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Bank 2 exhaust extremely hot, very rough idle, rpms hunting

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Bank 2 exhaust extremely hot, very rough idle, rpms hunting

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Old 07-09-2018, 04:06 PM
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Bank 2 exhaust extremely hot, very rough idle, rpms hunting

Hello all! I’ll try to keep this short, but I’ll start with a bit of background info. I bought a 1976 Chevy K10 with a 350 tpi out of a 1992 camaro awhile back. Didn’t run great but I’m in the mentorship stages of my career as a Chevy tech and was looking for a project. After a few weeks of driving it lost almost all driveability, pulled my plugs and the plug for cylinder 6 was toast. The plug was severely mangled, it had been beaten on badly. Pulled the head and determined motor was toast and replaced it with a reman. Replaced almost everything in the process.

When all was said and done I started it up and let it run for about 10 mins to ensure proper operation. To my disappointment, it ran like a one legged man. Decided to start with setting timing and idle speed. Had trouble setting timing due to fluxuating RPMs and determined something bigger was going on.

From there I determined that I’m most likely running lean on bank 2. Found exhaust from bank 2 is extremely hot and dark, while bank 1 is clear and cool. Headers on bank 2 get almost too hot to touch immediately after starting. Before swapping in the new motor I noticed that the exhaust from bank 2 was producing a lot of smoke on cold mornings compared to bank 1. I chalked it up to the hole in the #6 piston and the disgusting fuel injectors I pulled off the old motor. But both of those problems have been taken care of. I’ve got 45psi in the fuel rail and bank 1 seems to be operating normally, so that tells me I’ve got spark, air, and good fuel lines/rail/pump/injectors.

Tested at injectors #1 and #4 with a noid light and found the light to be bright and flashing, normal operation as far as I can tell. I should test all the other injector connectors, but sense this system is batch fire, and the bank 2 header feels to be a consistent temperature throughout, I’m not really sure if it would be worthwhile, and I don’t want to let it run for too long and risk damage to the new motor.

My gut is telling me the ECM is shot, but I don’t know how to verify this. Part of me just wants to buy an ECM and engine wiring harness and call it a day because evidence is telling me my problem is in one of those two things. However, that’s a pretty penny to spend blindly, and I know that I have the skill set to diagnose and pinpoint my problem.

Where should I go from here? Why am I running lean on bank 2?

In the mean time I am going to use the noid light on the rest of the connectors, test my injector fuses, search for a vacuum leak, inspect my plugs, and drink a beer. I didn’t do a great job at keeping this short, but thank you for reading!


EDIT: After spending some time kicking myself, I realized that bank 2 is running rich, not lean. I'm not sure how I overlooked that. I determined this by reading the plugs per Tuned Performance's suggestion. I found that the plugs for bank 2 are coated in a dry soot, while bank 1 plugs are cleaner and have un-burnt fuel on them. The passenger side exhaust is coated with soot as well. I go into more detail down below. I will hopefully be able to post some updates tomorrow!

Last edited by ChevyK10; 07-10-2018 at 03:22 AM.
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Old 07-09-2018, 04:16 PM
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Re: Bank 2 exhaust extremely hot, very rough idle, rpms hunting

The ecm has one injector driver for both banks. Can you narrow it down to cylinders. You might have plugged injectors.
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Old 07-09-2018, 06:44 PM
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Re: Bank 2 exhaust extremely hot, very rough idle, rpms hunting

Originally Posted by Tuned Performance View Post
The ecm has one injector driver for both banks. Can you narrow it down to cylinders. You might have plugged injectors.

I replaced my injectors, so hopefully theyíre not clogged up already, but theoretically if I had plugged injectors would I have a higher pressure reading at the fuel rail? I have a gauge installed on the rail, so Iíll double check that my pressure reading is within spec. How would you suggest I narrow it down to cylinders?
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Old 07-09-2018, 06:49 PM
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Re: Bank 2 exhaust extremely hot, very rough idle, rpms hunting

Disabling the injector electricity will not effect fuel rail pressure.
You can read your plugs or use a infrared gun to pinpoint which cylinders are running lean. Point the gun at the exhaust ports on each tube of the headers with the engine running.
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Old 07-09-2018, 07:27 PM
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Re: Bank 2 exhaust extremely hot, very rough idle, rpms hunting

Originally Posted by Tuned Performance View Post
Disabling the injector electricity will not effect fuel rail pressure.
You can read your plugs or use a infrared gun to pinpoint which cylinders are running lean. Point the gun at the exhaust ports on each tube of the headers with the engine running.

Alright, I just read up on the fuel system operation a bit to see if fuel rail pressure would be changed by a clogged injector, and from my understanding the fuel rail pressure regulator would correct high fuel rail pressure. So, if I am not mistaken a clogged injector would not cause a higher than normal pressure in the fuel rail? I'm going to measure what temp I'm getting at each exhaust port after running the motor for a couple minutes and get back with you. I'm gonna see if I have something laying around that'll give me an accurate temp reading and if not run over to Advanced Auto Farts and pick up an infrared thermometer. I think I've got the thermometer leads for my DVOM in my toolbox at work. Thank you so much for your help!
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Old 07-10-2018, 12:24 AM
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Re: Bank 2 exhaust extremely hot, very rough idle, rpms hunting

So, I let the motor idle for about a minute and measured the temp at each exhaust port on the header.
Cyl 2: 185F
Cyl 4: 275F
Cyl 6: 245F
Cyl 8: 205F
Bank 1 measured consistently throughout at around 160F. Pulled the plugs from cylinders 1 and 2 and found plug 2 to be very dark and sooty, while plug 1 is still a bit dark for having only about an hour of run time it is considerably cleaner compared to plug 2. I was pretty surprised about that. I inspected the ends of both sides of the exhaust and found the bank 2 side to be very sooty, bank 1 side is pretty clean.

I now understand the importance of keeping an open mind while doing diagnosis. Someone told me that I'm probably running lean on bank 2, and I took that idea and ran. The soot in the exhaust and on the plug tells me I'm most likely running rich on bank 2. My current setup only has an O2 sensor on the driver's side exhaust. This has me thinking that maybe I'm actually running lean on bank 1 (or that the ECM thinks so) and its dumping fuel into my motor, causing bank 2 to run rich and go unnoticed by the ECM. Am I wrong to assume that bank 2 is running rich rather than lean?

I'm kicking myself quite hard at the moment, but I'm going to do some poking around before getting my mind set on any other verdicts. Jumping to unfounded conclusions set me back a good bit, probably could have had this motor road worthy by now if I just had kept an open mind. Almost bought an ECM and wiring harness for no good reason. Sorry for possibly wasting your time, although I probably would not have thought to read my plugs if not for your suggestion. Please don't hesitate to tell me if you think I'm still jumping the gun!! My mentor at work is constantly telling me to slow down and think, hopefully it'll sink in one of these days.

God only knows why, but I never replaced my O2 sensor, I'm going to start with that (probably should have started with that to begin with). I'm going to remove and inspect all of my spark plugs and make sure I didn't mix any of the wires up on the cap. My gut is still telling me that I'm leaking vacuum somewhere even though I've already checked with throttle body cleaner. Going to re-check for vac leaks with propane gas, more TB cleaner, and if I'm still not satisfied I'll smoke test it.

Is there anything else you can think of that I should check out? Any ideas on why cylinder 4 is reading so much higher than the others? A coworker offered to let me bum his snap-on scan tool for a day, looking forward to reading into my sensor values. I'm going to update my original post with this information. Thank you again for your help, this is my first personal project car and experience working with a TPI. Without help from folks like you, I'm not sure if I'd be able to manage this project and I'm grateful beyond words.
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Old 07-10-2018, 01:49 PM
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Re: Bank 2 exhaust extremely hot, very rough idle, rpms hunting

A o2 is super cheap for a 1 wire. In headers it’s good to run a heated o2 like a afs-74 delco. The headers often don’t get up to 5-600 f the temperature the o2 needs to be at to become active. I don’t think the o2 is the issue. On a batch injection system all cylinders receive the same amount of fuel.
Did you get the injectors from southbay and are they Bosch 3s ?


Post 15 on how to build a pigtail for a heated o2
https://www.thirdgen.org/forums/cool...-what-fan.html

Last edited by Tuned Performance; 07-10-2018 at 02:17 PM.
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Old 07-10-2018, 06:10 PM
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Re: Bank 2 exhaust extremely hot, very rough idle, rpms hunting

Originally Posted by Tuned Performance View Post
A o2 is super cheap for a 1 wire. In headers itís good to run a heated o2 like a afs-74 delco. The headers often donít get up to 5-600 f the temperature the o2 needs to be at to become active. I donít think the o2 is the issue. On a batch injection system all cylinders receive the same amount of fuel.
Did you get the injectors from southbay and are they Bosch 3s ?


Post 15 on how to build a pigtail for a heated o2
https://www.thirdgen.org/forums/cool...-what-fan.html

Turns out I already have a heated o2, uses the o2 for a bronco, feeling kind of skeptical of that. Not very confident in really any of the wiring the previous owner did. I smoked out my intake last night and found a leak in the booster hose, and smoke was also dumping out of the IAC valve between the head and connector area, not sure if thatís normal but I went ahead and replaced it anyway.

The injectors i bought were from napa, Iíll check my receipts and double check who makes them, I just know right now that I got the OE equivalent. Was that a bad choice?
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Old 07-10-2018, 07:13 PM
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Re: Bank 2 exhaust extremely hot, very rough idle, rpms hunting

I don’t know Napa’s quality as far as injectors go.
The ones South Bay fuel injectors sell have been known to run the engine just a little lean.
Not like as bad as your experiencing unless they are slightly plugged. The iac shouldn’t have a leak on the body of it. That small of a leak shouldn’t effect anything . I’m at a loss on what’s causing the lean condition on one bank. Unless you move around the injectors to see if the lean condition follows esp #4 cylinder.
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Old 07-10-2018, 07:25 PM
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Re: Bank 2 exhaust extremely hot, very rough idle, rpms hunting

Originally Posted by Tuned Performance View Post
A o2 is super cheap for a 1 wire. In headers itís good to run a heated o2 like a afs-74 delco. The headers often donít get up to 5-600 f the temperature the o2 needs to be at to become active. I donít think the o2 is the issue. On a batch injection system all cylinders receive the same amount of fuel.
Did you get the injectors from southbay and are they Bosch 3s ?


Post 15 on how to build a pigtail for a heated o2
https://www.thirdgen.org/forums/cool...-what-fan.html
Originally Posted by Tuned Performance View Post
I donít know Napaís quality as far as injectors go.
The ones South Bay fuel injectors sell have been known to run the engine just a little lean.
Not like as bad as your experiencing unless they are slightly plugged. The iac shouldnít have a leak on the body of it. That small of a leak shouldnít effect anything . Iím at a loss on whatís causing the lean condition on one bank. Unless you move around the injectors to see if the lean condition follows esp #4 cylinder.
I pulled off the valve covers to make sure the TDC I used when I installed the dizzy was actually TDC. Looks like thereís a chance I was about 30 degrees retarded... I installed a remote starter and bumped the motor until cylinder 1 exhaust started to open, backed it off and put a zip tie into the plug hole, rotated clockwise until the zip tie stopped moving. Is that an okay method? Should I remove and reinstall the dizzy?
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Old 07-10-2018, 07:35 PM
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Re: Bank 2 exhaust extremely hot, very rough idle, rpms hunting

Post #7 is how I find tdc.
Not sure what stroke you where on when you put the zip tye in the cylinder.
Sounds like you rotated it from exhaust stroke to compression.
https://www.thirdgen.org/forums/tech...ion-leads.html
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Old 07-11-2018, 11:29 PM
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Re: Bank 2 exhaust extremely hot, very rough idle, rpms hunting

I think you are smart to verify the O2 is sending the right signal. Timing and firing order double checks also smart because that is a free check.
But it's weird the issues seem to be one bank only. Could this be a restrictive exhaust/plugged cat or similar on one side only?
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Old 07-17-2018, 07:12 PM
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Re: Bank 2 exhaust extremely hot, very rough idle, rpms hunting

Originally Posted by Bow_Tied View Post
I think you are smart to verify the O2 is sending the right signal. Timing and firing order double checks also smart because that is a free check.
But it's weird the issues seem to be one bank only. Could this be a restrictive exhaust/plugged cat or similar on one side only?

Sorry for the late reply, I've been super busy. That seems like it could be in the realm of possibilities, I've got cats on it and if there was a restriction in the exhaust on that side, I'd bet it be at the cat. I'll have to pull the cats off and see what kind of condition they're in. I'll probably end up ditching them while I have them out either way hahaha!
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Old 07-21-2018, 11:25 AM
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Re: Bank 2 exhaust extremely hot, very rough idle, rpms hunting

This sounds like a typical single bank exhaust restriction situation to me. The computer assumes both banks are breathing equally and if they are not it will skew the mixtures rich on one bank and lean on the other bank. That, coupled with the previous engine having an internal failure that damaged a plug and likely sent shrapnel down the exhaust... I would bet on a plugged exhaust on one bank.

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