etaomicron

i have a 97 5.7 1500 it drove great for 3 days and one day coming back from work as soon as i hit the dirt road it started bucking. fast forward 6 days later and ive tried about all i can think of.

its throwing a p0300,

on the scanner the engine idles rough from 780-900 rpm
bank 1 o2 sensor is shoving constant .9v on the scanner with the short term fuel trim at -30 at idle
bank 2 o2 sensor is showing steady .2-.3v on the scanner with the short term fuel trim at +50 at idle

the truck will rev up to 3000, thats as high as ive revved it
the bank 1 o2 starts to level out and change at about 1500 rpms and at that point both short term fuel trims start to head towards 0

the truck does have a noticable missfire to the ear, and if you stand by the exhuast its as if only half the cylinders are running as its a put put put.
well come to find out, i took all 4 plug wires out one at a time on the passenger side bank and left them out, not one of them affected the trucks idle. i did not do this to the other side as i knew that side was working because i unbolted the exhuast flange and the pipe for bank 1 has flow coming out, and the other pipe has very little, this is after the cats. so i thought there might be a blocked cat and drill 2 1/2" holes before the cat on the side that had very little flow, and it made no change.

so far i have put new plugs in
i have swapped the ignition coil and module with new units, i have swapped the crank angle sensor and the distributor, none helped the issue.
i suspsected the fuel system but the system holds 55-60 psi once primed for atleast a minute, and it bounces from 60-63 psi running.
everything i read says as long as the system holds pressure when turned off then the fuel system is good.

ive checked the evap system, ive checked the egr valve and brake booster vacuum. and in my mind a manifold leak would not cause one bank to be rich and one bank to be lean.

Jonathan Ellender

What does your plugs look like, and what plugs wires cap rotor did you use?

also do you have old spider injector style or new upgraded?

I have a miss (P0300 code also) that comes and goes.. I'm chasing.

etaomicron

Ah man, I believe 6 of the plugs I had had a layer of carbon already on the new plugs, 2 had fuel on them.

im not sure of the brand name of the distributor or the wires. I believe the wires are 7mm high temp conductors. Not sure.

its got the spider injectors. If nobody has any ideads, my next step is to check the harness and the poppets. I would moreso believe the pcm is toasted than believing all those injectors acting differently within the blink of an eye

Jonathan Ellender

I'm hoping we both get some help; I posted before on this same forums and the other; to be honest most of the Chevy Forums seem dead for these year models. I dont know why.. Dodge and Ford are very active.

I'm hoping a few of the guys still lurking around can throw some help our way lol..

But this is what I'm thinking at least on mine.. you can search internet and you can find injector issue (Its a recall item) mine had some that were really bad Im surprised fuel still got out they were so bad gunked up which is the problem that occurs.. others are arcing caps; one guy even said he replaced his Dist. and it was the 'plate' that was the issue inside it and it cured his issues.. others was spider injector assy. others was the temp sensor...
Ash build up is most likley burning some oil... check with bran new plug run it a bit then park it once its cooled enough to remove the plug in the locations in question.. remove plug see if its soaked or wet.. either fuel (if fuel then your leaking to much out of your spider) if oil then you most likely have a valve guide leak (Very common on these vortecs; or something else allowing oil in cyl. also to rule it out.. check your oill drain oil out seee if after it sat a while if when emptying the oil do you have antifreeze that comes out or anything.. that could be a sign of blown intake gasket (The lower intake) or head gasket.. (do a comp) test.. if you do have antifreeze in your oil thats not good..

In case you dont have a compression gauge and no antifreeze in oil; You can also check and make sure you dont have antifreeze going into your cycl blown inner head gasket.. remove fuel relay, remove the plug wire off the coil, remove all plugs from engine remove radiator cap... go one cyl at a time with the plug in.. (Just the plug it self) have someone turn over the engine a few times.. if there is a blown gasket on the head and allowing seeping what you will see is big *** bubbles almost explode out of the radiator as the compression stroke will put pressure into the cooling system and burp.. if non of the cyl cause that to happen then your good on that.

I'm at a point it has to be something with timing (Distributor) , TPS or possibly my map sensor since there was so much gunk.. i just dont have the cash on hand to throw more parts at it..

So if i did anything I would get timing checked.. you might be able to find a shop near you some actually do offer free basic checking or you can call and ask them most will only charge like 80-90 bucks or (1 hour min shop rate) to put on their big scanner that can see everything in real time and tell you what is actually going on.

thats what im considering doing but then im out another month waiting if i have to replace any parts.

etaomicron

I've hit a wall with it honestly. I ohmed the injectors and they are all 12-13 ohms. I checked the feed wires to the injectors and found no shorts. I drilled more holes before both cats and that didn't help. Oxygen sensors are still reading the same. Exhaust popping, running rich and lean on different banks. I don't have the equipment to test what the computer is telling the injectors to do. But I know they aren't stuck open because it passes the pressure test. No antifreeze in oil. I can check the radiator for bubbles at some point tomorrow.

I'm in the same boat, no money to put into it. And it irritates me because it ran like a dream and just within the blink of an eye it ran like crap. I know someone with a shop and high dollar diagnostic equipment but they are over an hour away and I deff can't afford to get it towed to far. I may just have to bite the bullet and call some local shops and either trailer it or get it towed. Maybe I should have done that in the first place. I can fix the problem as long as it's not pcm related, I just can't find what the problem is.
my map sensor is reading about 79 KPa usually and the temp sensor seems to be working good from my small scanner. Tps is working right I've checked it too. The MAF usually reads 10-15(I can't remember the units) at idle. The egr is working. And as I said I have changed the dizzy and crank angle sensor. And I was able to get the dizzy in without setting a code.

I get what you mean with these forums being dead. It was the same way trying to get answers with my old s10. And then people tell you to Google or search, and trust me if it was that easy, my problem would already be fixed with how much I've googled.

I've seen a lot of weird stuff on vehicles, stuff like this where the cause might be something you would never think of. Anyway best of luck to you too man

etaomicron

No crankcase pressure, no pressure in the cooling system. Could still be blown between cylinders. Idk.

i haven't had time to pull the spider injectors.

etaomicron

So I just got ahold of a compression gauge. All the cylinders had 200 psi after a 5 second crank. Accept cylinder 6 was 0 psi. Well I pulled the valve cover off and the valve spring on the exhaust valve broke in half. So the valve hangs into the cylinder about a half inch.
I pulled the valve up and spun it, if feels smooth against the valve seat, so I'm going to see if just putting another valve spring on will do the job.

i know the engine is still having fueling issues, which Ive almost certainly pinpointed to the poppers. But atleast now I have time to save up for the updated injector assembly.

Jonathan Ellender

Well let us know how it goes; and what all you do to fix it.. you never know someone having same issue might come along one day and follow suite.. I have my post 159 folks have viewed; there is not 1 single responce. Not even a go search google.

I'm about to go take the truck to have it put on the computer for 90 bucks. I think for sure its the dist. or the timing advance but I'm not sure.. I'm in a delimia myself spend the 80 bucsk replace the dist. then possibly take it to have it checked or just pay the fee first then go drop what ever after.. and hope it was correct diagnostic.

Mine is a random miss , sometimes its smooth as glass then either out of no where or at least when it gets a little warm it has what i call a putter, you can feel it a bit.. if EGR plug is plugged in you really notice it bad; but if not then not so bad*.... low RPM seems to be where it happens if i put my foot into it (or it makes you wanna keep your foot in it , it does not do it near as much if at all) but you can tell there is something 'wrong there still' Has power though.. I can go OT or WOT and it will get up and move.. short of just throwing money at it... that's where im at.. lol

etaomicron

It was the valve spring. Popped a new one in and it's smooth now. It's still getting an occasional miss on cylinder 3, haven't pinpointed why. But it runs good now. At speed it still is running rich, so maybe the cats are going out, I'll have to take it to a shop to get flow tested.

Jonathan Ellender

I can't think of many of these chevies these aged that dont smell like they are running rich TBH..

i still have factory one's on mine as well glad you found your problem and confirmed the fix... awesome for anyone in the future having same issues