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New LQ9 Build stumble at half throttle

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Old 06-25-2018, 06:31 PM
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Default New LQ9 Build stumble at half throttle

2000 GMC scsb with a fresh LQ9 build (with 60 driving miles), cam, headers (no cats) with 50 lb/hr flex injectors and PCM tune by Frost. Truck fires right, up idles well but at mid throttle it stumbles. Sometimes I can power through the stumble and the engine runs strong. It has a rich smell at idle that actually burns my eyes. Code reader finds no DTC codes. The downstream o2's are tuned out but the scanner only sees "Bank 1 sensor 1". When I check "Bank 2 sensor 1" the scanner reads "not supported". It is a cable driven return type fuel rail with the regulator on the rail. Brand new AC-Delco throttle body with new IAC & TPS sensors.

Besides the engine stumble/miss, I'm concerned about the o2 Bank 2 sensor not showing on the scanner. Could this have been accidentally removed in the tune. Could a bad o2, not throw a code, not show up on the scanner but still need replacing?

Engine stumble @ 0:05. Then a clean pull to 5000

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Old 06-25-2018, 08:16 PM
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What cam do u have in there. You should jave Frost adjust your EOIT to get rid of that fuel smell at idle...

Sounds to me that you prob need a real tune insread of a mail order...
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Old 06-25-2018, 08:26 PM
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Originally Posted by jayyk31 View Post
What cam do u have in there. You should jave Frost adjust your EOIT to get rid of that fuel smell at idle...

Sounds to me that you prob need a real tune insread of a mail order...
228/230 .585/.585 112*

I agree on the in person tune. Just curious on my handheld scanner not seeing the bank 2 o2.

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Old 06-25-2018, 09:48 PM
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Call Frost. He has great customer support.
Let him know what is going on and let him help you.
Have you done this?
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Old 06-25-2018, 10:19 PM
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Originally Posted by sowbelle View Post
Call Frost. He has great customer support.
Let him know what is going on and let him help you.
Have you done this?
I replied to the email he sent about the issue (when he shipped the PCM). I guess you're right, should give him a call.

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Old 06-28-2018, 11:33 AM
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You have to figure out your 02 problem first. That is most likely your stumble problem. How does it run cold before it goes into closed loop?
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Old 06-28-2018, 11:48 AM
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I had similar issue after new build and base tune installed. Just did idel first and stumbled trying to get into 3000+ range. I added a 10% across the board in VE to just get into it but still stumbled on first test.

It was the fuel pressure and IFR. Just changed the IFR from stock of 92.5 @58 . I was actually at 65PPSI so I scaled it up. (which means less fuel) to 97.7
Bam instant WOT no knock.
Check your Fuel Pressure and IFR for those 50lbs'rs
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Old 06-28-2018, 12:21 PM
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Originally Posted by gagliano7 View Post
You have to figure out your 02 problem first. That is most likely your stumble problem. How does it run cold before it goes into closed loop?
New Denso o2's will be here tomorrow. It still has the mid throttle stumble when cold. I never see any black exhaust but you can really smell the burnt rich fuel. My garage stinks of it, I guess it has permeated the packing inside both mufflers. I'll report back after the new o2's are installed.

Steve (Frost) replied to my e-mail
Originally Posted by Tuned by Frost
When the vehicle works right, it corrects it's own fuel everywhere (everywhere) except for 2-3 seconds of first crank and until you go WOT. You can't "remove" anything of the sort (Bank 2 Sensor 1) like that in a tune (ie one side's closed loop ability). Drop the code reader and trouble shoot by looking at scan data. What are the trims on each back doing as it runs (the misfiring side or sides will trim falsely high... that fuel the ECM adds is what you see and smell)? What are the raw voltages on the O2s during this? You should be able to tell which side doesn't switch properly there as well (though it's the side or sides that plugs get blacked). You can't sit and wait for codes; it's not a stock vehicle, and without a stock cam there is no misfire detection like an OEM car. Fouled plugs come from a misfire, bad O2 or cabling, or exhaust leak... always.... because the vehicle trims (corrects) it's own fuel. This is what closed loop is. If part of that system doesn't work right, it's (usually very) obvious from rough running (so seriously; don't drive it, fix it), smelling like raw fuel, and blacking plugs, popping during steady throttle; etc.. It's not going to just go away. If you do not use the correct tools to diag this, all you can do is keep heaping parts on (front O2s and plugs)... but there is some culprit to find. Not sure where you are located but I'd be happy to get it fixed and go over the tune in person if you want to get the truck over.

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Old 06-28-2018, 12:32 PM
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Originally Posted by Jim Cuff View Post
I had similar issue after new build and base tune installed. Just did idel first and stumbled trying to get into 3000+ range. I added a 10% across the board in VE to just get into it but still stumbled on first test.

It was the fuel pressure and IFR. Just changed the IFR from stock of 92.5 @58 . I was actually at 65PPSI so I scaled it up. (which means less fuel) to 97.7
Bam instant WOT no knock.
Check your Fuel Pressure and IFR for those 50lbs'rs
I'm an old (really old) school carburetor and distributor guy... you're talking a language I mostly don't understand. I really need someone local that can hold my hand in this uncharted foreign EFI land.
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Old 06-29-2018, 07:23 AM
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Originally Posted by RedXray View Post
New Denso o2's will be here tomorrow. It still has the mid throttle stumble when cold. I never see any black exhaust but you can really smell the burnt rich fuel. My garage stinks of it, I guess it has permeated the packing inside both mufflers. I'll report back after the new o2's are installed.

Steve (Frost) replied to my e-mail
With the one 02 not reading it could be dumping fuel. Do you have tuning software? Can you see what the one 02 sensor that is working is reading lean or rich? If you could force it into open loop so its not using the 02 sensors instead it uses VE and MAF then you will no if the 02's are causing the problem.

Also when you go WOT the 02's aren't controlling anything.
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Old 06-29-2018, 03:10 PM
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Originally Posted by gagliano7 View Post
With the one 02 not reading it could be dumping fuel. Do you have tuning software? Can you see what the one 02 sensor that is working is reading lean or rich? If you could force it into open loop so its not using the 02 sensors instead it uses VE and MAF then you will no if the 02's are causing the problem.

Also when you go WOT the 02's aren't controlling anything.
No tuning software. New o2's no change. Ran propane along the vacuum lines and intake no leaks. Going to bypass the evap and pcv to make sure it's not sucking air and check right bank o2 for voltage at the harness.

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Old 06-29-2018, 08:02 PM
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Changed MAP sensor to known good one... no change. The Flex Fuel 50 lb/hr injectors were rebuilt maybe they are junk. Tempted on putting the OEM camshaft and 24lb injectors back in and finding a stock PCM.
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Old 06-30-2018, 06:11 PM
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Originally Posted by RedXray View Post
Changed MAP sensor to known good one... no change. The Flex Fuel 50 lb/hr injectors were rebuilt maybe they are junk. Tempted on putting the OEM camshaft and 24lb injectors back in and finding a stock PCM.
That IMO would be foollish after investing what you have in upgrades. Bite the bullet and find a local good tuner. If you can't find one local, then tow it to one within a reasonable distance. Or drive it as long as it isn't running too rich or too lean.

It can be frustrating to say the least, but the knowledge base today concerning how to tune these cars along with the good software available to get it done, there is no reason why a good tuner can't get you running. But when you find a tuner, make sure to have the understanding that you want driveability. With that cam and if you haven't changed the torque converter, it should drive almost like stock, and be a blast to drive.
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Old 06-30-2018, 07:02 PM
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Don't give up and go back. Find a way to make it happen. I think you either need to find a local tuner like it has been stated, or, learn to tune yourself. Tuning isn't really that difficult once you get to where you know what questions to ask, a lot of the answers you need you can find from simply searching the web. I am always still learning the EFI thing myself, I feel that even once one gets over the difficult part of the learning curve you encounter in the beginning, there is still something left to learn no matter your skill/knowledge level.

I just put a sloppy stage 2 cam in my turbo LQ4. I drove it around with just the turbo on the stock LQ4 but recently tossed the cam in it. Still gotta sort out the details on dialing in the new cam in the tune but it's super worth it. I will likely be asking questions here on pointers and clarifications on tuning my new cam.

I will say this as far as injectors. Don't know how critical it is for a N/A build, but on my S475 LQ4 I wanted to use decapped truck injectors. Wanted to use them for the fact that they are cheap (free) and it fully embraces the spirit of hotrodding by using rusty junk that you already have laying around instead of buying a bunch of ****. I had to decap and flow test some 30 odd injectors to find a set of 8 that were matched. You might think about flow testing the injectors you have, could be a portion of what's going on is erratic fueling. I don't think the spread of flow values matters on a stockish LS, but with even a slight emphasis on performance it becomes more critical I think.
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Old 07-01-2018, 08:51 AM
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Originally Posted by ElQueFør View Post
Don't give up and go back. Find a way to make it happen. I think you either need to find a local tuner like it has been stated, or, learn to tune yourself. Tuning isn't really that difficult once you get to where you know what questions to ask, a lot of the answers you need you can find from simply searching the web. I am always still learning the EFI thing myself, I feel that even once one gets over the difficult part of the learning curve you encounter in the beginning, there is still something left to learn no matter your skill/knowledge level.

I just put a sloppy stage 2 cam in my turbo LQ4. I drove it around with just the turbo on the stock LQ4 but recently tossed the cam in it. Still gotta sort out the details on dialing in the new cam in the tune but it's super worth it. I will likely be asking questions here on pointers and clarifications on tuning my new cam.

I will say this as far as injectors. Don't know how critical it is for a N/A build, but on my S475 LQ4 I wanted to use decapped truck injectors. Wanted to use them for the fact that they are cheap (free) and it fully embraces the spirit of hotrodding by using rusty junk that you already have laying around instead of buying a bunch of ****. I had to decap and flow test some 30 odd injectors to find a set of 8 that were matched. You might think about flow testing the injectors you have, could be a portion of what's going on is erratic fueling. I don't think the spread of flow values matters on a stockish LS, but with even a slight emphasis on performance it becomes more critical I think.
I agree that buying your own software to learn how to tune is good.

However, if you don't plan to continue to make upgrades, then the cost for the software for one license is almost the cost of a paying a tuner to get you going and running in just a few hours leaving you with software you might not use very often if ever.

That said, more power is addictive, so it is likely you will be making upgrades which will require slight modifications to your tune. So purchasing EFI or HPT software might be the most economical route to follow. A couple dyno sessions along with tuning during each can get very expensive in a hurry.

This site sells a file (a step by step electronic book) which if you followed probably would get you a near perfect tune. IMO, however, the samples are more geared to HPT (HP tuners) than EFI. The link below is an example of how-to's online to help you if you decide to purchase your own software.

http://www.masterenginetuner.com/

Click on the link 'More Tuning Tips'. It applies to your mods.

hth
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Old 07-01-2018, 06:59 PM
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I've been fortunate enough that what I couldn't figure out on my own through internet searches and trial and error, I have been able to ask questions on this board and get help from some guys. Which I appreciate immensely and I try to pay it forward if and whenever I can.

The most difficult thing for me dialing in my tune was figuring out what values to set in the injector flow rate table. Really was easy in hindsight as setting them to 75# across the board got me where I needed to be. But the learning curve of doing it the first time and the fact that decapped injectors for a 3 bar setup is still kind of on the ragged edge. Most people just slam down the cash for a set of Dekkas or whatever where the data is known.

A lot of people tout the Banish DVD and book. I can't speak for the DVD as I haven't seen it, but the book was pretty disappointing to me. Maybe it's because I was already past that point when I purchased it.

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Old 07-01-2018, 07:16 PM
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Originally Posted by ElQueFør View Post
A lot of people tout the Banish DVD and book. I can't speak for the DVD as I haven't seen it, but the book was pretty disappointing to me. Maybe it's because I was already past that point when I purchased it.
I have the SA Design book Banish wrote. It IS pretty good, but if you already have a solid working knowledge of tuning, then yeah it might be below your knowledge level. Being as old as it is (10 years?) , I wonder if it's due for updating.
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Old 07-01-2018, 07:31 PM
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Yeah it's great for explaining the basics but beyond that it is lacking. I have tinkered with tuning TBI SBCs for years so I had already learned a lot of that. When I started to put together and tune my 3 bar S475 LQ4 I was looking for some information on that. I flipped through it at the bookstore for a bit before I bought it and decided to go ahead with it. It just lacks the subtle details of dialing in a little more involved build I guess.
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Old 07-01-2018, 08:56 PM
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Yeah, once you have the basics from the book(which it provides quite well) you pretty much have to get your feet wet with HPT or EFILive, so you learn by doing.
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Old 07-02-2018, 01:16 PM
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The link that I provided is a StepByStep tuning manual written by Dan Maslic. Dan's first manual isnt nearly as extensive in detail as the second edition electronic file that you download after purchasing. I never mentioned Greg Banish so can't comment on it.

http://www.masterenginetuner.com/

It contains case studies to include a 2007 Corvette, 2006 Chevy SSR, a heavily modified 1998 Camaro SS, a turbocharged 2002 Camaro and a turbocharged LS7-powered Factory Five GTM. The 1998 Camaro case study is perhaps closest to what the OP has in his truck sans converter.

"1998 CHEVROLET CAMARO (page 181 - HP Tuners, page 220 – EFI Live) – performance camshaft, 85mm MAF and LS6 intake manifold, cold air intake, long-tube headers, full-length performance exhaust, nitrous oxide injection - 125 hp".

A wasted set of plugs and a tank of gas will more than pay for the file. IMO will also help the OP look at the tables in the software to get a picture of what changes the tuner makes.

And the OP can download free demo's of each software package as well, install it and follow as along as Maslic goes thru each step of the tuning process.

Sounds like Frost is willing to work with the OP. If so he could log some data, send it to Frost perhaps for some tweaks, assuming OP decides to purchase either package and Frost is willing to send files back and forth.
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