BarryA

BarryA

Member
The front air springs on my P38 are behaving in a rather strange manner. The rear will lift to its normal height but the front will keep lifting past the correct height until it reaches a maximum at which point it stops the compressor and drops everything back down and begins the cycle all over again. I’ve put my nanocom on it and when going up it shows the front valves closing at the right height but it keeps lifting. I read something which suggested swapping NRV might help but this made no difference. If you open a door while the compressor is running it stays at the same height. Any suggestions?
Cheers.
 
BarryA said:
The front air springs on my P38 are behaving in a rather strange manner. The rear will lift to its normal height but the front will keep lifting past the correct height until it reaches a maximum at which point it stops the compressor and drops everything back down and begins the cycle all over again. I’ve put my nanocom on it and when going up it shows the front valves closing at the right height but it keeps lifting. I read something which suggested swapping NRV might help but this made no difference. If you open a door while the compressor is running it stays at the same height. Any suggestions?
Cheers.
Click to expand...
If the front valves are definitely closing and it keeps rising, I would look at the solenoid valve O rings. Also, Nanocom may show that the valves are closing as a result of power being cut off but there is no feedback to show that they have actually closed.
Final thought, unscrew the silencer at the rear of the valve block and look for white powder.
 
BarryA said:
The front air springs on my P38 are behaving in a rather strange manner. The rear will lift to its normal height but the front will keep lifting past the correct height until it reaches a maximum at which point it stops the compressor and drops everything back down and begins the cycle all over again. I’ve put my nanocom on it and when going up it shows the front valves closing at the right height but it keeps lifting. I read something which suggested swapping NRV might help but this made no difference. If you open a door while the compressor is running it stays at the same height. Any suggestions?
Cheers.
Click to expand...

If you don't have a Nanocom or similar you'll need to download EAS unlock from Storey Wilson's website. If you PM Datatek than he may be willing to knock you up a cable at a decent price, although shipping to the UK is probably more than the cable these days.
 
Grrrrrr - I’ve got a nanocom and it’s able to see what’s going on with the EAS. Datatek - I’ll open up the valve block this week and check the solenoid valve orings. I did unscrew the silencer and it’s clean, not signs of power and the air dryer was replace a couple of years ago.
 
The fact it freezes when you open a door is correct behaviour so thinking it may not be a leak but the height sensors not reading correctly. Nanocom should show target and actual heights as it rises. You can record a trace as a csv file to use on a computer.
 
I recently had similar behaviour on mine. Front sensor turned out to be the issue. Changed it and - touch wood - everything now ok.
 
Sorry for the delayed response. I’ve attached a text file with the output from the nanocom showing 2 full cycles. There are no faults showing. In the last couple of days I’ve also tried a spare valve block and driver neither of which made any difference. I had to replace a rear sensor several months ago (the one with the lower values) but I recalibrated afterwards.
 

Attachments

  • EAS Test2.txt
    46.2 KB · Views: 119
You rear left & right target values should really be closer together. General the system works better if Front L <--> R are within two bits of each other, and rear less that 4-6 bits different to each other.

At lines 25-26, it appears as if the fronts dropped by 15-20 bits, but the valves were closed ? At same time the rear valves opened along with the exhaust. Similar weirdness further down the file. Have you had the valves off the block ? If so did you definitely get them back in the correct positions ?

also the compressor was running all the time. This implies the diaphragm valve was engaged, so exhausting air cannot work correctly.
 
The rear sensor was a cheap one to be fair and prior to the change the values were closer together. I’ll try getting a pair sorted for the rear to see if that helps but while I wait on them coming I’ll try setting the values closer together to see if that makes a difference. The compressor definitely stops when the front drops and then restarts when it’s down.
As for the valves being in the wrong location, the rears picks up first as I believe it should and it showed the same behaviour with a spare valve block and driver.
 
Could just be Nanocom delays, so the recording is off !! Before buying more sensors, you might find that loosening the height sensor bolts slightly, allows just enough movement to get the readings closer ??

To do it, lift the rear up, and put identical blocks ( 2-4 inches will do) under the bump stops. Then lower onto the blocks & check the readings in Nano. Then try tweaking the sensors to get the readings as close as possible.

Took another look at your recording. See attached Excel file where I have coloured the valve status to make it easy to see when the system is raising or lowering. It seems it's repeatedly flipping between trying to adjust Fronts followed by Right Rear. The RL hardly ever adjusts. I'm wondering if you have internal leaks in the valve block, or if this is just the sensor coupled with Nanocom recording bollocks ?

I certainly do not trust this recording so far. (will do similar on mine tomorrow & compare.)

Here the fronts are only open briefly, but it drops loads ?
upload_2022-11-13_18-32-17.png


Here the front rises again, followed by a failure to raise rear right . . . . but fronts continue to rise ?
upload_2022-11-13_18-34-18.png
 

Attachments

  • upload_2022-11-13_18-33-9.png
    upload_2022-11-13_18-33-9.png
    7.6 KB · Views: 76
I spent quite a bit of time tweaking the position of the sensors to bring the rear values closer together (eventually within 3 bits) and the system was still behaved the same. So having tried valve block, driver, calibration etc I realised the only thing I hadn’t tried was the EAS ecu. I managed to get my hands on one today and it seems to have solved the issue. Still need to do a full calibration but I put it the standard height values I had been using and it came up to height and stayed there. Fingers crossed it’s solved.
 
BarryA said:
I spent quite a bit of time tweaking the position of the sensors to bring the rear values closer together (eventually within 3 bits) and the system was still behaved the same. So having tried valve block, driver, calibration etc I realised the only thing I hadn’t tried was the EAS ecu. I managed to get my hands on one today and it seems to have solved the issue. Still need to do a full calibration but I put it the standard height values I had been using and it came up to height and stayed there. Fingers crossed it’s solved.
Click to expand...
Well done, there seems to be a spate of EAS ECU failures, normally they seem to have been reliable.
 
Might be interesting to check for dry joints. The ECU was operating to some extent, so maybe the sensor inputs, A-D converters or dried out capacitors like other old ECU's ?

But at £25 for a second hand replacement probably not worth the hassle.
 
BarryA said:
I spent quite a bit of time tweaking the position of the sensors to bring the rear values closer together (eventually within 3 bits) and the system was still behaved the same. So having tried valve block, driver, calibration etc I realised the only thing I hadn’t tried was the EAS ecu. I managed to get my hands on one today and it seems to have solved the issue. Still need to do a full calibration but I put it the standard height values I had been using and it came up to height and stayed there. Fingers crossed it’s solved.
Click to expand...
Nice one!
Fingies crossed :cool:
 
pwood999 said:
Might be interesting to check for dry joints. The ECU was operating to some extent, so maybe the sensor inputs, A-D converters or dried out capacitors like other old ECU's ?

But at £25 for a second hand replacement probably not worth the hassle.
Click to expand...
Corrosion from a damp interior is another possibility.
 
Datatek said:
Well done, there seems to be a spate of EAS ECU failures, normally they seem to have been reliable.
Click to expand...

I guess most are 20+ years old now. Jiggled and alternatively baked and frozen with damp. How long do the components last?

Soneone once talked of making an Aduino replacement. I'm not sure that would be robust enough but the idea was right, unless some clever sausage knows how to refurb them.
 
Grrrrrr said:
I guess most are 20+ years old now. Jiggled and alternatively baked and frozen with damp. How long do the components last?

Soneone once talked of making an Aduino replacement. I'm not sure that would be robust enough but the idea was right, unless some clever sausage knows how to refurb them.
Click to expand...
The semiconductors last a surprisingly long time, it's electrolytics that die. I don't know the Arduino, but the software to control the suspension would be the challenge, much easier to repair the existing ECU. Sometime ago there was a guy who proposed building a HEVAC replacement, I was pretty sure he had not realised the complexity of the code needed to operate all the functions, he has never returned to my knowledge so I would guess that the challenge defeated him.
You can buy off the shelf air suspension control systems in the USA.
 
You must log in or register to reply here.

Similar threads

Flossie
P38A Eas issues
2
Replies
22
Views
1K
Datatek
Datatek
B
P38A P38A 1996 4.6 Auto HSE EAS slow to lower and rise + random height change to extended height + compressor running too frequently.
Replies
9
Views
1K
Datatek
Datatek
D
L320 suspension query
Replies
6
Views
442
Graculus
Graculus
feyniriel
P38 EAS problems
Replies
18
Views
1K
pwood999
pwood999
S
Height suspension / sensor issue - can't calibrate
Replies
3
Views
1K
Graculus
Graculus