I own a 96 2500 Suburban with a 6.5. Bought it last fall with 150K on it. It is my 3d GM Diesel, but first with the electronics. I have done a few reliability replacements of things like lift pump, glow plugs & solenoid and all the filters, etc. It went inop on me a few months ago, wouldn't run/run long, I replaced the IP and now all I have hot engine hard start/low power scenarios. There is a lot on info in the other topics on that, and I have moved the PMD out from under the intake an put a heat sink on it. My lift pump never seems to run, when should it run?


My other question is, what themostats do you put in it to run it that cool (170-180 from other discussions) and are there any side effects, i.e. worse mileage or carbon build up? Is there a package of instruments that make sense (aesthetically) to measure turbo pressure, fuel pressure etc.?


My priorities are first reliability, then mileage then power.


Thanks, Charlie

Chech to see if the lift pump connector gets power when you turn the ignition on.
IF not your OPS (oil pressure switch) could be bad.
Wiring a relay takes the liftpump load off the OPS.
HowieE has a diagram on his webpage.

I find it useful for priming the filter. you just jump the common to the liftpump wire.
Edited by: quantum mechanic

I would take the pump back for warranty if you can, they can't hardly argue if you say the magic 'hard start hot' words. A weak or inop lift pump will cause power problems too, try and figure out a solution yourself if at all possible, otherwise pay them to fix it.

As ignition is switched on, the PCM powers the lift pump for a few seconds. If crank revs are not sensed, PCM drops power to the pump.


When crank revs are sensed, PCM again powers the pump to start.


As eng oil pressure builds, the Oil Pressure Switch closes, powering the pump thru a second circuit, bypassing the PCM, which then drops it's power to the pump.


What did you do on timing the new inj pump - Time Set, TDC Offset, and such?


Robertshaw 330-180 thermostats are available to lower coolant temps, but if you do much hiway driving or towing, the 195s wll net you better fuel economy.


Late '96-'97 cooling improvement was a dual t-stat housing, allowing better block circulation, quicker dump to radiator.


''98-99 got a HD water pump, at 130gpm, up from 85gpm - again, better circulation to eliminate internal 'hot spots'.


Some use the '97-98 9-blade steel fan, some like the 21" 11-blade DuraMax plastic fan.


Opening up the exhaust system will lower eng coolant temps by reducing Exhaust Gas Temps.


All the above combine for improved engine heat management.


Check Heath Diesel or Kennedy Diesel, or Banks Diesel - all provide gage sets.


Or, check Isspro directly, as they are the main big-rig and aftermarket supplier.


Autometer also offers several types of Boost, EGT, IAT, Trans and Eng Oil Pressure gagesEdited by: gmctd

my lift pump has never run with the ign. switch just in the on position, only when it cranks and after it starts. when you shut down it runs for about 5 sec. until the oil pressure drops down.


baldwin where you at in VA? homeboyEdited by: lupey6.5

Living in Northern Virginia, City of Fairfax. You?

Correct, Lupey. You have a '94 OBD-I - lift pump runs with starter, then OPS, same in '95.


I was addressing CC's '96 OBD-II, with additional PCM functions, incl pre-start lift pump to compensate for fuel drainback.

gmctd -


You asked what I did about timing the rebuilt IP - I did nothing, just tried to put it in the same position. That is what I used to do on 6.2 and 5.7. What do you recommend?

Have any DTC's occured, Check Engine lite, Service Engine Soon lite, since replacing the inj pump?


The elect inj setup really should be checked with a Tech-II. I suspect the timing is way off, resulting in low power, over-heating, hard starts, and such.


Factory setting should be -0.5deg TDC Offset, about 3.5deg desired timing.


See if the tech willl set it for -1.5deg TDC offset, with 8.5deg desired and actual timing. Gives more "pep" to the old bus.


If you decide on Bill Heath's Max-E-Torq towing reflash, you will be set up to go.


You might also pull the radiator, remove all the debris collected between ac core and radiator, and ext oil\trans coolers, if so equipped. Solves most normal over-heating complaints.


Air flow characteristic in '88-up trucks seems designed to help beautify the environment, by vacuuming up all the leaves, twigs, paper, bugs, etc, within a defined perimiter of the vehicle, and depositing it between those cores.

Thanks, yes I've cleaned part of a tree out of the radiator-condensor gap. I get a 0251 and 0370 codes with a SES when it starts hard when hot and yields low power. The engine does not overheat, just starts hard and gives low power when it has been taken to operating temp and then is off for a while. Charlie

You have gotten some good imput so far. I would like to add Injectors, it is suggested you change injectors at about 100,000 miles I waited until 150,000 and had several that were not working as they should and I saw a nice change. The other is EXHUAST, get a decent exhaust system starting with the down pipe. The factory pipe has a built in 45% restriction, they look like the been run over a couple of time by a bread truck.

Both those codes are for the Optical Sensor, indicating the engine may be running in 'limp', or reduced power, mode.


Could be the connectors from the engine harness to the two inj pump harnesses.


One harness is for the Optical Sensor, one is for the inj pump and FSD\PMD.


Disconnect, inspect, and reseat the connections, checking pins for oxidation, or 'push-thrus', and wires for chafing\fraying.


You might start with the three or four main PCM to engine harness connectors just behind the fuel filter, working up to the inj pump connectors, just as a good p.m. routine .


Solve the DTC's, then take it for Tech-II timing setup.

ccbaldwin


i live in richmond where there are plenty of fart-pipe imports for my truck to feed onhttp://www.dieselplace.com/forum/smileys/Big Smile.gif

ccbaldwin,


I have the exact same vehicle as you and was having some strange problems (also codes 251 & 370) check out this post to the end and use the advise I was given and hopefully you can figure it out http://dieselplace.com/forum/forum_posts.asp?TID=11488&PN=2