Truck runs poorly

[Steelkilt]

my truck seems to be running poorly. drove from DC area to western NC last week. got 14.5 mpg on the highway which seems terrible given what others have said they are getting in the mileage polls here. the truck is down on power and on hard acceleration it has started smoking. it has 167k on it. service engine light came on at one point on this trip but went off. i've changed the oil regularly as well as fuel filter (and replaced a lift pump a couple months ago), but i don't know this truck well at all yet having bought it late last year and not having had any prior experience with diesel.

if there is anything i need to be checking i would appreciate knowing, though i recognize this may be hard to diagnose with so little info. i guess i would appreciate recommendations (either here or by pm) for a good trusted mechanic who knows these trucks somewhere near northern virginia who could make this run. though i am always happy to DIY i just need to understand what to look for and how to do it, and that's not working for me right now.

[DmaxMaverick]

Sounds like your boost has gone missing. Start your troubleshooting with the vacuum system. Inspect all the vacuum lines under the hood. They should be in good shape, with no cracks/breaks or hardened rubber junctions. Verify your vacuum pump is able to provide 20"+ at the pump, and the wastegate vacuum actuator is seeing 15" at engine idle. If vacuum checks out, it's likely the vacuum modulator valve, which is upstream of the wastegate actuator. If you suspect it isn't working, try flushing it with WD40. This is a temporary diagnostic fix, if it works, and indicates the valve is on the way out. If it shows vacuum pump vacuum at the inlet, and no vacuum at the outlet (toward the actuator), it's bad, or has lost PCM communication (probably a connector, somewhere).

As a temporary test procedure, you can wire the wastegate closed. If the drive proves to have returned your power and the smoke is gone, you've verified the turbo and wastegate health. Be sure to remove the wire when the test is finished, as leaving it will prevent the PCM from protecting the engine from excessive pressure/heat damage.

[Steelkilt]

thanks for the info! i put a bungee on what appears to be the lever closing the wastegate and power was restored, with exhaust clean again. i like this truck again.

so now to run the other checks you mentioned. wish i had a diagram and pics to help me figure out where things are. any thing like that available here or elsewhere?

[DmaxMaverick]

You don't really need a diagram, if it worked before, then suddenly it didn't. Check the connections at the components (pump, WG solenoid, WG actuator), and follow the lines from component to component. (continue once the physical inspection passes) Check the vacuum quality at the pump, and at the WG actuator. If they are 20+ and 15, respectively, the problem lies with the WG actuator (It should hold the WG firmly closed at idle). If you have less than 20" at the pump, the pump is bad. If it's less than 15 (or zero) at the WG actuator, but has pump vacuum at the WG solenoid inlet, the problem is the valve, or the harness/connectors associated with it. Just for GP, it doesn't hurt to flush the solenoid valve with WD40. There's more, but hit the easy/common stuff, first.

Keep it simple, and it will be. And, be sure to remove the bungee you installed on the WG, before any heavy foot/load driving.

[Steelkilt]

yes, i removed the bungee first thing, even though it had been so nice having power back.

and yes now i've traced things it all seems pretty obvious.

but just to be sure: i assume the wastegate actuator is what sits above the wastegate. black vacuum line from that goes across motor to solenoid. then orange vacuum line runs from there back across down behind alternator to the vacuum pump.

the lines and connections seem in good shape. i'll run the other tests.

btw access to the pump seems very difficult and limited, even when i went underneath and tried reaching up. what is the easiest way to reach it?

thanks again for this advice. very helpful and instructive.

[DmaxMaverick]

Your inspections sound good, so far. You don't have to disconnect the vacuum line at the pump, yet. You can test it at the other end. If you don't get sufficient vacuum there, then you can go down to the pump. The pump should produce 20"+ at the pump (or the main pump line), ideally 25-27". If it has that, then continue to the other side of the solenoid valve. It should be a near-constant 15" at engine idle (testing at the valve outlet, with the WG line disconnected). If you have a test pump, the WG actuator (the canister attached to the WG linkage, and a vacuum line attached) should hold 20" of vacuum, indefinitely, and with this vacuum applied, the WG should not move by hand.

If you need a good vacuum tester, Kragen and Autozone has one (you may be able to borrow it). They're not cheap, but work very well for this, and other chores (like solo brake flushing/bleeding).

[Steelkilt]

i got hold of a vacuum pump and a tester.

i pulled a vacuum at the solenoid end of the line that goes to the actuator from the solenoid and the actuator works fine.

then i ran the truck and tested the vacuum at the solenoid end of the line running from the pump, and there is no vacuum at all.

so i guess this means it is the line or the pump. i guess i have to get to the pump

[DmaxMaverick]

Yep. Let the engine cool a bit, first. Good luck.

[Steelkilt]

Yep. Let the engine cool a bit, first. Good luck.

thanks! so i'm guessing if i have to replace the vacuum pump i'll need to remove the alternator to get to it?

btw, i learned a lot today. most gratifying and rewarding.

[DmaxMaverick]

The alternator comes out easy enough, and will just get in the way if you leave it. Removal is not required, but it's easier in the end if you pull it. It's also a good time to have a good look at the belt, tensioner and idlers.

[Mark Rinker]

Dmax has been giving you great information and guidance for troubleshooting your problem. I would like to point out a proven, and viable option to troubleshooting and maintaining multiple points of failure with the stock OEM boost control system in the future.

http://www.heathdiesel.com/P/HDP1246/

Anyway - not to interrupt your learning curve under the hood. Personally I switched two 6.5L trucks over to this 'set it and forget it' product, removed the vaccuum pumps altogether, as well as the old brittle lines, wastegate solenoid, etc...

[Steelkilt]

Mark, that's intriguing. Do you run it with the factory computer mapping? If not, which option do you use? it looks like one of their programs provides increased fuel economy which would seem worthwhile.

btw, is it just the two bolts on the alternator that i can see or is there something else holding it in place?

[Robyn]

I run the Heath Turbo master on my truck.

The Heath chip has the programing all worked out so the ECM does not get all worked up over high boost and fuel conditions.

You then become the controls that keep the little creature from melting.:eek:

The computer just allows the IP to dump all the fuel your foot is asking for.

This system is trouble free and works as good as advertised.
The vacuum system sucks, Pun not intended.

GM did the vaccum thing to maintain a very safe boost pressure and really errored far too much on the safe side.

For a daily driver the vacuum system is ok (as long as it works right)

The TM will allow the waste gate to blow open even if only slightly as the drive pressure reaches the set limit.

The operation is very smooth and steady and the turbo spools very fast even off the line when the throttle is mashed hard.

Used without a Chip thats programed to work without Vacuum controls the ECM will set DTC codes and defuel when the boost reaches too high.

This is anoying and will ruin a nice hard run.

Get a TM and a chip and life will be very good indeed.

Robyn

[Mark Rinker]

Mark, that's intriguing. Do you run it with the factory computer mapping? If not, which option do you use? it looks like one of their programs provides increased fuel economy which would seem worthwhile.

btw, is it just the two bolts on the alternator that i can see or is there something else holding it in place?

You can read lots about the turbo-master by searching in this forum on turbomaster, turbo-master, heath, etc...

I ran it with stock OEM programming with no gauges, and with Heath's ECM with boost and egt gauges. If you only tow occassionally, you could get by fine with no gauges. If you tow alot, or heavy, gauges are a good idea to fine tune the boost level.

Not sure I ever saw increased fuel economy - but I had 3500 series trucks with heavy flatbed bodies and didn't do much empty daily driving. The additional power with ECM upgrade and a little more boost is VERY noticable, and makes a 6.5L run about like a stock Duramax...

If it were just a loose vaccuum tube, or even bad solenoid, I'd probably advise you to fix either one, and look into the turbo-master. However, if your vaccuum pump is already out - why replace it? Personally, I'd spend the money on a better mousetrap that aleviates future repairs.

As always, my .04 worth... no disrespect for DMax's approach

[Steelkilt]

well, i'm about sold on the turbomater. best of all it's even a little less money than a new vacuum pump. of course i'm not counting the new computer. may as well put on a shorter belt while i'm in there, and the tensioner pully feels a bit worn. the injectors are probably getting old at 167K so probably should do those as well to keep it running cool and economically and get maximum benefit from the new setup. of course the exhaust should be opened up some and will probably need a set of guages as well so i can keep an eye on everything. thanks for pointing me in the right direction so i could save the $15 and get rid of the vacuum pump!