2000 5.7 G Box Van ^8600 GVW Fuel Trims

ktmlew · September 14, 2015

I've always figured anything above 7-8 percent was something to be concerned about on other vehicle makes. What is the number you guys would use on one of these? Truck runs OK but seems a bit flat to me from 2300-3000k at 35-45% load.

What is the number that kicks a lean/rich code? This one is running +7 to +11,<135-140> at the above throttle/load. Graphed o2's with Tech 2 and nice sine wave, Truck has 237K miles. Just replaced cats and complete tune-up. Has a screw on fuel filter like a diesel. Fuel pressure on my junk gauge was 55psi but it always seems to read 5-7 lbs low. On the too replace list. Do these respond well to cleaning the MAF? What about injector flushing?

I'm being really picky as i want to build a database so i can possibly head off any breakdowns.

Fredsvt · September 15, 2015

25% for a certain period of time is usually when they kick codes, I've seen some, have 17% to 20% LT and depending on what the ST does, it'll code.

On that motor, how does the plastic snorkel fit on the intake? If the plastic is warped/distorted, the oring inside doesn't seal well, and you have a large after MAF air leak. Also carefully check where the spider's connector is, I've seen some with the oring torn or rolled.

These motors also have intake gasket problems that are quite prevalent, coolant many times, but the upper intake gasket can leak quite badly as well as the lower where it meets the valley. How's oil consumption on it?

Does this have the original spider with poppets or the update with solenoid injectors?

58 psi is dead minimum with poppets, otherwise it won't start with anything lower.

If you go in it, replace the internal fuel pressure regulator before it leaks.

ktmlew · September 15, 2015

25% for a certain period of time is usually when they kick codes, I've seen some, have 17% to 20% LT and depending on what the ST does, it'll code.

On that motor, how does the plastic snorkel fit on the intake? If the plastic is warped/distorted, the oring inside doesn't seal well, and you have a large after MAF air leak. Also carefully check where the spider's connector is, I've seen some with the oring torn or rolled.

These motors also have intake gasket problems that are quite prevalent, coolant many times, but the upper intake gasket can leak quite badly as well as the lower where it meets the valley. How's oil consumption on it?

Does this have the original spider with poppets or the update with solenoid injectors?

58 psi is dead minimum with poppets, otherwise it won't start with anything lower.

If you go in it, replace the internal fuel pressure regulator before it leaks.

Thanks. My technical info is Alldata DIY which costs me $16.95 for each additional vehicle. I have 2009 & 2011 G Van so far. Need to pony up for the 00 G van. Found the data charts for the 09. It indicates LTFT +/- 10 % as "normal". I was suspecting intake vac leaks. Haven't had this one open yet to see if the injector has been updated. Need to get a new fuel pressure gauge and a smoke machine. I rarely get access to these trucks for more than an hour at a time. Heat shields were missing from RH exhaust manifold so it ate the plug wires. That melted the converters down. Scrounged the shield off a junker.

Opinions on injector flushing & top engine cleaners? I'm not a big fan of mechanic in a can.

sneakypete · September 15, 2015

fuel trim dtc's will set for this vintage at -14% and +20%. the condition your describing sounds like a skewed maf sensor. these will respond well from cleaning. take them apart and clean away

ktmlew · September 15, 2015

fuel trim dtc's will set for this vintage at -14% and +20%. the condition your describing sounds like a skewed maf sensor. these will respond well from cleaning. take them apart and clean away

When you say "take them apart" you mean just remove MAF from intake hose and spray it from engine side, right? Cleaned it that way this morning. Didn't get to drive it until this evening. No joy. Seeing LTFT of 12-14% under load when warm, LTFT 4-7 during warm up. That indicates a lack of fuel to me more than a vaccum leak issue. Vaccum leaks should elevate STFT and correct at higher RPM. I'm inclined to believe it's an injector issue. It runs fine until up to temp, about 10 minutes from start up. Stopped at a stop sign and it idled ragged. When i pulled away it missed and stumbled like it was running on 6 cyls for about two truck lengths then took off. Really hard to duplicate, plus driving and trying to watch data is tough. Guess i need to do a recording and see if anything stand out. Really wasn't expecting it to "misfire".

8WA Sman · September 15, 2015

I have no problem with fuel system cleaner but I prefer to use it when the testing leads me there or as a maintenance item. I would watch the MAF g/s when its messing up and see if it's dropping out. If it is I would unplug it and see how the vehicle runs.

ktmlew · September 15, 2015

I have no problem with fuel system cleaner but I prefer to use it when the testing leads me there or as a maintenance item. I would watch the MAF g/s when its messing up and see if it's dropping out. If it is I would unplug it and see how the vehicle runs.

Will have to record it. The stumble is pretty intermittent but LTFT is consistently elevated above 1500RPM. I might try the MAF off my truck as a test part. Can't get my piece of crap Hantek scope to work. It shuts the usb port down. Junk but it was cheap. $100.00 wasted. Would like to get a Pico but not in the budget till after first of year. I guess i can use the PLOT function of the Tech 2 though? Hmmmm?

ktmlew · September 15, 2015

I have no problem with fuel system cleaner but I prefer to use it when the testing leads me there or as a maintenance item. I would watch the MAF g/s when its messing up and see if it's dropping out. If it is I would unplug it and see how the vehicle runs.

Will have to record it. The stumble is pretty intermittent but LTFT is consistently elevated above 1500RPM. I might try the MAF off my truck as a test part. Can't get my piece of crap Hantek scope to work. It shuts the usb port down. Junk but it was cheap. $100.00 wasted. Would like to get a Pico but not in the budget till after first of year. I guess i can use the PLOT function of the Tech 2 though? Hmmmm?

Meant to try it unplugged but forgot. The stumble is very intermittent but I suspect if i get the LTFT down the stumble will be fixed. Feels like a lean stumble. Need scope damn it.

sneakypete · September 16, 2015

honestly I don't find those trims to be a problem on that vintage. as far as the maf, is that the square body style? there should be 4 torx bolts. take them out and split the body into 3 pieces. the center is your heated resistors. clean well. then reassemble.

gm uses maf with map as well so you can uplug your maf and it defaults to speed density. can help with diagnosing as long as you realize your limitations.

how is your tps sensor. staying steady and not dropping out? and don't forget to make sure that fuel filter isn't plugged....

ktmlew · September 16, 2015

I AM just trying to fix the stumble. It DOES act like a skewed MAF. Haven't seen any data that looks out-of-range other than the Fuel Trims.

They replaced the stock fuel filter with a spin on mount. New filter. I will open & clean the sensor the MAF tomorrow.

Will record some data tomorrow if I get to keep the truck.

It does seem to get worse the longer it runs, Heat related to an extent.

8WA Sman · September 16, 2015

Also watch the RPM pid, may have a ignition module flipping out.

ktmlew · September 16, 2015

Also watch the RPM pid, may have a ignition module flipping out.

Had too many other fires to put out today. Driver said truck ran first half of day just fine. Then on return trip acted up a couple times once at higher temperature. Says it's just trying to get past about 20 MPH that is does it. It stumbles and pops through the intake then goes. I unplugged the MAF, showed him what I had done and shipped him. Didn't hear from him this afternoon. Will see what he says tomorrow morning. I have 90+ trucks/vans to deal with so gets pretty busy at times.

ktmlew · September 18, 2015

25% for a certain period of time is usually when they kick codes, I've seen some, have 17% to 20% LT and depending on what the ST does, it'll code.

On that motor, how does the plastic snorkel fit on the intake? If the plastic is warped/distorted, the oring inside doesn't seal well, and you have a large after MAF air leak. Also carefully check where the spider's connector is, I've seen some with the oring torn or rolled.

These motors also have intake gasket problems that are quite prevalent, coolant many times, but the upper intake gasket can leak quite badly as well as the lower where it meets the valley. How's oil consumption on it?

Does this have the original spider with poppets or the update with solenoid injectors?

58 psi is dead minimum with poppets, otherwise it won't start with anything lower.

If you go in it, replace the internal fuel pressure regulator before it leaks.

OK. Intake snorkle is junk. Clips on front are bent, so it flops around. Amazing how much dirty sludge was inside it. Yuck.

One of the clamps on the intake hose was messed up so wasn't really tight.

RH valve cover grommets both junk. Grommet for oil filler tube is missing lower half...it was just sitting on the cover. All after MAF air leaks. You can't tell about some of this stuff until you start disassembling shit...to-be-continued.

Had noticed a strong fuel odor. Re-checked fuel pressure. 62PSI at KO and drops like a rock when pump stops. Oh crap...i know what it is...fuel pressure regulator leaking or a dribbling injector. Some disassembly required. More to follow. Ordered some parts to seal the intake & crankcase ventilation.

Apparently the internal fuel leak was being partly offset by the after MAF air leaks? I had disconnected the MAF electrical connector and driver said it made no difference.

Both times I worked on it previously, the two pilots were standing there waiting on me...I hate that. One was actually sitting in the passenger seat while i put the plug wires on. i finally ended that deal. Told supervisor they had to go. Turns out the freshly installed water pump, I didn't do IT, is leaking at the block to pump gaskets. Red silicone on paper gaskets tend to jack the material apart. I don't use any sealer on paper gaskets. Just two long studs to hang gasket & pump. put other bolts in and git-er-done.

So I believe Fred pretty much nailed this one right out of the box! Will know for sure fairly early Monday.

ktmlew · September 26, 2015

New injector spider assembly fixed fuel pressure dropping off when hot and eliminated fuel stink in vehicle. Tried to get it to leak before changing it but i had to be blazing hot. New TB adapter 'hat' and cleaned MAF, along with replaced porous vacuum hose to heater check valve.

Last test drive LTFT was +6 & +3 with Trim cell @ 6. Much better. Will see what the driver has to say Monday.