So I got stuck with a job I didn't really want in the first place and now its giving me grief as I knew it would, Its a 2006 Volvo FE 7.2 litre straight 6 (Deutz) D7e and it come to me from a new unknown customer with a lack of power and after a visual check and a code read it showed an active fault code Mid 128 Psid 96 Fmi 1 which in a nutshell is low rail pressure it had a slightly extended crank and live data showed supply pressure at a steady 5.5bar @ idle and rail pressure of 400 bar but not exactly steady, the visual check showed a new genuine pre filter and the main filter cap looked like it had recently been disturbed plus it had a brand new looking rail pressure sensor, at some point in its 250k miles its had a replacement commonrail with relief valve and both high pressure pumps and regulator but none of those looked recent. At this point with staffing issues and a heavy workload added to the fact it had been played with and an unknown customer I politely tried to swerve but to no avail.
After failing to get rid I decided to see what the rail pressure sensor was seeing and its 5v supply and look at the fuel pressure regulator pwm with a trigger on no 6 injector which is furthest from the flywheel on this engine, this is what I got
Ignore the bit at 41 seconds as my helper hadn't quite let the engine stop before turning the ign back on and it fired back up before being shut down again lol,
Here is a snapshot from the file above at idle speed which shows the uneven humps
This system has 2 pumps that feed the rail the pumps are run off the cam which has a triple lobe for each pump so there are 6 operations per 720 degrees and its clear that 1 of the pumps aren't contributing as much as the other.
At this point I needed to Id the bad pump so I disconnected pump 1 (nearest flywheel) from the rail and tried to start the engine but it failed to start, here is what I captured
From this its clear the low pulse is missing indicating no.1 pump to be at fault so I next reconnected one and disconnected 2 only this time the engine started right up... this is the capture
This was during the cranking stage for fair comparison, in fact I measured both at 197rpm and pump 1 had 917mv of pressure and pump 2 980mv of pressure at the same point all of this confirmed to me pump 1 was the weaker pump so why would the engine not start on the better pump? I swapped back again and this time the engine started which is odd.
There are some tsb's concerning the cam lobes wearing and the followers having damaged rollers which in theory could give the same results so I removed both pumps to check the cam and rollers which were fine and then decided to swap the pumps position just to 100 % confirm one of the pumps are at fault. This is what happened
You can see that the lower contributing pump hump has moved nearer the sync confirming that 1 pump isn't as good as the other but I still didn't know if the better pump was actually good.
At this point I made a big mistake, I thought this is going to be easy lol and rather than mess around ordering pumps and getting authorization to replace them I decided to whip the pumps out of a truck I had in the yard that belonged to me that I use occasionally and had no running issues, I also thought that I could confirm if the better pump was good and make sure it had no other issues before ordering new one/s.
Here is a capture of 1 doner pump and the better pump
So lets put it all back together and send it on its way right... I wish! The active fault had gone but after 8 miles of road testing the fault code returned and back into limp mode it went, I checked it again with the scope and the pulses were still even so what now...
I had checked the leak off of the injectors at some stage with the WPS and I was happy with the pulses and the quantity of the returns over time so I moved on but here is that capture in case I missed something
So at this point feeling a little disheartened with all time I had in it and feeling a little sorry for myself I gave up, I fitted the original pump, I was sure the pump was a problem but not the only one it had and I was getting behind with everything else that needed to be done so I asked the customer to take it away to get a second opinion and I wasn't going to charge for the time spent to that point as I didn't feel comfortable replacing the pumps knowing it would still have an issue and then I'd own the problem, the customer called back and insisted I replaced the pumps anyway and if it didn't cure it then he'd take it to the dealer, so I fitted a pair of new pumps which did make the pressure even like my pump but as expected it didn't fix all the issues so the customer took it to the dealer and they have said it needs 6 injectors and he now wants to bring it back for me to do which would be bad enough but although its possible I don't see it in my leak off captures.
What am I missing?
I know FPT has a procedure and specs on injector return volume which is used when there are specific codes or performance issues.
If the engine fails the returns volume test the next test would be to cap one injector at a time to attempt to determine which injector(s) are causing the excess flow.
I theorize that the injector design allows for fuel to flow out the return easier than the nozzle due to some sort of internal wear.
Not familiar with the D7e design, would the return flow test be an option? Agree that 6 injectors is possible, not likely but possible.
Thanks for the input, yes that test is the exact same as what I do on this system. When I find hi returns volume the capping of the injectors does pinpoint the problem injector pretty accurately and has never failed me on this system in the past. I have seen it where all 6 injectors have failed on this system but in those cases the engines never started because the injectors were completely blocked with debris from pump failure. On this occasion I never got to the point of capping the injectors as I felt the return volume was perfectly fine and added to the test for volume I had the Wps inline measuring for pulses so was quite shocked by the dealers diagnosis.
Hi Sharpy, sorry to hear to about your troubles. This fuel system has driven me to madness before.
It looks like you have gone through it thoroughly. Did you check for filings in the filter housing? This is the first thing I check when I get the dreaded call for one of these. I find taking a fuel sample and putting it in a black aerosol can cap can show the particles clearly. Also the hand primer unit can suck air and give low pressure codes.
I wonder if doing the leak off test with your WPS or looking closely at rail pressure while the regulator is disconnected, which would result in max rail pressure, would show anything more conclusive with regards to injector issues?
Hi Carl, I didn’t look for the filings in the filter as someone had been there before me and replaced it but to be fair I stopped worry about them as when these very first come out the company I worked for at the time had a full fleet of them as skip lorry’s and we used to service them 12 weekly and fairly early on I picked up the filings in the filters and it ended up with many meetings with our company Volvo big wigs and Shell who used to supply our fuel as they were blaming each other and us with various BS and at the death of it after personally mopping and drying and vacuuming the inside of our 35k litre diesel tank (no fun and I’m sure took years off me) as that got blamed to we ended up regarding it as normal as every single one of the trucks was the same with filings present at each 12 week service from new and yes some of them did have fuel issues down the line and my god did I get my share of those which is one of the reasons I tried to swerve it and basically that 1 fault code that Should have translated to “there’s a fault with the fuel system good luck” lol. Back then I didn’t even have a scan tool let alone a scope but used to get by but it was our own fleet the Labour was effectively free and any parts I bought went on the shelf for the next one if it didn’t work or we stole the parts off a good truck till we knew what the problem was, I was never keen on that one as it always always caused issues with the “Hanger Queen” even tho that one ended up with the new parts. I have seen a couple with the pre filter head drawing air and 1 with the drain in the bottom of the main filter leaking the fuel back to the tank but I disregarded those early on as the low pressure seemed good and stable (that may yet have been an error on my part as I’m not sure on the final outcome yet) thanks for your input it all helps
