Lean under WOT
Thread Starter
Intermediate
Joined: Dec 2024
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Lean under WOT
1998 C5, 80lb inj, 525 pump w/ hot wire kit, E85, 10-11 psi max on single rear mount. It's on a 2barOS. I'm running lean above 4k RPM it stays at 11-12 AFR then shoots to 13-15. I reused intake manifold seals could that be causing my issue? I also suspect the fuel filter might be a problem since I haven't changed it yet. I'm getting blow by out of the dipstick too only in boost which I feel is from not having a catch can but could be wrong.
Gonna compression check for ringlands. Any other suggestions or thoughts?
Gonna compression check for ringlands. Any other suggestions or thoughts?
Moderator, Tech Contributor
Joined: Sep 2013
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From: Cape Coral, Florida
Look at your long term fuel trims…if elevated above 10% run the engine at 3000 RPM for a few minutes…if long terms decrease you have a vacuum leak…if still lean under load and no vacuum leak with scan tool look at your upstream O2 at WOT…upstream should go rich near 900mv’s…if not fuel delivery (fuel pump, fuel filter) or MAF.
Thread Starter
Intermediate
Joined: Dec 2024
Posts: 26
Likes: 3
Look at your long term fuel trims…if elevated above 10% run the engine at 3000 RPM for a few minutes…if long terms decrease you have a vacuum leak…if still lean under load and no vacuum leak with scan tool look at your upstream O2 at WOT…upstream should go rich near 900mv’s…if not fuel delivery (fuel pump, fuel filter) or MAF.
Moderator, Tech Contributor
Joined: Sep 2013
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From: Cape Coral, Florida
Tech Contributor
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From: Dyer, IN
Running Guns & Moonshine
Joined: Aug 2001
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From: CT
I had similar issue once. I went down a list of options from swapping Maf, new Map, (never thought to check O2s for this circumstance), and in my case it ended up being the pump by way of a poor quality ground. I refreshed the ground on the driver rear and everything was aces.
I have also once had a bad string of pumps from Racetronix. You didn't buy from them, did you? And you're sure you don't have the China knock-off of your Walbro / TI Automotive pump?
I have also once had a bad string of pumps from Racetronix. You didn't buy from them, did you? And you're sure you don't have the China knock-off of your Walbro / TI Automotive pump?
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Thread Starter
Intermediate
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Would you know why my wideband is reading extremely lean but I can smell the E85 and it’s backfiring. I have 0 power when it does this obviously but normal cruising AFR is 11-12 then when i step on it to get it into boost it spikes up to 16-18. I regapped my plugs to .25-.27 already.
Thread Starter
Intermediate
Joined: Dec 2024
Posts: 26
Likes: 3
I had similar issue once. I went down a list of options from swapping Maf, new Map, (never thought to check O2s for this circumstance), and in my case it ended up being the pump by way of a poor quality ground. I refreshed the ground on the driver rear and everything was aces.
I have also once had a bad string of pumps from Racetronix. You didn't buy from them, did you? And you're sure you don't have the China knock-off of your Walbro / TI Automotive pump?
I have also once had a bad string of pumps from Racetronix. You didn't buy from them, did you? And you're sure you don't have the China knock-off of your Walbro / TI Automotive pump?
Thread Starter
Intermediate
Joined: Dec 2024
Posts: 26
Likes: 3
Thread Starter
Intermediate
Joined: Dec 2024
Posts: 26
Likes: 3
Heres 2 logs, 2nd log I was able to open it up more. I think you can see where it starts backfiring in the log, it just falls flat on its face when it does it and hits like 18 AFR on WB. No front O2s on it and its on 2 bar cobalt ss map. Also want to add its barely making boost (like 3-7 PSI Max) do to it backfiring how it is and I do have a small boost leak on my BOV weld that needs to be fixed.
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Intermediate
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No way it’s hitting 16 psi realistically, do you think the map sensors bad or what would cause it to read like that? Also do you think its just dumping fuel in due to the map reading that much causing a false lean? I still need to get tune revisions but trying to get all my problems sorted out before I do that.
Last edited by Blayn; Jan 14, 2025 at 12:17 AM.
Melting Slicks
Joined: Nov 2013
Posts: 2,049
Likes: 316
From: USA
I really don't know where to start, not nearly enough info posted to make any sort of recommendation.
Are you getting tuned at a shop? online?
How are you reading AFR, I don't see it in the log, just a standalone gauge? What gauge? Hook it up to VCM scanner if possible, makes logging so much better.
How else are you reading MAP/boost? Standalone gauge? What MAP sensor are you using? What's the scaling? Do you have the tune file?
Gotta get the hardware stuff sorted first and get the basic sensors working correctly before can really get any idea what is actually going on.
Are you getting tuned at a shop? online?
How are you reading AFR, I don't see it in the log, just a standalone gauge? What gauge? Hook it up to VCM scanner if possible, makes logging so much better.
How else are you reading MAP/boost? Standalone gauge? What MAP sensor are you using? What's the scaling? Do you have the tune file?
Gotta get the hardware stuff sorted first and get the basic sensors working correctly before can really get any idea what is actually going on.
Thread Starter
Intermediate
Joined: Dec 2024
Posts: 26
Likes: 3
I really don't know where to start, not nearly enough info posted to make any sort of recommendation.
Are you getting tuned at a shop? online?
How are you reading AFR, I don't see it in the log, just a standalone gauge? What gauge? Hook it up to VCM scanner if possible, makes logging so much better.
How else are you reading MAP/boost? Standalone gauge? What MAP sensor are you using? What's the scaling? Do you have the tune file?
Gotta get the hardware stuff sorted first and get the basic sensors working correctly before can really get any idea what is actually going on.
Are you getting tuned at a shop? online?
How are you reading AFR, I don't see it in the log, just a standalone gauge? What gauge? Hook it up to VCM scanner if possible, makes logging so much better.
How else are you reading MAP/boost? Standalone gauge? What MAP sensor are you using? What's the scaling? Do you have the tune file?
Gotta get the hardware stuff sorted first and get the basic sensors working correctly before can really get any idea what is actually going on.
Melting Slicks
Joined: Nov 2013
Posts: 2,049
Likes: 316
From: USA
Biggest red flag is the MAP scaling in the tune. I used to run this one but I can't find the file anymore, but I searched HPT forum and this sensor scaling should be 200/8. Linear/Offset respectively.
A quick way to test this is key on, engine off. turn on VCM scanner, check MAP. It should be around 100 kPa at sea level.
Definitely need to get this sorted/fixed, if that is off everything else will be useless garbage. It would definitely explain the boost/MAP discrepancy too.
It's likely you're still running out of fuel, but need to get MAP sorted first.
As for the Wideband... C5 is before CANbus was a thing so that one won't work. I'm not real smart on AEM sensors, but if it has a way to output serial, you can easily connect that to laptop to log it. Or last resort is analog output, you can wire that into the EGR port of the PCM which is normally open and not used. Set up a custom scaling in scanner and you can log wideband anytime. I have an Innovate LC-2, but I do this.
In the meantime you can do the key on, engine off MAP test and adjust the MAP sensor scaling, if required.
A quick way to test this is key on, engine off. turn on VCM scanner, check MAP. It should be around 100 kPa at sea level.
Definitely need to get this sorted/fixed, if that is off everything else will be useless garbage. It would definitely explain the boost/MAP discrepancy too.
It's likely you're still running out of fuel, but need to get MAP sorted first.
As for the Wideband... C5 is before CANbus was a thing so that one won't work. I'm not real smart on AEM sensors, but if it has a way to output serial, you can easily connect that to laptop to log it. Or last resort is analog output, you can wire that into the EGR port of the PCM which is normally open and not used. Set up a custom scaling in scanner and you can log wideband anytime. I have an Innovate LC-2, but I do this.
In the meantime you can do the key on, engine off MAP test and adjust the MAP sensor scaling, if required.
Thread Starter
Intermediate
Joined: Dec 2024
Posts: 26
Likes: 3
Biggest red flag is the MAP scaling in the tune. I used to run this one but I can't find the file anymore, but I searched HPT forum and this sensor scaling should be 200/8. Linear/Offset respectively.
A quick way to test this is key on, engine off. turn on VCM scanner, check MAP. It should be around 100 kPa at sea level.
Definitely need to get this sorted/fixed, if that is off everything else will be useless garbage. It would definitely explain the boost/MAP discrepancy too.
It's likely you're still running out of fuel, but need to get MAP sorted first.
As for the Wideband... C5 is before CANbus was a thing so that one won't work. I'm not real smart on AEM sensors, but if it has a way to output serial, you can easily connect that to laptop to log it. Or last resort is analog output, you can wire that into the EGR port of the PCM which is normally open and not used. Set up a custom scaling in scanner and you can log wideband anytime. I have an Innovate LC-2, but I do this.
In the meantime you can do the key on, engine off MAP test and adjust the MAP sensor scaling, if required.
A quick way to test this is key on, engine off. turn on VCM scanner, check MAP. It should be around 100 kPa at sea level.
Definitely need to get this sorted/fixed, if that is off everything else will be useless garbage. It would definitely explain the boost/MAP discrepancy too.
It's likely you're still running out of fuel, but need to get MAP sorted first.
As for the Wideband... C5 is before CANbus was a thing so that one won't work. I'm not real smart on AEM sensors, but if it has a way to output serial, you can easily connect that to laptop to log it. Or last resort is analog output, you can wire that into the EGR port of the PCM which is normally open and not used. Set up a custom scaling in scanner and you can log wideband anytime. I have an Innovate LC-2, but I do this.
In the meantime you can do the key on, engine off MAP test and adjust the MAP sensor scaling, if required.
I’ve read on the EGR port wiring which I will probably end up doing eventually.
Melting Slicks
Joined: Mar 2018
Posts: 2,502
Likes: 187
From: California
The map seems faulty if not the map someone ripped you on the tune . Some advise . Get a gm 2 bar sensor I forget the part number but the guys should have it here . Wouldn’t hurt to get a hpt device . I could make it run after that pretty dam well but you would need a deka 60 injector .