Technical X250 2.3JTD Fuel pressure spiking P0093, surging idle

[aurumdeus]

Hi,

I've got a 2.3 JTD 120, engine code F1AE0481D.

I've been having issues with two things. Firstly the fuel pressure. When I start and idle everything runs perfectly, and if I slowly change the engine speed the requested and actual fuel pressures track each other accurately. If I blip the throttle the requested and actual fuel pressure spike up, then the requested fuel pressure immediately drops down again while the actual fuel pressure remains high. It stays that way for around 10 seconds, gradually falling down to meet the requested pressure.

Idle is around 450 - 500, throttle blip sends it to around 1000, and when the requested drops back down to 450 ish the actual remains easily around 900 for a while. I can see the duty cycle on the pressure regulator remaining higher than at idle (42% at idle, 45% when elevated), so it would appear that the ECU is deliberately keeping the fuel pressure higher than it wants. It's just had a new fuel filter and a new pressure control valve. If I turn the engine off and do an active test to actuate the regulator then I can hear and feel it clicking open and shut. Each time the fuel pressure remains elevated for more than a couple of seconds it sets P0093.

Has anyone encountered this before? I've tried running a reset of learned parameters but that didn't change anything.

The second issue is with the throttle body. It was head due to the windscreen drain pipe detaching and leaking onto the old actuator. I've now replaced it (along with the adapter cable), and it's mostly fine. No shudder when turning off the engine, actuates correctly in test mode. However when the engine is at idle it's causing a surging, it gradually shuts, nearly stalls the engine, then shoots open, and repeats. The EGR also actuates in time with this. EGR is vacuum actuated, unplugging the pipe changes nothing so it's not caused by the EGR. Unplugging the MAF stops it. MAF readings do rise and fall as the valve opens and closes.

No error codes relating to this issue. In both cases it seems like the engine is doing what the ECU is asking of it, I'd just not sure why the ECU is asking it to behave in this way.

Has anyone encountered either of the above behaviours?

Thank you for any input

 

[Anthony489]

Hi aurum

I can only postulate a couple of things.

The P0093 generic code means a sudden drop in fuel pressure, which could be a massive leak (not in your case !) or a restriction in flow. This is a bit of a puzzle given that your problem appears to be pressure that is too high. I don't know whether the delay in the pressure dropping after a high demand is a fault or normal behaviour. It might be worth trying a new fuel pressure sensor unless you can be certain that it isn't playing up.

The throttle body and the EGR valve perform a "double act" to control the EGR process during idling and light load operation. As the Throttle body (TB) closes, it enhances the partial vacuum in the inlet manifold which encourages the flow of recirculated exhaust gas. At the same time as the ECU closes the TB, it opens up the EGR valve (via the solenoid valve and vacuum lines). I'm wondering if the EGR valve (or its filters, pipework etc) is blocked, so as the throttle body closes the engine is starved of air and begins to stall, at which point the ECU "panics" and opens up the throttle body again. Also worth checking the rubber vacuum lines from solenoid valve to EGR are in place and free of splits.

 

[aurumdeus]

Hi Anthony,

Thank you for the suggestions. That's a good point re the EGR flow. There is a change in sound when I unhook the vacuum tube going to the EGR so something is occurring, but whether its enough is another question. The vacuum line is new as it had previously split and detached from the solenoid, which I imagine meant the EGR was permanently closed for a long period of time.
I'll see what I find in that route.

Also a good idea re the fuel pressure sensor. I suppose it's possible that the reading is somehow lagging when the pressure falls rapidly. The live data doesn't update that rapidly so it's possible that there is a very brief loss of pressure at some point, but it would have to be for less than half a second or so and has never occurred at the same time as a data point update, so it seems improbable if not impossible.

I'll update when I've explored those two routes.

 

[fruchty]

Did you find the cause of high fuel pressure?