Couple questions, Timing Advance and Fuel Trims

Well, since I started checking (due to less than expected fuel economy), and found I am running a -30 to -40 timing advance, WTH? Reports other vehicles timing advance correctly, any IDEAS?

Also, the fuel trims report -15 or so LTFT at an idle, if you are driving it is better, I am assuming it is over fueling at an idle and the O2 is cutting it back (or the O2 is bad). Or maybe there is a low speed miss at idle? Am I correct in this assumption?

Thanks for replying, I have a Davis Carchip that also reports the timing on this motor this way (I replaced it with the Equus because I thought it was toast), as a side note I have checked at least 5 other cars, and they ALL run a Positive timing advance with alot more range of change. The Venture stays pretty consistantly in the -30 to -40 range and will only come above that on like decel.

I thought that a negative fuel trim meant that the PCM was dialing back the fuel due to to much fuel (rich which is what I beleive - tail pipe is kinda sooty, not as bad as when I started) and the fuel mileage even on the highway running slower and long distance is never better than 20 (my 99 got consistently 25, even cleared 30 on 1 tank of gas) It was almost identical to this one, other than it had 2 years less age.

The van doesnt run too bad, you can be on the highway and be giving it gas and it will slowly increase, then all of a sudden grow a pair and take off (trans staying in gear - not that much throttle change) It really isnt too bad considering what size the engine is, what RPM the tach shows, gear it is in, weight of the vehicle, etc.

The Idle does tend to be a little rough, the engine does have a rattle to it at low RPM (Camshaft?) I have put plugs, wires, changed coils and ICM in an effort to effect the rougher Idle, Before I put wires on it I put plugs in the thing and for a day or so you couldnt even tell the engine was running (smoootttthhhhhhhh), but it came back and has never left. Also when I take off from the babysitters (about 8 minutes away) to head back home (engine has warmed up for 8 minutes) I drive up a slower street and with RPM around 1500 in 1st gear and also 2nd the van will surge slightly and continuously untill you change your throttle angle. I have spent many many many trips with the scantool in live data mode, the only things I see odd are the negative fuel trims and the negative timing advance.

As a side note when you get on the highway the fuel trims come fairly normal. (closer to 0) Oh well, I will keep at it and mayby figure this thing out, more input is welcome....... :-)

What is the mpg? How does it run otherwise? My mpg is consistently 20-22 .

Your , right. I am thinking backwards. It is rich. Do we have maf sensors on these vans?
I'm not convinced your timing is abnormal. I'm gonna check my 99 soon and let you know.

Do you have ability to read live misfire or misfire history as well?

I messed up trying to quote myself and deleted most of my original post.

Anyways I like how you described the hunting/surging until throttle is moved. Can you move it either way and trouble goes away? If the pedal is returned to original position does trouble come right back?

Yes, these vans have MAF sensors, cleaned mine with some CRC MASS AIRFLOW SENSOR CLEANER. Didnt help.

You can open the throttle a little and the surging will go away and it will accelerate, if you let off it much it is at idle and it idles good. If while you have been experiencing the issue and you try one of the above, return back to the RPM range it will act up again. I dont think it is a TPS as the live data indicates the correct throttle angle.

I did check my 99 today and it displays 5-50 degrees of advance (not negative) Mostly between 30-40 degrees. I am sure your van isn't retarded any.

Yeah, a positive advance is what you want. I may be getting some major knock retard because of a rattle perhaps (camshaft?), or it is the fact this engine is a transplant (dont know donor van's year or mileage), there was a 00 stamped on the passenger front valve cover (my wifes 06 Malibu Maxx has an 04 stamped there). I am assuming that the donor was a 2000+ vehicle (told the guy I got the engine from I needed 97-99 engine). We did have to swap over to the older style injectors, the brackets on the front of the engine had to be changed also.

I show a different CAMSHAFT on the 2k+ vs the 97, so maybe the reluctor ring on the cam is different? Perhaps it is KS voltage (need to check that next as my scantool will NOT access that.) I do have a Fluke 177 that is pretty decent to T/S with tho.)

Noticed the past couple days my clock on the radio was resetting. I started tinkering, found a bad connection (corroded terminal) at the Fuse box on top of the battery), the end on the battery was a replacement bolt on type and the wire was black, Needless to say I went from a 2-3v drop from battery post to fusebox post to a 0.029 volt drop. A major improvement. Wonder if it will make the darned thing run better? Time will tell.

This didn't always run bad right? Hope not.

My point about the timing not being retarded was that if it really was retarded then the exhaust would be noticeably hot. You would fell it and see it very abnormal. Also as you revved it up and reduced the load the numbers would get lower instead of higher.

I believe the - sign is "just there" like it is on my 95 blazer when I scan it. Which scan tool do you use?

Well, it has run like this AFAIK since I put the motor in (bought it with a bad motor), the timing being retarded would probably run with less combustion of fuel resulting in the higher negative fuel trims that I read (again I assume on that one) and poorer fuel economy. There are times when you are giving it gas on the highway and something will just click after a bit (not literally) and it will take off - it doesnt run too bad as it is.

I have tried revving, I have also messed with starting and restarting the thing. I have managed to get the timing to -12 before, but that was as high as it would go.

I did take some voltage readings the other night, I had around 4.7vdc and 36mv AC, unfortunately I have googled to no avail to see what a standard voltage level is. I have however ran into several threads where a bad or weak KS will cause a retard situation... I have the old motor still at my grandfathers house, perhaps I will swipe the KS off it. I hear the 99+ full size P/U's have issues with bad KS due to water/ mud intrusion to them....

Still getting readings no higher than -10 advance (short happening), tried with KS unhooked no change (no code either), tried unplugging the Cam and Crank sensors and still NG, also no code (didnt run long maybe about a minute.)

Checked fuel pressure for kicks. At Idle 38PSI, crack the throttle open and pretty much the same (maybe 40PSI). Pull the vac line off the FPR and 45PSI is the reading. Suddenly close the throttle from a certian RPM and the pressure bottoms out at 35PSI.

Bump for an old thread. Was this ever fixed?