Rough idle after 411 swap

[Tparkhill]

update: 165-175psi compression on all cylinders and vacuum gauge showed steady. #8 plug was black and smelled badly of fuel, all other plugs looked normal. I'm at a loss, I'm honestly not sure what to do next.......

[Hutchinson]

Hmmmm,....compression check indicates rings and valves should be ok/sealing,..and you've installed a new MPFI spider thus, it's not a stuck open old poppet style injector (which was common),..thus, a black/heavy fuel smelling #8 plug would indicate no spark to that cylinder.
That's simple to check,...pull the #8 plug, put the wire back on the plug, pull all the other plug wires off and hang them away from any metal grounding source (where they could spark to ground),...then ground the #8 plug to the engine block, roll the engine over with key/starter and look for #8 plug to spark (might as well do this to all the plugs/cylinders while your there,...to eliminate any spark question to any cylinder).
I know you probably already know how to do this,....and probably already know to hold the plug wire with something that insulates you from it. That spark voltage will make you dance a little,...followed by a few choice cuss words,...

One other check is your plug wires themselves,....take an ohm meter (set on ohms) and test each wire,...you should have low resistance on each one,...if they are stock wires, they'll be higher resistance than aftermarket low ohm wires. Google plug wire resistance check to get ohm reading guidelines to fit your application. Either way, if you have a bad wire, it'll read much higher than the rest (or won't read anything at all - means it's broken inside)

Have you received your new Summit distributor and LexTech 0411 yet? May want to consider laying the truck up till you get those two items installed,.....simply as precaution. Also, when you go to stab your new distributor, go to gmtruckcentral.com forum and look for a "how to" from a guy named Aloicious,....he shows you (with pictures/write up) how to set the engine up first, then how to set the distributor up internally before stabbing,...then how to stab it. Everyone swears that when they do it his way (per his write up), it's set perfectly,.....then simply do the +/-2 degree distributor fine adjustment like you did before. Some people say, if you do it they way Aloicious does it, you won't even need to do the +/-2 degree thing,....but I don't know,...I still had to adjust mine a hair.

Lastly, did you check your IAC? If so, whadja find?

[Tparkhill]

Hmmmm,....compression check indicates rings and valves should be ok/sealing,..and you've installed a new MPFI spider thus, it's not a stuck open old poppet style injector (which was common),..thus, a black/heavy fuel smelling #8 plug would indicate no spark to that cylinder.
That's simple to check,...pull the #8 plug, put the wire back on the plug, pull all the other plug wires off and hang them away from any metal grounding source (where they could spark to ground),...then ground the #8 plug to the engine block, roll the engine over with key/starter and look for #8 plug to spark (might as well do this to all the plugs/cylinders while your there,...to eliminate any spark question to any cylinder).
I know you probably already know how to do this,....and probably already know to hold the plug wire with something that insulates you from it. That spark voltage will make you dance a little,...followed by a few choice cuss words,...

One other check is your plug wires themselves,....take an ohm meter (set on ohms) and test each wire,...you should have low resistance on each one,...if they are stock wires, they'll be higher resistance than aftermarket low ohm wires. Google plug wire resistance check to get ohm reading guidelines to fit your application. Either way, if you have a bad wire, it'll read much higher than the rest (or won't read anything at all - means it's broken inside)

Have you received your new Summit distributor and LexTech 0411 yet? May want to consider laying the truck up till you get those two items installed,.....simply as precaution. Also, when you go to stab your new distributor, go to gmtruckcentral.com forum and look for a "how to" from a guy named Aloicious,....he shows you (with pictures/write up) how to set the engine up first, then how to set the distributor up internally before stabbing,...then how to stab it. Everyone swears that when they do it his way (per his write up), it's set perfectly,.....then simply do the +/-2 degree distributor fine adjustment like you did before. Some people say, if you do it they way Aloicious does it, you won't even need to do the +/-2 degree thing,....but I don't know,...I still had to adjust mine a hair.

Lastly, did you check your IAC? If so, whadja find?

You're freaking awesome dood! just sayin....

Ill check for spark later this evening. The burb is running so bad it wont hardly move under its own power so its been parked since this happened. (In the mean time im driving my mildly modded GP GTP with a lot of fun go fast stuff)

I haven't checked the IAC.. .and honestly I'm not sure what to look for on it! help?

And you don't think my new MPFI unit could be faulty? I'm planning to check fuel pressure again to see if the regulator went bad, supposedly if the regulator goes bad it squirts fuel into the #8 hole and causes chaos such as mine....

[Hutchinson]

Having my first cup of coffee this morning, sitting on back porch,....a hair hung-over. But, here we go,....

On the IAC, I've never messed with one,...don't know much about it. I put a new one on my new crate engine when I swapped it,,...never had a problem with idle on old or new engine, thus never had to dive into it. They're cheap and easy to replace. Go on google and read up what it should be doing on Scanner/how to test it,.....then come back and teach me,.......if you do change it, I'd go with the ACDelco brand,.....your less likely to have issues with stock ACDelco replacement parts.

Yes sir, I'd do the fuel rail leak down test to check if your regulator is leaking. Your brand new MPFI spider could be faulty,....doubtful, but could be. Did you use the Delphi spider or was it a cheaper one (I don't know if they even sell a cheaper aftermarket brand for this spider). Usually, when the regulator starts squirting out the round sides/seal, you'll see it on the plugs of both #6 and #8 cylinders. Look at pictures of how the lower intake manifold is ribbed on the bottom and you'll see what I mean. Plus, you'd see bank 2 with really high negative STFT/LTFT's (where PCM is trying to pull a lot of fuel back - because the regulator is dumping fuel in the intake). Bank 2 negative fuel trims would be a deal higher than Bank 1 on a smaller leak,...on a large squirting leak, both sides would be massively negative.

If you do find a leak down during fuel rail test, and have to tear into it,....I usually go a step further to see exactly what's going on,....
Once you remove all the stuff off the top of engine/pop the upper intake plenum off (the plastic one), you'll have to reconnect that pain in the ass metal fuel lines connection back up (careful not to cross thread those two pain in the ass fittings) - if the pressure regulator has been leaking, you could see the carbon buildup on lower intake (right below regulator) washed away. If not washed away, you're soot will be uniform across that lower valley. Next, I pull all the injectors out of their sockets and let them lay inside the intake (take care not to get any of the carbon build-up soot on the injector tips - be careful when you lay them inside/putting them back in their ports).
Then pull the main spark plug wire feeding the distributor (from the coil, as precaution) - first simply have someone turn the key on/engine off, fuel pump should run for a couple seconds and then shut off (charging fuel system to ~58psi),....while you watch the regulator for squirting and/or looking to see if one of your injectors are stuck open (none of your injectors should squirt anything with key on/engine off),....and you can see if any of your individual injector supply tube connections are leaking at main square body or down at the injectors,....just another check I did when I installed my spider.

If you don't find a leak in the spider/regulator, yet your pressure check says you've got a pressure leak down somewhere, then check both your supply and return fuel lines from intake back to tank,....especially, that pain in the ass metal fuel lines connection. If no leaks are found in the lines while pressurized (you'll see darker staining if a leak's in the line),...then, it could be the fuel pump leaking down inside the tank.

I went through all this when I rebuilt my truck,.......

It's hard to desk diagnose what's exactly going on here,...without working on the vehicle personally. You're in a process-of-elimination battle,....or, maybe it's time to take it to a mechanic and have him diagnose. First though,... I'd do a leak down test (verifying regulator/fuel system integrity), then install the new distributor per gmtruckcentral procedure, then LexTech's 0411,...and maybe the IAC for shits and giggles. See how it acts after these things, before taking it to the shop.

Good luck, looks like you've got a little research/troubleshooting to play with.

[Tparkhill]

Hutch, the weird thing is I can smell raw fuel but the fuel trims look completely normal, that's why I think my PCM is bad...

And as far as sending it to a shop. I'm afraid that if I do the first thing they'll say is "why'd you change out the computer? that's obviously your problem" and get ZERO help.

And I know its hard to diagnose over the web but its nice to get other ideas and make sure I check every possibility.

DO you have plans for the holiday weekend? 3 day weekend for you or no?

[Tparkhill]

heres a log showing the idle.... guess it finally decided to cooperate...

Bank 2 Lean.hpl

[Tparkhill]

Heres a video of my spark test light on cylinder 8. not really sure what to make of this.

https://youtu.be/yfJSFCtYvoQ

[Hutchinson]

I haven't looked at your idle scan yet,...I'm on my IPad this morning, on back porch drinking coffee as usual,...but, not hungover this time.

I tried clicking on the spark test light video link and it sends me to my own personal videos? I tried it three times and it did the same each time. Maybe try reposting it.

Where are you smelling raw fuel? At the ass end exhaust pipe or up in engine bay?

I hear you on the shop/PCM thing,....

My plans for this weekend are watching the Florida Gator football game/NASCAR race with my Pop/two brothers/family and having a few carbonated malt beverages.

[Tparkhill]

Hutch I edited the post, hope that helps. the spark plug light is only dim on bank 2 on every single cylinder (2,4,6,8) and its bright as hell on bank 1. and the fuel smell is definitely from the engine. If I take the intake off and crack the throttle it smells so much worse (from inside the plenum) I'm totally at a loss. I seriously think this PCM is trash. I emailed Lextech and haven't heard from him. I'm sure hes busy or something, but I cant wait anymore. Unfortunately I'm going to go back to the black box until I can get a PCM from a trusted tuner.

I tested the fuel pressure again and it holds at 50PSI while running and 60PSI KOEO and doesn't drop when I shut it down.

I also took my infrared temp gun to each cylinder via the exhaust manifolds and noticed that #2 is a completely dead hole as in I can touch the manifold there and doesn't burn the F outta my hand. I put the spark light there and its VERY dim. I'm just totally blown away by this whole ordeal. why would spark be fine on bank 1 and be almost entirely absent on bank 2? bank 2 is still showing -20% fuel trims long term and the short term isn't even trying to correct the long trim... something is up and I'm starting to get frustrated. I need this rig up and going

[Hutchinson]

Yes sir, I see what you mean on the YouTube video.

The first scan log you posted awhile back shows your ST/LTFT's near perfect,...now it's pulling -20,....yet, the fuel pressure test shows your spider/regulator are not leaking,.....weak/intermittent spark on all bank 2 cylinders, but hot on all bank 1. Yet, you have new wires, plugs, cap, rotor,.....

I agree, I'd put the black box back in and see how she acts,....it'll only take a couple hours and you'll halfsplit the issue/know for sure if it's a PCM/OS issue or a distributor/engine issue. May be the quickest way to help you diagnose/move forward.

Let us know how she acts once you swap back to the black box. LexTech is probably doing the family thing this weekend,...

[Tparkhill]

Okay fellas heres the deal. Black box is in and it runs exactly the same, except now I'm actually getting it to show misfires and now at idle it flashes the SES light and I pull a P0300. Which is no help at all because essentially its a "Help I'm misfiring and I don't know why" code. Fuel trims look great on bank one but are nearly +20% on bank 2, which would be LEAN right? I'm so confused. I'll check back in shortly as I am about to hook my friends Tech 2 up and see where the CKP timing is to find out if it jumped a tooth on the dizzy.

Kinda seems like when I hit the throttle (very lightly for obvious reasons) it pops like a back fire through the TB, that's almost always an out of time engine right?

Oh and hutch to answer a previous question, the Spider is an AC Delco from rock auto. Never had problems with the others I've installed.

[Tparkhill]

hooked the scanner up, cylinder 2 and 4 are not firing at all it looks like. The cam advance shows 0 right on the dot, so distributor seems seems fine.

[Hutchinson]

Wow bro,....went from -20 (too much fuel) to +20 (not enough fuel) by simply changing the PCM back to the original black box?? I didn't expect that one bud,...that's a real head scratcher. I'd be walking in circles, kicking big rocks around the yard while low tone mumbling cuss words under my breath (yeah, I've actually done that with a couple previous issues I had),....neighbors were looking at me a bit strange.

Yes Sir, Delphi made most of the stock engine parts for ACDelco, thus, spider's good.

Use the Tech2 to redo the crank relearn if you can. Probably don't need too, but won't hurt. Yes sir, a backfire up through the intake is an out of time engine,...but, engine ran fine before you swapped PCM's,..and dizzy +/-2 setting is dead on zero,....so man that's a tough one to get my head around.
Given what you've observed, it's doubtful your crank/cam timing chain has jumped a tooth. You'd be much worse off than you are if it had jumped a tooth (you'd have troubles in both banks).
If you weren't getting spark in #2 and 4,.....your scanner should show a rich bank 2 and fuel trims would be negative. Fuel would be going in, not getting burned, and subsequently exiting exhaust,....thus showing rich on the bank2 O2 sensor. Yet, scanner is showing your PCM trying to add fuel (+20 LTFT),....... But, you indicated your #2&4 plugs looked good the other day (8 showed bad black/fuel),....wow.

Man, this is confusing as hell bro,....wish I could pull a rabbit outta my hat,.....but, sounds like it's time for a mechanic to look at it, now that you've got the original PCM back in it. At least diagnose it for you/you can fix it. Truly wish I had an answer for you man,......but, drawing blanks because of all the variables/possibilities.

[Tparkhill]

I cant blame you for not knowing, this is an insane problem that appears to be jumping around every time I get close to it.... This thing has literally blown my mind.

And I should correct myself, the cylinders that are missing are still 2 & 8. not 2 & 4

I pulled the valve cover off bank 2 and watched the valves open and close ALL the way so no problems there.
I'll post a video of my scanner and the valves in a bit.

I popped the TB off and stuck a mirror in the plenum to check for fuel all over and its completely DRY inside the plenum but smell TERRIBLY of fuel (WTF!!!) how can it run lean but smell like ungodly amounts of fuel but show LEAN +20% trims on bank 2?

I'm going to be taking it to a shop here soon. I'll let y'all know what happens.....

[Tparkhill]

Finally convinced myself to pull the Dizzy, I wish I would have just started out with that in the first place. the gears are paper thin.... I'll update when the Summit Dizzy shows up.

[Hutchinson]

Cool bud,....consider going to gmtruckcentral.com for the dizzy install procedure from Aloicious. His procedure works perfectly,.....you'll see many people have done it this way and congratulated him on the thread/write up. It sets it perfect the first time.

Still wondering why the PCM is trying to add +20 fuel though,....puzzling. You'd think the opposite. Yes sir, please keep us updated,....lots of people could learn a lot from this.

[Earwax]

Check the distributor gear on the cam.It is also worn.
Check all the plugs.
Replace the plugs that are fouled.2,8?
Fouled plugs screw up the fuel trims due to unburnt fuel.
See if the oil smells like gas,change it if needed.
You should use a real spark tester.
This type will simulate the electrical load that the plug needs.

http://i926.photobucket.com/albums/a...tos/kd2756.jpg

[Hutchinson]

Tpark, these are good points Earwax provides to help you. Smell your dipstick to see if it has ANY fuel smell to it.

Also, the real spark plug tester,....I gotta admit, I'd never seen a spark tester like the one on your video posted couple days ago. I've always just pulled the plug, connected it back to the plug wire, and grounded the spark plug to the block somewhere,....while carefully holding it/having someone roll the engine over a few times. Yeah, it's lite me up a couple times over the years,... but, gotta be tough when yer dumb, I guess. I like the spark tester Earwax provided,.....man, sure simplifies things.

Earwax,....whatcha reckon why he went from -20 (PCM pulling fuel/running rich) to +20 (adding fuel/running lean) by simply swapping out the PCM back to his original black box? Notwithstanding the dizzy/cam gearing,...seems if he didn't have any spark in #4 and 8, it would show running rich without question,.....that's the part that's puzzling me. Yet, his bank2 O2 is reading lean (trying to pull fuel)??? Knuckle dragging dumb look on my face after I heard that one.

[Earwax]

His B2 S1 O2 is stuck lean around 350-400mv.
It is adding fuel trying to richen it up.
Probably due to the dead cylinders on B2.With that much slop in the dist/cam gears it will fire the wrong cylinder.
Chances are that the O2 in B2 is also full of carbon.
The EGR valve also needs a more permanent repair done.
It may be causing an internal vacuum leak.
I did not see a log where it was removing 20% fuel?

[IARLLC]

Since the path of electricity through these distributor caps cross-cross sometimes they burn through and start cross-firing. I have seen it several times.