Hi all,

Only me again.... My truck went for it's first big run after I fitted the FICM from Ed and deleted the cat. The quest was a 750 mile tow of a 14,000lb 5th wheel from central France to Spain... over the Pyrenees. The truck fan superbly all the way up, empty and the same towing on the way back but....

Entering Spain from France there is a little hill in the way, namely the Pyrenees. The first climb is about 25 miles at 5-6% which the truck punched up no problem without even slowing. The cruise control was set at 56mph. After the initial climb, it levels out a little and then comes at you again. it does this several times. However, on one of these ascents, the turbo boost gauge on the dash flickered from it's steady 28psi to 15, then to 0 then back up to 28. The truck slowed a little and seemed to be letting off the throttle and then coming back on. At the same time the boost on the Scangauge never budged from 28 psi. I checked the codes and there was a pending code. It carried on fine and later on a similar big climb, did the same again, threw a DTC and check engine light came on. All the while, apart from on the big climbs the truck ran perfectly.

When it did this the second time, I was monitoring MAP and as load increased, the Map readings went from 15.0 to about 38.5 and then dropped to 2.0, then 5.0 etc as load continued to increase. When the load decreased, Map values returned to 'normal' Could I have a faulty Map sensor?

I had another tow the next day, again with hills but smaller ones. It often hit 28psi on the boost but no problems or codes. Like an idiot, I cleared the code on the first journey but forgot to make a note of it. Map reading behaved the same but no running issues were encountered and no codes were recorded.

Any advice appreciated.

Thanks,

Andy

 

Monitor MAP, BARO and EBP at the same time to correlate what each is doing.

Josh

 

Thanks Josh.

Is that while running? KOEO all are within 0.5 of each other at around 14.6

 

While running. You're observing MAP (which is BARO + Boost) however, the turbo is based off the EBP and BARO. If the BARO sensor acts up, it will throw off the PCM and command the turbo back. Same thing with the EBP sensor.

Watch all 3 and then see which one is acting up.

For the 4th PID on Scangauge, possibly throw in the Vref signal and make sure it is a steady 4.5+ volts.

Josh

 

Thanks Josh, will do.

All I know at the moment is MAP goes up to around 38 and then disappears to not a lot but PSI stayed constant at 28. It may be a couple of days before I can try it and maybe longer before I get another tow to load the truck properly.

Will keep you posted. Thanks again.

 

Hi all.

Ok, while running, Baro remains at 14.5, EBP climbs with load up to around 50.0, MAP climbs to around 38.0 and then drops suddenly to 2.0, 4.5, 6.0 etc. PSI climbs to 28.0. when the throttle is backed of, MAP returns to normal. I'm going to check the MAP tube again... Any ideas?

Thanks

 

I forgot the vref value, will have to programme that in and check again. I also should have said that when MAP values drop suddenly from 38 down to 2, PSI holds solid at 28

 

It's not so much the MAP tube as it is the MAP nipple on the intake manifold. Mine was partially plugged with soot and I cleaned it out using the spray straw from a can of WD40. Just be careful not to drop the straw down into the engine. I reset the KAM using my SCT and the truck became more of a Monster after that.

 

Thanks I shall check it again. The bit I don't understand is why MAP reaches 38 and then drops to around 2 but PSI remains at steady and constant 28. I would have thought PSI is derived from the MAP sensor but evidently there is another factor involved?