Engine miss on 3 only under load

Engine miss on 3 only under load

Postby Mage42384 [OP] » July 26th 2016, 12:57pm

I've been digging through the forums the past couple days trying to find any solution to my problem...so I hope I'm not reposting this...

I have a 2003 AWD. Engine starts and runs fine, idles smooth, revs smooth all day out of gear. If I turn on the AC and put it in drive, there are some issues.

From a dead stop without AC running, it has pretty good pick up. With the AC, there's no push. If I'm low in 2nd, like I slowed down for a corner, and hit the gas again, big lull even without the AC, worse with it. Takes ages to get up to highway speeds with the AC on, but it clears up over 70 (so a fairly wide bad band of rpms) If I'm trying to accelerate up a hill I'll get the flashing CEL the whole way and for about another mile down the road.

Eventually, I'll get a P0303. Plug in the scanner, see <10 misfires on all cyl aside from 3, which has been in the 10's of thousands.


So...that's the problems I can think of right now, here are the things I've done:

New cap and rotor (distributor seams solid and not wobbling), new plugs and wires (just redid 3 yesterday in case, plug was fine), new AC compressor (chopped the rear lines to get rid of that leak, but still the larger compressor meant for the rear), new fuel pump and fuel pressure regulator, new upper intake seals (TB, spider and manifold), cleaned MAF, checked air charge sensor, new rear cat and O2 (weld on cat, haven't gotten around to replacing the whole Y), various fluid changes, flushes and such things as that...checked my wires, connections, sensors and readings all around, checked spider plug for scorching if that was arcing, it's clean, injector lines aren't cracked, no leaks there, no vacuum leaks, no intake leaks (propane enrich method)


Next step for me is that sea foam cleaner you use through the intake, replace pcv because, why not, it's $5, and maybe if I'm feeling ambitious, try to do a compression test on that cyl, but after that, I'm really out of ideas =/

Any help or suggestions would be appreciated
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Mage42384
Fueling (3/8 tank)
Fueling (3/8 tank)
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Re: Engine miss on 3 only under load

Postby Mage42384 [OP] » July 26th 2016, 12:59pm

Oh, one more piece of puzzle, it really only acts up when it's over 80ish out. It's 68 this morning, had AC blasting to get on the highway, no troubles
Original Poster [OP]
Mage42384
Fueling (3/8 tank)
Fueling (3/8 tank)
Years of Membership: Mage42384 has been a member for 5 full yearsMage42384 has been a member for 5 full yearsMage42384 has been a member for 5 full yearsMage42384 has been a member for 5 full yearsMage42384 has been a member for 5 full years
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Re: Engine miss on 3 only under load

Postby chevymaher » July 26th 2016, 1:54pm

I had the same thing going on in my vans factory form. Sounds like you have a decent scanner to use. Use the live data and see what the timing is doing. My year retards timing when the compressor is running and it is a real pain. It is supposed to prevent knocking under pressure. But like your having misfires instead. It also pulls gas off in the 30-40 range for whatever reason that only made sense on paper to a designer.

It worked at least till you figure in acceptable wear on all parts involved. It never was the best idea to try to make a engine border line running.

Look at the PCV valve blow through it and see if it is wide open. It should have a big restriction and vibrate. I made a independent restriction for mine because new PCV are just that wide open. Makes them suck oil. And is a vacuum leak. Air without gas is a vacuum leak designed into the system.

Next look at the MAP and MAF sensors. Check them for proper operation. Is the MAP reading correctly through the range. Maf's are a crapshoot there is no real way to test them. Both can cause lean conditions and that is a no power and misfire situation.

Look into finding someone who does Tuning. Or buy a tuner. I know your year isn't a powerhouse but making it run right will help. Factory settings are the pits. Main thing is basically hot rod it a little. Just get the engine making any power it is capable of. Sharp crisp power as opposed to the milk toast settings from factory. So in their dream world on paper, it is smooth as possible and better emissions and mileage.

That is a basic explanation of what is going on in there. But it sounds like a lean condition coupled with a improper air/fuel distribution is the biggest problem. Like I suggested a engine tuner would be the easiest way to locate and alter computer settings to fix it. One of those hand ones with pre settings enter and try it deals.

Ignore what the computer is saying. And go cave man. Pull plugs and just read them. Are they to lean or rich. Do they have detonation. Oil deposits on them. (PCV) or other issues. Beauty of computers are they are just extra work most of the time. Find out what the engine is actually doing. Then see what the computer thinks it is doing. Get them synced. Then you can actually work on the problem now that the computer isn't fighting you as much.
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Re: Engine miss on 3 only under load

Postby Mage42384 [OP] » July 26th 2016, 2:28pm

Thank you for the quick and thorough reply. I did all the plugs back in December when I bought the van (153k on it now, forgot to mention), so only pulled and replaced the plug on 3. Seems I've been a bit lazy these past years and don't remember much on reading the plugs, lol, so, I'm sending a pic. She does feel lean, been saying that for a while about it. Been a couple times when it's acting up real bad that I hit the gas and just hear air getting sucked in while the revs drop, first thought was actually a TPS, but that's reading fine. When I did the regulator, I noticed a bit of a glob of sludge under the PCV, and remember the difference it made back with my 77 Caddy, so wanted to do that, but if the new ones are crap, I'll skip that.

As far as the power of the engine, I had a 99 blazer s15 (the ones that were closer to a Tahoe size) with this engine, and that could move. Same engine and trani, but a little lighter. Been hoping this would get close to the same feel, know it won't be THE same, but it shouldn't be a slug either...any ideas on a comparison in feel between these?

Spark Plug
https://drive.google.com/open?id=0B9066 ... kxzUzkxSnM

As for the values, I'll check them on my break. Have a pretty full function Verus that I think I can program with (companies scanner), just have to figure that part out, lol
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Fueling (3/8 tank)
Fueling (3/8 tank)
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Re: Engine miss on 3 only under load

Postby Mage42384 [OP] » July 26th 2016, 2:30pm

I know the timing went crazy it seemed, lol. Think it read up to 45, but didn't really make a note of it since the mech here said it's normal.

MAP and MAF were reading and responding to changes, no spikes anywhere. Looked like all the sensors were good. Not remembering how to read the O2's either (I'm the parts guy here, I don't work on too much, lol) upstreams jumped, but in pattern, and downstream was level.

Didn't note any values though, not sure what standard operating is on this for most things. Still, will get back to that scanner in a few and write things down this time
Original Poster [OP]
Mage42384
Fueling (3/8 tank)
Fueling (3/8 tank)
Years of Membership: Mage42384 has been a member for 5 full yearsMage42384 has been a member for 5 full yearsMage42384 has been a member for 5 full yearsMage42384 has been a member for 5 full yearsMage42384 has been a member for 5 full years
Posts: 41
Topics: 5
Joined: November 2015
Location: Buffalo, NY
Gender: Male
Alias (AKA):
Van Model Year: 2003
Van Make/Model: Chevrolet Astro


 
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