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I have a 2000 GMC Savana 3500 5.7L V8. From time to time it runs very rough where it shakes the whole van and has no power. Here is what I have done so far: Replaced spark plugs, wires, distributor cap and rotor, replaced all gaskets from the lower intake and up, new fuel filter, different spider injector assembly. Fuel pressure tests out fine. Compression tests out fine.
I had it on my scanner also. Most of my issues are with bank 1 I believe. The short term fuel trim bank 1 will sit at -30.5 forever even though the o2 sensors on that side are reading a lean fuel mixture. Bank 2 everything seems alright.
Could there be a problem with the computer cutting fuel to bank 1 for no reason. Sometimes when I first start it in the morning right away the fuel trim will drop to -30.5. Other times it will run fine for a while and then out of no where just start dropping to -30.5. Any advice would be greatly appreciated!!!!! Thanks!
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do you have any codes or engine light? what is the voltage reading for that bank of cylinders?
http://www.ericthecarguy.com/faq/solving-automotive-performance-issues#PerformanceIssues
No codes or check engine light. The voltages on bank 1 sensor 1 fluctuate between .150 to .300 volts while short term fuel trim is at -30.5. To me the o2 sensor is telling the pcm that is too lean and should be adding fuel, not taking it away.
fuel trims are showing a lean condition, fuel trims are also set too far back too trim, did you try disconnecting the negative battery cable and re setting the PCM? kind of a funny accurance.
That I have done several times 🙂 Once when I started it the fuel trim went to -30.5 without even going into closed loop. I even went as far as to pull the connector off the o2 sensor on bank 1 and plugged it into the o2 sensor on bank 2 which was the good side of the engine and it still dropped to -30.5/
something just isn’t right here… if the 02 sensor is reading lean the PCM should adjust fuel trims into the positive but it is EXTREMELY far into the negatives which is making the lean condition, i am trying too think of what would tell the PCM to do this besides the PCM is going bonkers.
i would NOT recommend replacing the PCM but have a look at the connections for corrosion and if you can smell something burning or something, but don’t replace the PCM just yet it could be something wonkey.
Haha…yeah me and you both. The only sensor that is biased from one side of the engine to the other is the o2 sensors. But the pcm is seeing that is needs more fuel yet is cutting it. It is a unique problem. I will check the connections again tomorrow. I had unplugged the connectors before and checked and they looked nice and clean but who knows. I’m leaning towards that the pcm is not bad as this is not normally what a bad pcm would do.
It still ran like crap. I tested the mass air flow sensor when this started happening months ago. I think I may try cleaning it anyways. One question reason I never really suspected it is because I figured it would effect the overall engine performance and not just one bank of the engine.
I will check it out regardless. I’ve tried just about everything else I think would effect the fuel trim. Although on my scanner the Maf seems to read alright and smooth readings with throttle response. I may just have to break down and take it to the shop. It’s hard to take it there after investing so much time, research and money into the problem haha 🙂
I’ve been going back on my old notes;because I remember something about this issue…I can’t find anything yet…I’ll keep looking…
I guess you had these issues before you started working on your van? I’ve never seen a -30 trim value on a GM before, I think maximum negative Value is-20%. Can you get pause width modulation value for the fuel injectors on your scan tool? If you can, what is the value on the left bank at idle?
Yeah I didn’t think my pcm went to a 30 value either, it just might be my scan tool, not sure. I did have these issues before I started to work on the van. Actually when I bought it 2 years ago it had this issue but it went away. Now it seems to be back to stay. My scan tool does not show pulse width, sorry.
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