Fuel Quality? - Check Engine Light

[damork]

I've started to see a pattern with my truck and fuel quality & the famed check engine light and code 36.

I carefully document all the fuel I buy and always use Stanadyne blue as well. During the winter months I started to notice the truck was not starting as well as usual and I was getting code 36 / check engine light. This was nothing new but I decided to try a little experiement.

A switch to more expensive Amoco Premier diesel cleared it up. When that tank was gone I went back to my usual source and the code came back immediately. I continued to alternate this over about 6 weeks and it was like clockwork - I could reproduce it with a simple change of fuel. Lots of white smoke and sputtering at startup were other symptoms.

I'm staying with the good stuff regardless now, but it is disappointing that diesel fuel quality is not more consistent. I'm considering having a lab test done to see what I really have - but I am not so quick to blame the electronic injection pump as I was in the past.

[DmaxMaverick]

It's more than just fuel quality.

If you are in an area that mixes winter grade fuel, normally it will be a mix of #2 and #1, the ratio depends on the local temps.

Premium (true premium), on the other hand, is usually straight #2 with additives to handle the cold temps.

The difference? #1 has lower viscosity and energy than #2. If you mix the two, the fuel will be thinner, and have less energy.

What you are seeing is probably a pump that is wearing out. The tollerances have opened up, and the thinner fuel is making it harder to build pressure, with less consistency. Couple this with the lower BTU's of the mixed fuel, and you have an engine that doesn't run as well.

Code 36, pulse width error-long. Goes right along with a worn pump on thin fuel. The higher viscosity fuel is probably keeping the performance right on the edge. No telling how long that will last.

[damork]

The point of my post is not to rule out the pump, but to consider fuel. I firmly believe fuel quality has a bigger impact on our GM diesels than most people think. We've had 6.2s and 6.5s in our family and everyone agrees they tend to like top quality fuel. It is real obvious if you get a bad batch. The most obvious is a lot of white smoke instead of a relatively smooth startup when cold.

If I run straight #1, my truck starts right up and levels out quickly with little smoke at temps down to -5F without being plugged in. #1 is thinner, and if my tolerances were bad I would have great difficulty starting at sub zero temps, but that is not the case. I credit some of it to using Stanadyne blue in every tank. The Amoco fuel is a blended low sulfur fuel, but is advertised to have a much higher cetane rating. The economy is not as good due to lower BTUs. More BTU

[TurboDiverArt]

Wow, good write up and good info. I have not had problem like that, knock on wood. I'm not so sure exactly how "clean" my fuel is. I fill up at a large Hess station that is right off the highway; they have a separate diesel dock so big rigs can fill up both side tanks simultaneously. Lots of big rigs fill up there. If I fill up midweek there is always a line where 4 trucks are filling up at the same time. When I change fuel filters every 10K it's dark brown. Don't know if this is typical but I was surprised nonetheless. One of these days I'll take a digital picture of the filter next to a new while one.

On the subject of new fuels. Is there a web site or some way to find out when and where the new "even lower sulfur" fuels are going to be implemented first? My truck being a 1999 has the "Low sulfur fuel only" sticker but having no idea exactly what this means assume that it does not mean the

[Barry Nave]

I buy my fuel also through a high flow truck and car station.
My filter,change @10K always look black.
Never seen a brown filter.

[damork]

My filters are also black, more so after a biocide treatment.

[curmudge1]

When you get the SES & DTC 36, it's cold, right? Does this symptom go away after the truck warms up?

This is the 2nd winter I've had this symptom, and it seems to have gotten worse... lasts longer. But the SES light stops coming on eventually after things get warmed up.

I was recently wondering about this... isn't there a fuel heating element in the fuel filter? Perhaps that has gone bad? How could I tell? And, can the heating element be replaced, or does the whole fuel filter assembly have to be replaced? I bet that part is expen$ive from GM.

[TAG]

I have noticed the same situation with my 95. I have had it for 4 years now and i had the pump replaced 4 months after i bought it. The harder starting & smoke started the day i picked it up from dealer that replaced pump. It took about another year to figure out that it started different depending on where i got my fuel. I buy fuel at 2 different places - one by my shop, one by my home. I have 80,000 miles of experience with this phenomenon. When i fill by home starting is much better with very little smoke, when filling by shop it starts hard in hot or cold weather and the difference is very noticeable. I put guages in 2 months ago and now i am seeing a trend there too. Good starting fuel has 25-50 deg less exhaust temp & 2-3lbs less boost on same 60 mile loop i drive every day. This is very repeatable. i still think there is a flaw in some pumps that makes them fussier about fuel. I have seen other posts that seem to back up my theory. No answers just observations.

[damork]

Yes - the pattern is noticeable when it is cold, and the light goes out after warming up. On mine, the better fuel eliminated the symptoms.

I usually buy fuel from one source if it works well. About 2 months ago I thought I was losing a pump. The truck chugged and wheezed, SES light was on, blowing white smoke and all. I switched fuels and it was like driving a completely different truck. I don't know if they switched refineries or what, but I have never experienced quite that much of a degradation in performance from fuel. This was from an giant oil corporation as well.

I went through the same white smoke/hard starting issue when I owned a 6.2 Jimmy then switched fuels to correct it.