*Fixin’ the Sub*
Evolution of a Rubicon Suburban
By: Natrex
10 November 2008

My daily driver is a 95 k2500 suburban diesel that I picked up fairly cheap. The prior owner had the tranny rebuilt and a new injection pump installed and he had the receipts to prove it. He was willing to sell it cheap because there was a seemingly endless series of problems with this beast.

Translation = it had lots of things wrong with it including throwing/eating the serpentine belt, service engine soon light, overheating, low voltage, and no power. The belt was an easy fix with a washer as a spacer on the alternator but the rest are all related.

First attack was on the cooling system. Online forums indicated that the factory redesigned the cooling system in 97 so "obviously" that's where I should start. The upgraded water pump and thermostat lowered the average temp from 235 to 210 and lowered my bank balance by ~$350. www.SSDieselSupply.com

I also flushed the system, cleaned out the leaves between the condenser and radiator, and tossed in some Red Line WaterWetter for good measure. By the way, if a vendor mentions something about “minor” grinding may be required, take this as a hint that you will need to spend two days with an air grinder performing exotic yoga positions to make the part fit!

While better, the temperature would still occasionally spike to 235 which was particularly annoying considering required turning off the AC in a Texas summer. Consulting the online gurus once again, I discovered I needed the Duramax fan upgrade which was available for only $189 plus shipping. The part got ordered and installed and the spiking behavior was pretty much eliminated.

The ‘burban was still dog slow and would barely keep up with traffic. Towing was almost impossible because of low power and the extra load would again cause the temperature to climb above 235. Okay, enough with the online open forums, time to get professional help in the form of the factory service manuals. I bought mine from a website www.autorepairmanuals.biz for about $175. The information in these manuals is great and the only drawback is that they are photocopies and the toner was a little light on some pages.

1995 was the last year for OBD I that allows you to get the diagnostic codes with nothing more than a paper clip as a jumper in the diagnostic port. Wow, this computer was storing a lot of trouble codes. The brake light switch, torque converter clutch, inlet air temp sensor, waste gate solenoid valve, and accelerator pedal sensor were just some of the problems.

First thing to fix was the brake light switch which I figured might be related to the torque converter problem. It was a $5 part and took about half an hour of human origami to swap. (Working on cars does wonders for your flexibility) I cleared the codes by disconnecting and reconnecting the batteries before a test drive. The accelerator pedal error and waste gate error came right back.

The accelerator pedal sensor is fairly expensive and has triple redundancy so I decided to live with that one for a while. If a second system in it fails then I’ll replace it but it should be okay for now. That left the waste gate solenoid as the next item. The service manual has a troubleshooting tree but I needed a vacuum gauge to diagnose the problem. That meant another trip to the parts store for a $35 gauge. Yup the solenoid valve was the problem and no there was nowhere local that had a new part. Online it was ~$40 including shipping but would not arrive before the Fall 08 Deep South Campout.

Decision time: Do I try to pull a 26 foot travel trailer with a 98 Land Cruiser or a sick but reliable ¾ ton suburban? Slow and safe won so the suburban was called up for duty. Towing speed was limited to just 55 mph but stopping and handling was no problem. A moment’s inattention towing in the mountains did let the engine temp get to 250 but I immediately pulled over and turned on all the heaters to cool it off. No apparent damage done.

The drive back was painfully slow but uneventful and a new waste gate solenoid was waiting on me when I arrived. It required all of five minutes and no strange contortions to swap. Problem solved! The waste gate was limiting the boost from the turbo and causing too much fuel to be dumped in the motor. The temps never climb above 200, it has good power, and my mileage has gone up 1.5 mpg.

The only other thing I’ve done is remote mounted the diesel injection driver because the online gurus said it was likely to fail. A spare driver was $65 and I built the heat sink myself. Now I not only have the original one as an installed spare which can easily be reconnected but my alternator is putting out more voltage. It seems the original driver was consuming a lot of current and keeping the voltage down around 12.5 instead of 13.8. I was planning on buying a new alternator and two new batteries because winter is coming and diesels need lots of juice to crank on cold mornings.

The moral of this story? Finding the cause of a problem takes more detective work with computer controlled vehicles than in the “good ole days”. I spent nearly $1000 on parts and miscellaneous things but I now have a reliable 4wd vehicle that can haul lots of gear and people. I also have crawled all over this thing and that intimate knowledge should come in handy if anything ever breaks in a remote location.


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