6.2 diesel idle

[86c20]

so i got my new 6.2 in and running but it seems to idle high. all the time. now i have unpluged the fast idle wires still high. backed out the idle screew still high. but pull back on the throttle its self comes down to where i think it should be. no working tack yet. i think i have the return spring in the right spot.

just for numbers and a guess. i would say idle is around 1000 rpm

also she will rev up on her own then come down for a bit then back up. its slow but it is a good 500 rpm jump.

i know my fuel is old and i know it is a mix of wast oil and diesel. close to 50/50.

any help would be great. thanks

[86c20]

one thing i forgot to say was the temp sensor reads 300 all the time now too. it is pegged on hot. not sure why.

[hatzie]

Originally Posted by 86c20

so i got my new 6.2 in and running but it seems to idle high. all the time. now i have unpluged the fast idle wires still high. backed out the idle screew still high. but pull back on the throttle its self comes down to where i think it should be. no working tack yet. i think i have the return spring in the right spot.

just for numbers and a guess. i would say idle is around 1000 rpm

also she will rev up on her own then come down for a bit then back up. its slow but it is a good 500 rpm jump.

i know my fuel is old and i know it is a mix of wast oil and diesel. close to 50/50.

any help would be great. thanks

Surging is usually an air leak into the fuel lines just before the DB2 injection pump. Still have the rectangular Stanadyne 80 fuel filter on the firewall?
The late 1990s top loading GM Stanadyne Fuel Manager (ACDelco-10226035) that sits to the rear of the intake manifold is easier to service and it doesn't leak like a sieve.
Get one of these---> http://www.amazon.com/ACDelco-10226035-Professiona...

Or get a Spin-on CAT or Racor off an old piece of industrial equipment or Medium Duty diesel truck. Be choosey. Look up the element # to see whether it's a commonly available part and whether it's a PITA to service. Some CAT and Racor filters can leak just as bad as the Stanadyne 80 Box filters.

Originally Posted by 86c20

one thing i forgot to say was the temp sensor reads 300 all the time now too. it is pegged on hot. not sure why.

Completely separate from the fueling issue. Pegging the temp gauge is a shorted temp wire... usually means the wire is sitting on the exhaust manifold.

[86c20]

yea i still have the 80 filter on the wall. been on the list to change to something else. i think my boss has a spin on fuel water separator i can have....if i can find it again lol.

i was not sure about the temp being tyed into the fast idle system or not. thats why i was asking. thanks, mike

[barry1982]

Hi there,

Yes, the temp is tied to the fast idle. On my 6.2, the plunger comes out and it "fast idles" when cold. I'm not exactly sure how the system works, because it not only idles faster, somehow the timing gets advanced as well. When I drive on "fast idle", the engine "rattles" until a certain temp is reached. You can tell as soon as it happens, because the engine gets quieter. I recently had a similar problem to yours right after putting in some bad fuel. My truck is an 82, so I have the primary/secondary spin on fuel filters. I ended up draining the fuel tank, flushing the lines, and installing new fuel filters. Filled the truck with good fuel, bled the injectors, and problem went away. Did you try unplugging/ plugging in the wire on your temp sending unit? Sometimes a dirty connection will give you false readings.

[hatzie]

I agree partially... The problem could be his fuel.

There are actually two or three temp sensors on the DB2 equipped 6.2L engines.
The gauge runs from a thermistor type coolant temp sensor with high resistance at low temps and low resistance at high temps. You'll find this sensor in the left cylinder head.

Located at the rear of the right cylinder head is a two terminal normally closed temp switch that opens at 125°F. It controls the HPCA (housing pressure cold advance) solenoid inside the DB2 pump providing 3° cold timing advance and, the high idle solenoid that kicks up the cold idle.

On some 1984 & later trucks there's another two terminal normally closed temperature switch that opens at 125°F to control the Glow Inhibit function of the later controller. It's found near the right front of the intake manifold where the 78-83 multi-pin glowplug controller was located on the 5.7 & early 6.2L engines.

The 1994-2001 DS4 equipped 6.2L & 6.5L used the ECM to control several functions from one thermistor CTS... Temp gauge, Cold advance, Cold idle, and Glow inhibit are controlled by the ECM on these later trucks.

[barry1982]

Thanks for the great info Hatzie..... I have been running 6.2's for over 20 years, and was not quite sure how that cold advance system worked. Often wondered what that "sending unit" at the rear of the right head was for......
If I have any other 6.2 questions, I know who to ask!

[86c20]

right rear i am guessin you mean pass side head???

and that really does clear up alot on how the fast side works to. i never really understood it.

now with bad diesel would it not run like crap and slow like gas? i dont see how that would kick up my rpms??? was thinking about my fuel last night. the fuel is 3 years old or better......

[barry1982]

Yes, there is a small " two prong" sending unit at the back of the passenger side head. Up until today, had no idea what it was for........
I can't explain why, but yes my truck was slightly revving up and down after I put in the bad fuel. Maybe the filter(s) were plugging up.....and clearing.... I'm
not sure. A few years ago, I also discovered how important the return line to the fuel tank is! 6.2's recirculate A LOT of fuel. I changed a rusted out fuel tank, and did not realize I kinked one of the short rubber hoses attached to the fuel gauge sending unit. The thing would start, idle fine for a few seconds, than die. Had me baffled for quite a while. I put a short hose on the return line, and dropped into a gallon bucket. The truck idled fine, and filled the bucket with diesel in about 2 min! Didn't take long to figure out what happened after that.

[hatzie]

Originally Posted by 86c20

right rear i am guessin you mean pass side head???

and that really does clear up alot on how the fast side works to. i never really understood it.

now with bad diesel would it not run like crap and slow like gas? i dont see how that would kick up my rpms??? was thinking about my fuel last night. the fuel is 3 years old or better......

I post on VW & MG forums that have international members with Right Hand Drive cars built to drive on UK, NZ, and Australian highways so I picked up the habit of not calling things passenger and driver side.

Right and Left is the drivers right or left hand while he is seated for driving.

Keeping the international nature of things in mind, we have Australian members too, RH & LH is very clear Passenger and Driver side is not because it depends on whether you're talking about a LHD (North American) or RHD (British) vehicle.

[86c20]

right rear it is then lol. makes sense to me. its just like left rear front inner drive tire at work lol