when the car is run any length of time, or parked up with the battery connected, it RISES by maybe an inch and a half, and if parked up with the battery connected for say 3 days, it starts to drop and the air in the reservoir is all gone and the poor ole pump has to run and run and run in order to get the car back to its proper height.

Again, with the battery DISCONNECTED, it doesn't rise when parked up, it just settles down onto the bump stops after about 10 days.

My GUESS is that the driver board is leaking some current into the inlet and airspring valves, allowing air into the airsprings when it shouldn't. This raises the car. When the ECU goes to check the ride height, it drops the car again. When the car is parked, it does this every however-often-it's-supposed-to by opening the airspring valves and exhaust valves to bring the car down to the height it's supposed to be, whereupon the faulty driver board then allows more air to leak from the reservoir into the airpsrings, raising the car again until the ECU wakes up again and drops the car one more time... and the cycle repeats until the car has used up all the air in the reservoir and then drops due to the none-too-airtight-but-still-pretty-acceptable (Sh!tpart) valve block.

Am I on the right track here, or should I look elsewhere before spending megabucks on a new driver board?

Cheers!

 

[backinblack]

I'm not a P38 person so it's a general question. What make you think it's not just an air leak somewhere and with the battery connected it's trying to raise the car with the air in the tank until it runs out. With the battery disconnected it can't use the air in the tank so just goes down and the air is still there when you reconnect the battery?

 

[DarthDude]

Oh it's definitely leaking because the rears drop first.... but the rate of the drop is so slow- as I say 10 days to go from normal height to bumpstop I'm GUESSING it's unlikely to run out of reservoir air in 3 days if all it's trying to do is maintain the proper ride height.

Plus that doesn't explain why the car rises by easily 1 1/2 inches with the battery connected but doesn't with it disconnected. Maybe a little, but I'd have thought 1 1/2 inches is a bit excessive for an ECU adjustment overshoot.

But thanks for that. Maybe I WILL just go and audit the rear airspring valves (I know one of them has a slightly stripped thread for the self tapping screw holding the top of the valve to the valve body) before I try anything else so please, keep them coming. Any thoughts welcome- I really need alternative points of view like exactly yours to keep testing the theory before I go and spend £170 on a new driver pack. Plus shipping. Plus tax. Ouch.

 

[tomcat59alan]

Oh it's definitely leaking because the rears drop first.... but the rate of the drop is so slow- as I say 10 days to go from normal height to bumpstop I'm GUESSING it's unlikely to run out of reservoir air in 3 days if all it's trying to do is maintain the proper ride height.

Plus that doesn't explain why the car rises by easily 1 1/2 inches with the battery connected but doesn't with it disconnected. Maybe a little, but I'd have thought 1 1/2 inches is a bit excessive for an ECU adjustment overshoot.

But thanks for that. Maybe I WILL just go and audit the rear airspring valves (I know one of them has a slightly stripped thread for the self tapping screw holding the top of the valve to the valve body) before I try anything else so please, keep them coming. Any thoughts welcome- I really need alternative points of view like exactly yours to keep testing the theory before I go and spend £170 on a new driver pack. Plus shipping. Plus tax. Ouch.

Pm me a photo of the bit that's stripped the threads,@RangeRoller dt sent me some bits and I'll have a look to see I've got what you need.

 

[wammers]

If the car rises whilst parked the inlet valve from tank to fill port is leaking. Nothing to do with driver pack. Which is a slave of the ECU.

 

[backinblack]

If the car rises whilst parked the inlet valve from tank to fill port is leaking. Nothing to do with driver pack. Which is a slave of the ECU.

OP says it doesn't rise with battery disconnected. IMO leaking valve would not be battery dependent?

 

[DarthDude]

Pm me a photo of the bit that's stripped the threads,@RangeRoller dt sent me some bits and I'll have a look to see I've got what you need.

Will do buddy- thanks. Let me try just buying a different self tapping screw and see if it'll torque up sufficiently then. Sometimes you can get away with just using a different screw with a slightly different thread. I'll let you know how it goes.

 

[DarthDude]

If the car rises whilst parked the inlet valve from tank to fill port is leaking. Nothing to do with driver pack. Which is a slave of the ECU.

Yeah I thought of that first.... but there's a difference- it rises when the battery is connected but DOESN'T rise when the battery is disconnected.

If it was a mechanically leaking NRV or inlet valve then it wouldn't matter if the battery was connected or not, no?

But this is great stuff guys... keep 'em coming!

 

[wammers]

Yeah I thought of that first.... but there's a difference- it rises when the battery is connected but DOESN'T rise when the battery is disconnected.

If it was a mechanically leaking NRV or inlet valve then it wouldn't matter if the battery was connected or not, no?

But this is great stuff guys... keep 'em coming!

Fault in your ECU then. Or delay relay.

 

[DarthDude]

ECU maybe... but how would a faulty delay relay cause the car to rise?

 

[wammers]

ECU maybe... but how would a faulty delay relay cause the car to rise?

It switches the ECU on and off, if the ECU has no power to it it cannot do anything.

 

[Gord Wedman]

"and if parked up with the battery connected for say 3 days, it starts to drop and the air in the reservoir is all gone and the poor ole pump"

It drops at all four corners, not just the rear, and this takes less than 10 days?
If the rear drops because of leaks but the front only drops when the battery is connected, ie. no leaks in front bags, it would suggest valves are being held open slightly. Can you measure current drain at the battery? I think when the car is fully asleep this is less than 50 milliamps. If you see 500 that would suggest something is on. You could then disconnect modules to see which one is drawing current.

 

[backinblack]

Does the P38 self level upwards?

 

[marjon]

Does the P38 self level upwards?

No.

J

 

[backinblack]

But the OP's does if the battery is connected

 

[DarthDude]

It switches the ECU on and off, if the ECU has no power to it it cannot do anything.

Well yes, but that still implies that the rising of the Solihull Horror is commanded by the ECU, which may well be faulty but it's still hard to see how a faulty delay relay will itself cause the rise.

I sure hope it's not the ECU....... because Faultmate is married to it, I can't just swap another one in there to check for it and expect the Faultmate to work with the replacement.

Ok... let's leave the ECU to the last suspect to be examined.

 

[DarthDude]

"and if parked up with the battery connected for say 3 days, it starts to drop and the air in the reservoir is all gone and the poor ole pump"

It drops at all four corners, not just the rear, and this takes less than 10 days?
If the rear drops because of leaks but the front only drops when the battery is connected, ie. no leaks in front bags, it would suggest valves are being held open slightly. Can you measure current drain at the battery? I think when the car is fully asleep this is less than 50 milliamps. If you see 500 that would suggest something is on. You could then disconnect modules to see which one is drawing current.

It drops at all 4 corners with the rear leading the way. What happens is that if I leave the car parked with the battery connected, it'll rise by at least 1 1/2 inches. Pretty much wading height, and it'll stay there for around 3 days. I haven't staked out the car to watch it continually for the whole 3 days to see if it drops to normal height periodically when the ECU wakes up and then starts rising again when the ECU falls asleep, but everytime I check it, it's high. After 3 days, it starts to drop from wading height, suggesting to me that the reservoir is empty and there's no air left to leak into the airsprings and nothing left for the ECU to raise it back to normal height.

By contrast, when the battery is disconnected, the car stays at normal height and then starts gradually dropping led by the rear. As I say 10 days from normal height to bumpstop at the rear.... but as soon as the battery is reconnected and the engine started, it comes right up to normal height immediately, suggesting that the reservoir has kept enough air over the 10 days to do the job as opposed to running out of air after 3 days with the battery connected.

To me, that strongly implies something electronic is going on and that there's only 2 suspects- the driver pack and the ECU.... and I sure hope it isn't the ECU.

Ouch.

 

[DarthDude]

But the OP's does if the battery is connected

No it doesn't self level- it goes well above the level it should be at. This is what has me thinking that the rise is due to whatever's wrong with it... and its self levelling- downwards is what keeps venting air out of the system and drains whatever is in the reservoir.

 

[wammers]

No it doesn't self level- it goes well above the level it should be at. This is what has me thinking that the rise is due to whatever's wrong with it... and its self levelling- downwards is what keeps venting air out of the system and drains whatever is in the reservoir.

Self level does not drain the tank. But a leaking fill/vent gallery inlet valve will cause the car to rise even if the battery is disconnected. Think you need to learn a bit more about how the system works to be honest.

 

[DarthDude]

Self level does not drain the tank. But a leaking fill/vent gallery inlet valve will cause the car to rise even if the battery is disconnected. Think you need to learn a bit more about how the system works to be honest.

Thank you. That's what I'm doing here- trying to learn.

The point is the car DOESN'T rise when the battery is disconnected, therefore no inherent mechanical leak on the inlet or airpsring valves, except for a known, minor, one on the nearside rear. Air stays in the reservoir 10 days, easy.

It only rises when the battery IS connected, therefore some current is going to the inlet and airspring valves. Hence the suspicion falling on the driver pack and- yes- ECU.

When the ECU wakes up periodically, it realises the car is too high and self levels DOWN to the proper height by venting air out of the airsprings, whereupon it goes to sleep again and whatever causes the car to rise continues to fill the airsprings with air from the reservoir until the ECU wakes up again, realises it's too high again, self levels again by venting air out of the airsprings again and goes to sleep again whereupon more air leaks out of the reservoir into the airpsrings, raising the car again until the ECU wakes up again, realises it's too high again and self levels DOWN again and air leaks from the reservoir into the airsprings again....etc etc etc until the reservoir is empty after 3 days.

Makes sense? So what am I missing here? The thing that makes me hesitate about the driver pack is the fact that there's no permanent 12v supply to it. Whatever power it gets comes from the delay relay and it needs power if it's somehow half opening the inlet and airspring valves.