Help with fault code 078(7) please

[Markspark]

Hi all i have a Colorado 3.0 D4D auto with 194k miles no most of the time when driving the car it drives fine and does everything as it should but from time to time when i come to a stop the engine management light comes on when i press the accelerator to set off, it then goes into limp mode and i have to stop the engine and restart sometimes once sometimes 2 or 3 times. The management light then goes out and it drives fine again so i ordered techstream from ebay and the fault code that is coming up is 78(7) fuel line malfunction. So now im looking for pointers where to start with this one if anyone can help. The car has new filters diesel, oil and air every year (from Roughtrax

 

[Bob]

Things that spring to mind.. cracked fuel line letting air in? Leak back? Sensors aren't my strong point, but afaik there are none before the filter on the fuel line so I'd imagine it's in the engine bay..

 

[Markspark]

It only seems to do it if i have weight on whilst towing but it has done it once with no trailer on the back

 

[Beau]

Seems it has the issue when calling for more fuel, so would point to not receiving what it needs. Either a blockage or sucking air in the line? Start with the simple stuff first right?

 

[Markspark]

i will have to have a look around at weekend. It's hard to find a fault when the car starts and runs fine

 

[Markspark]

Hi a little update on this and still looking for advice. I can drive the car fine then it goes into limp mode and will not clear until i re-start the engine if i stop and leave it ticking over it cuts out also if i plant my foot on the gas it revs to 1500rpm then cuts out but will re-start and be fine again until next time the light comes on. Please check out the video i have done

 

[Bob]

It seems to be an intermittent fault, which to my mind says electrical as opposed to mechanical.

On the fuel line there's a sensor on the fuel filter, and there's the suction control valves on the pump. Then there's the MAF sensor on the air intake. But as the fault suggested fuel line, I doubt it's the MAF

I've had SCV failure, which gave symptoms of holding at certain revs and refusing to pull beyond that, then surging moments later. It never triggered the EML, and never failed to start and drive. The only time the EML came on for me was when the alternator died

Yours being an Auto, is there a specific throttle position sensor?

 

[Markspark]

im not sure on the throttle sensor the problem with this car its been so bloody good ive never really had to look into fixing it
i did try and carry on driving in limp mode but it just does the same as in the video
I'm lost with this one

 

[Beau]

Sounds like the SCV and your truck is on the higher millage end. Was there any way of specifically testing this valve, like the KZ one with measuring the resistance?

 

[Markspark]

I have bought a pair of scv's from Merlin Diesels but have not had the chance to fit them yet. i will update once fitted

 

[Markspark]

The scv's have now been fitted and have not fixed the problem but i have found out today that the fuel is contaminated with what looks like it could be water. How this has happened i have no idea as i only ever use shell or BP to fill up with fuel.
So i have now drained the tank flushed the fuel lines and re filled with £50 BP ultimate and low and behold the car can now not be driven. I start the car and it will rev freely as long as i want it to but as soon as i select drive or reverse and try and set off BOOM it goes into limp mode again. When i do manage to get the car to drive i have to hold the revs high and snatch it into drive it will then drive ok until i have to slow or stop then yet again limp mode. This problem is now really testing my patience

 

[Bob]

When you say limp mode, is it just the eml on and low revving? I wasn't aware these even had limp mode. I go back to my original instinct of a sensor, throttle position?

 

[Markspark]

Hi yes it does go into limp mode which will only allow you to drive at 10mph or rev to 1500rpm, when in limp mode the engine will cut out after 1.5-2 mins

 

[Markspark]

Ok so a little more on this one i will keep updating this post until i have the car running correctly again to help any other member that comes across similar problem

So this morning i have gone out and the car started fine (as it always did/does) ive then gone out in the car and it drove perfect plenty of power and no issues until the engine got upto its normal running temp then its going into limp mode again and cannot be driven. So as the car drives fine when cold im thinking it could be a sensor somewhere but i have no clue which one it is so any help here would be good

 

[Shayne]

The turbo is digitally managed and someone on here had an electronics failure on it but i can't remember who .

The symptoms might not fit its just a random thought you might like to investigate via google .

 

[Beau]

Still sounds like it's struggling for fuel, especially when it got worst after messing around on the fuel related side. I know those D4D engines can be picky with fuel quality. Are there any filters in the injector pump like the KZ one?

 

[Markspark]

Ok so i now have an update on this issue and what has been changed. Firstly the fuel pump was changed with a known good 2nd hand pump this did not fix the problem still the same 078(7) fault at the time the pump was fitted i had the timing belt kit fitted (it made sense to do it whilst the belt was off).

So then the next item changed was the common injection rail this was replaced again with a known good 2nd hand part, this also did not clear the problem so upon checking the injector values again and number one being different to the other 3 injectors i have now changed injector number 1 again with a known good 2nd hand part. Now what i did find strange was the there are 2 types of injectors fitted to my car injector number 1 & 2 are 2 pin injectors with a conversion harness connected to the 4 pin plug, injectors 3 & 4 are 4 pin injectors which i did find very strange.

Once injector number 1 was changed the car runs a lot better and i can still drive it but i do still have the fault so this weekend im going to replace the other 3 injector and fingers crossed that will fix the problem

i will update once this has been done

 

[Higgy]

Sorry to but in.. But a quick glance on Google..... Code 0787 or possible 0627. Fuel Circuit 'Mal' (suction control valve) Also throws up code P0627.... But you probably already Know this..

 

[Markspark]

Scv's are brand new from merlin diesel

 

[Kevin Murtagh]

Hello Markspark did you ever get to the bottom of this fault?? Have exactly same fault and pulling my hair out trying to solve , I have had extremely bad fuel new scv, pump checked, rail cleaned , tank dropped and gauze cleaned , new fresh good diesel , new fuel filter , mine is 2004 so old 4 pin injectors, I thi I they are my fault but , what fixed yours , any help greatly appreciated, thank you