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I have an 02 Gmc Savana 350 4l80 130k. I have no power. I hit the gas and it surges like it wants to run but then just lays over. I have tested and retested every sensor that I can and have found nothing that is out of the specified parameters. Anybody have any ideas as to what I can do from here? :snoopfacepalm:
This is killing me.I don't want to drive it anymore.
 

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48 at idle and 60 when I give it throttle. Doesn't look to drop off at any point in time. Replaced the fuel pump about two years ago along with the spider injectors and transmission. Run Lucas fuel treatment every tank. New AC plugs <5K. It runs better when cold and as soon as it goes to open loop it goes flat. It has never run well. Certainly not the way it should. Feels like it is over carbureted. Surge when you hit the gas and when you let off.
Today when I went to use it, it stalled 4-5 times before I could get it to run. Sometimes it is very hard starting. All of this is VERY intermittent.
 

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That idle spec is a bit scary. Should have another 10 psi on it.

Spec is 60-68 psi at KOEO(Key On Engine Off) then when you start the engine KOEngine Running, the pressure will be lower as the vaccuum will cause teh FPR to lower fuel pressure.


Cold truck starts in Open loop, the once warm starts to read the O2 sensors as its in Closed loop.

Hows it run at WOT? I mean put it too teh boards and hold it for 7 seconds? Better or worse? At WOT the PCM goes to PE mode/open loop and ignores teh O2 sesnors. If it gets a lot better at WOT, I suggest precat O2 sensors.

peace
Hog
 

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Yea, I always get open and closed confused. It is adequate until about half throttle and then lays over. Low rpms it has nothing. Very sluggish downshift. Have to really jam the throttle and then I get a surge and it lays over.
 

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Sorry I corrected above, should be 60-66psi, not 60-86psi.

Your pressure isnt bad, I had a Vortec 350 that had a bad coil that kind of behaved that way. New $30 GM coil fixed it.

The intermitent part is frsutrating. You already did the CSFI tgo MPFI spider change, a new pump COULD go in 2 years, Ive had them go in months, best luck with GM pumps.
Hard starting can sognify a bad pump. Listenfor it as it will run for a few seconds after you stop cranking. If you dont hear it, could be an issue. Ive had pumps reading 60 opsi be fixed by another pump. If pump isnt running, Ive taken a rubber mallet and whacked the tank when someone else cranks the estarter and gotten them to fire. The concussion vibes the brushes of the fuel pump and allows the pump to turn.

But the open /closed loop driveability isnt fuel pumpish.

Any code reading ability? Any engine lights.

The WOT test I described above is best done with tehs elector in 2nd gear. Get above a speed that wont allow your trans to downshift, bury the throttle to the boards if it runs crappy at low throttle and better when you open thethrottle 100%, could be the precat O2 sensors. You must open teh throttle wide open for a few seconds at least as there is a PCM timer that counts 3-4 seconds before the PCM goes from closed loop to PE mode. All of this is done when engine is warmed up.

Wish I could help more.

peace
Hog
 

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Discussion Starter #8
It ran like this before I changed the pump and spider injectors. I don't want to have to change the pump again. It was a real PITA.
No codes stored or active. I have Scan XL and can do real time data logging.
2nd gear is when it is the worst. If I downshift to second at 40ish it really lays over. I have nothing until it gets to about 55 and then picks up a little.
Low rpms are the worst. I have to ease into the throttle. If I just mash it to the floor it just lays over. If I ease into it there is a point at about 3/4 throttle that it picks up.
I have run the TPS test a bunch of times and don't see a dead spot on the DMM and my scan program shows a smooth curve up to 4.5 volts.

More help than you think. Sometimes you just have to talk it out with someone. I didn't know about PE mode. What does PE stand for?

Thanks
 

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It ran like this before I changed the pump and spider injectors. I don't want to have to change the pump again. It was a real PITA.
No codes stored or active. I have Scan XL and can do real time data logging.
2nd gear is when it is the worst. If I downshift to second at 40ish it really lays over. I have nothing until it gets to about 55 and then picks up a little.
Low rpms are the worst. I have to ease into the throttle. If I just mash it to the floor it just lays over. If I ease into it there is a point at about 3/4 throttle that it picks up.
I have run the TPS test a bunch of times and don't see a dead spot on the DMM and my scan program shows a smooth curve up to 4.5 volts.

More help than you think. Sometimes you just have to talk it out with someone. I didn't know about PE mode. What does PE stand for?

Thanks
Sorry PE mode, stands for Power Enrichment mode. AT low throttle engine warm, you are in closed loop reading teh O2 sensors, open loop running 100% NOT using O2 sensors. When hat and you nail teh throttle, the engine needs more fuel so a PE Mode table is read and O2 sensors are ignored. For that short time the engien is in Open Loop/PE mode, or replying on MAF PCM table input for WOT fueling. You dont have to be at WOT, there are a bunch of qualifiers that need to be met before PE mode is entered, such as TPS%, temp, rpm etc and time.

Now, the 2001-2002 Vans with Vortec 350 have the more advanced 512kb dual 80 pin connectors PCM with the last 4 digity sbeing 0411. This PCM was used with your GEN 1E Vortec 350, but also in some Vettes, Camaros, trucks. This is special because the Vortec 350 uses a 4x reluctor(or every tim ethe crank spins 1 revolution, the Crank Position Sensor0CKP sensor is triggered 4 times. Now in the GEN 3 engines they use a 24x reluctor so 24 pulses per crank rev. This is important for those who want to do a 4x to 24x conversion on the Vortec 350 which can allow the newer 8 coil Coil Near Plug ignition, instead of the Vortec 350's single coil/distributer setup.

Big clue that the issue was there before your did the spider upgrade and fuel pump swap.
Sometime when its dark, start the truck, shut off the headlihghts and look around teh plug wires and distributercoil ofr arcing. I could actually hear the coil snapping when it was failing, new coil all better. I suppose you would have to pull the doghouse to check out the coil/distributer.

FYI If you think you are flooded, hold down the throttle wide open and then crank. So long as the TPS is WOT the injectors wont fire thus clearing the combustion chambers.

Also check the under hood fuse box for a blown ENG B fuse.

I just had a thought, this all could be an upper intake leak as well. I did some work and the seal around teh throttlebody pinched and it wouldnt run right.
So much stuff I have had with tehse L31's.

The intermittent part is a bitch though.

peace
Hog
 

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Discussion Starter #10
The intermittent part sucks bad. I don't think that my scanner is quick enough to catch the millisecond glitch.
I did think about a vacuum leak so I sprayed the whole intake area with carb cleaner and had no change.
I will have to wait until tonight to run it in the dark and see if there is any arcing going on.

Thank you for your time.
 

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That was the first thing that I thought of, because it is intermittent, I thought that the times that it runs adequately, never well, was when the MAF had gone through a self cleaning cycle. I took it out and hosed it down with MAF cleaner and then tested it. Got good results on the test but no change in driveability. ?????
 

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Just started it up and didn't see any arching but my distributor is squeeking. I put a little pressure on the cap and it goes away. :banghead:
 

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I do a cap and rotor every year. Be sure that the distributer that you screw the cap scvrews down into arent broken. The loctite on new screws will strrip and break the hold down. Use the old screws from previous distributer cap, or remove the loctite stuff.

peace
Hog
 

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Boy is there a lot of crud in the cap. Rust in the rotor. I'm sure that affects the pickup. Why would it be vented? That makes no sense. I've had the rotor screws loosen on me before so I am a little hesitant to not use loctite.
Retested, again, all the sensors and I think that it is the MAF. I'll pickup a delco and see what happens. This intermittent thing makes it hard to be sure that I am not just throwing money at hoping something will stick.
 

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Boy is there a lot of crud in the cap. Rust in the rotor. I'm sure that affects the pickup. Why would it be vented? That makes no sense. I've had the rotor screws loosen on me before so I am a little hesitant to not use loctite.
Retested, again, all the sensors and I think that it is the MAF. I'll pickup a delco and see what happens. This intermittent thing makes it hard to be sure that I am not just throwing money at hoping something will stick.
Distributer caps are vented to let out the gasses which are produced by the rotor and cap contacting that transmitting the spark energy.

The Vortec engines use a coil that has a pretty high voltage. Its teh same coil as used in the LT1/T4 engine.

So far as that red or blue locktite that comes already on the threads, I was referring to the bolts that hold the cap on the distributer body, not the screws that hold the rotor onto the metal 1x camshaft sensor wheel.

MAFs can be expensive. I would unplug the MAF sensor connector and see if it runs better. The Service Engine Soon(SES) light should illuminate after diconnecting the MAF connector.
If it does run better that could be indicative of a failing MAF. Unplugging the MAF forces the engine to run in Open Loop following the "failed MAF" tables. You'd think that a bad MAF would throw a code.

I change my cap/rotor every year and every time I can feel the power increase.
These Vortec 305/350's seem to eat caps and rotors quickly. This one of the reasons why GM went with Coil Near Plug ignition in the GEN 3 engines.
These caps often go bad as the tracings that run through the crab cap can arc and crossfire.

This video shows a lot. See the tracing that travels all the way through teh crab cap, from the plug wire to the cap/rotor contact points

I'd try a new cap and rotor before a MAF.

I was also thinking that since the PCM command up to around 34º of timing advance. Because the timing is so advanced any ignition issue is magnified during cruise/light throttle periods

The EGR moror can caus eissues as well, its the round black canister looking thing that at the very front of your intake. You can unplug this as well to see if the EGR is causing issues. The SES ight should come on when the EGR connector is disconnected.

The lack of codes or pending codes could aso indicate a fuel system/pressure issue as there are no electronics monitoring the fuel system.

peace
Hog
 

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Here is a good vdeo that shows the distributer vent holes and explains their purpose as well as other tips.
https://www.youtube.com/watch?v=cpWjF1NRfk8

Also if your fuel trims are running very positive, then your PCM is trying to add fuel to richen up the mixture. Could be indicative of low fuel pressure causing the elan condition.

peace
Hog
 

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Discussion Starter #18
Weather here has been real lousy. Wet and cold. Really haven't felt like working on the van in the wet.
Cap and rotor are still in good shape. I changed then in the fall and I don't see any fouling.
I unplugged the MAF after it had warmed up and drove it for about 15 min. Didn't throw a code and didn't notice any change in drivability. Left it unplugged and when I started it up cold it threw a code. Took it for a half an hour ride. Really didn't run any different. A little studder off idle and as soon as I touch the throttle. The shift is a little more positive and the gas pedal isn't as soft. Again it feels like it wants to run but falls on its face.I will check to see what my fuel trims are today.
I have tested the EGR with my DMM and didn't see any spike or dropoff in voltage. I removed it and there isn't any build up of carbon. I will unplug it and drive it today.
I have been hoping that I sets a code so I have some starting point.

Thanks for your guidance.
 

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Discussion Starter #19
So here is what my stft looks like:

min bank 1 -10.9% bank 2 -9.4%
avg bank 1 2.3% bank 2 2.3%
max bank 1 3.1% bank 2 8.6%

From what I have read these seem to be within acceptable levels. Although the -10.9 is out of single digit range I think that was just a quick glitch. I didn't see it for long.
 
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