Started LQ4 swap for first time and runs really rough, long term fuel trim way off

[ja_engineer]

I have been working on my 1980 Camaro/LQ4 restomod for the past several years and I finally fired it this weekend and it is running really rough. First fire I was getting P0200 code which ended up being a damaged injector pigtail (injector 6) so I repaired that but I am still having a problem with bank 2. I checked remainder of wiring and it appeared good and noid light shows all injectors pulsing. I have attached my tune and two quick logs that I took. At this point I am guessing it is either clogged injectors or bad o2 (but they are brand new ac delco), but I was hoping someone more knowledgeable with Gen III tunes/logs might be able to spot something that I am missing. I really want to take this for a drive since the car hasn't moved under power for around 10 years. Any help is greatly appreciated!

Equipment/Mods:
Stock LQ4 - 2003 Express 3500 donor
Speartech reworked harness
85mm truck maf
long tube headers
segment swap auto to manual

[joecar]

It seems to me that your injectors have problems.

[joecar]

Do you have the FPR that came with the LQ4 (i.e. at the fuel rail)...?

Did you connect the reference hose from the FPR to the intake manifold (vacuum side)...?

Did you measure rail pressure (with FPR manifold-reference hose temporarily removed)...?

[ja_engineer]

Do you have the FPR that came with the LQ4 (i.e. at the fuel rail)...?

Did you connect the reference hose from the FPR to the intake manifold (vacuum side)...?

Did you measure rail pressure (with FPR manifold-reference hose temporarily removed)...?

I do have the stock regulator and the vacuum hose is hooked up but when I checked pressure at the rail I am getting about 80 psi so I may have s bad regulator.



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[joecar]

80 psi may mean that the FPR is not able to dump fuel back into the return line (is return line clogged...?).

[ja_engineer]

It is a new line and I ran some air through it to blow it out after assembly. I will check in the morning if it has gotten linked or something. I recall one of the bends going over the axle deforming some when I bent it but I don't remember it being that significant.


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[ja_engineer]

80 psi may mean that the FPR is not able to dump fuel back into the return line (is return line clogged...?).

I figured out the fuel pressure issue, the regulator on the rail is adjustable and I was able to adjust it down to 58 PSI which smoothed out the car some but it is still running rough. Also if I give it any throttle it starts to surge and stumble and LTFT is still 8.6 on bank 2. I have uploaded two logs. The first one is when I was dialing in the fuel pressure regulator and the second is after I got it adjusted and a gave it a little throttle. I am still thinking injectors but I might try to switch 02's from side to side to see if the issue changes banks. I was looking at the 02 voltage and wondering if it is switching correctly but I am not really sure what it should look like for this engine. Again your help is much appreciated.

[joecar]

Did you adjust the FPR to 58 psi with the reference hose temporarily removed (i.e. FPR exposed to BARO)...?

[joecar]

BTW: you don't have to log that many pids (too many pids reduces the sampling rate).

[ja_engineer]

Did you adjust the FPR to 58 psi with the reference hose temporarily removed (i.e. FPR exposed to BARO)...?

Last night I set it exposed to atmosphere the first time and when I hooked up the vacuum reference it dropped to like 47 psi so I reset it with the reference line hooked up. I didn't expect it to drop that much but after doing some research that appears to be correct. Tonight I reset it based on being exposed to atmosphere and I started unhooking injectors to see the effect. Two injectors on bank two had no effect when being unhooked. I checked with a stethoscope and one of the two was not firing and the other had a faint tick. I Then checked those two connectors again with the noid light and they were both getting pulse signals so I am pretty sure I have a couple bad injectors. I have attached the logs from tonight.

Thanks for your help joecar!

[joecar]

The pressure difference across an injector determines its flowrate...

with an manifold-referenced FPR:
pressure on top = 58 psi + MAP.
pressure on bottom = MAP.
difference = 58 psi = constant

constant pressure difference means IFR table B4001 will be flat.


More precisely, mathematically, see here: Calculating-Injector-Flow-rate (https://forum.efilive.com/showthread.php?4821-Calculating-Injector-Flow-rate)

[ja_engineer]

I swapped injectors out this morning and now the car idles/sounds much better and the fuel trim looks ok to me. However, when I give it a little throttle it starts to stall/stumble and these stumbles are timed to the commanded AFR going from 14.68 to 14.03 when I am looking at the scan tool dashboard. I have uploaded a log of when this occurs. Do you have any ideas what might be causing this?

[joecar]

Looks like transition from base spark table to HO spark table is too great.

[ja_engineer]

I am running the stock tune except for the segment swap to manual, the maf tables for the 85 mm maf (engine did not come with the stock maf) and the new injector data (copied from stock ctz). Based on that I was not anticipating have to adjust spark tables. Do you have a recommendation? I just hooked up the wideband on and it is idling around 16.2 afr and goes leaner with throttle.


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[joecar]

I am running the stock tune except for the segment swap to manual, the maf tables for the 85 mm maf (engine did not come with the stock maf) and the new injector data (copied from stock ctz). Based on that I was not anticipating have to adjust spark tables. Do you have a recommendation? I just hooked up the wideband on and it is idling around 16.2 afr and goes leaner with throttle.


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If it's running from the MAF then the MAF table will need correcting.

The MAF table is sensitive to not only the MAF but also its plumbing.

[ja_engineer]

Is there a general increment to beginning the maf table adjustment? Or do I just go a couple percent at a time until I get a reasonable AFR.


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[joecar]

Take a log, apply the transient filter (to eliminate data during which throttle moved), make a map of average of LTFT1 and LTFT2 (as a BEN), and apply this to the MAF table.

[ja_engineer]

I found that the intake gaskets are leaking and causing bank 1 to go lean so once that is fixed I will work on the maf. With that being said what does "as a BEN" mean?

Thanks


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[joecar]

..., make a map of average of LTFT1 and LTFT2 (as a BEN) ...
Average of LTFT's is (LTFT1+LTFT2)/2 and had units %

this as a BEN (i.e. multiplier) would be 1+(LTFT1+LTFT2)/200 and is unit-less.

[ja_engineer]

Ok so I fixed the vacuum leak and played with the maf table some but I still get this stumble/surge under constant throttle. I have attached a video of it but I can't figure it out.

[joecar]

Ok so I fixed the vacuum leak and played with the maf table some but I still get this stumble/surge under constant throttle. I have attached a video of it but I can't figure it out.Do you have a log file of that...?

[ja_engineer]

I will take one tonight and post it.


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[ja_engineer]

I attached the log showing the surging at constant rpm. I checked the tps and map via the scan tool and they both seem to be fine. I have checked for additional vacuum leaks and have not found any. I noticed tonight that it only seems to occur above about 1000 rpm and the surge seems to get more pronounced with increased throttle/rpm. If I give it a quick rev it will be fine but if I give it successive revs it will cut out and almost die after the first rev.

[joecar]

Interesting... looks like some air/fueling/spark loop... can you post your tune file.

[ja_engineer]

Interesting... looks like some air/fueling/spark loop... can you post your tune file.

Joecar the first file is the current tune that I am using (segment swap, modified maf tables and injectors) and the second file is the original tune extracted from ecu when I first got the engine, which as far as I know is the stock tune.

Thanks for your help!

[ja_engineer]

Joecar do you think it's possible the pcm is bad? Tonight I did a full flash of a 4.8 manual tune (could not find a 6.0 manual tune) and copied in the engine tables and it still did the same. Everything is fine until about 1300 rpm then it starts stumbling like in the video.


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[joecar]

When you did the segment swap, did you do a full flash...?

[joecar]

Do you have another PCM to try...?

[ja_engineer]

Yes I did do a full flash with the segment swap. I only have the the PCM but could look on eBay for another one. I have a spare 512k pcm but not a 1k.


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[ja_engineer]

I full flashed the original auto tune in and disabled all of the auto stuff and it seemed to fix the problem. It will rev fine now. I am going to compare settings/tables between the two and see if I can spot the offending settings. Unless the segment swap some how corrupted the tune?


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[joecar]

I full flashed the original auto tune in and disabled all of the auto stuff and it seemed to fix the problem. It will rev fine now. I am going to compare settings/tables between the two and see if I can spot the offending settings. Unless the segment swap some how corrupted the tune?


Sent from my iPhone using TapatalkMost likely it's this.