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  99 l67 swap sputtering under wot and over 3800 rpms

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99 l67 swap sputtering under wot and over 3800 rpms by jhobbins
Started on: 10-07-2019 06:31 PM
Replies: 20 (179 views)
Last post by: 2002z28ssconv on 10-20-2019 11:33 PM
jhobbins
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Report this Post10-07-2019 06:31 PM Click Here to See the Profile for jhobbinsSend a Private Message to jhobbinsEdit/Delete MessageReply w/QuoteDirect Link to This Post

Hey guys, I'm having an issue where if I either ease into the throttle up to 3000 rpms, it breaks up when it gets there. I have 40psi of fuel pressure at idle and it maintains that pressure even when it's breaking up. If I go wot the engine also breaks up. According to my torque pro app, the commanded spark advance drops way down when it starts sputtering, so it seems like the computer is pulling the timing. Does this sound like an ignition issue, or a wiring issue? I've got fresh 93 octane fuel in it.

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olejoedad
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Report this Post10-07-2019 10:14 PM Click Here to See the Profile for olejoedadClick Here to Email olejoedadSend a Private Message to olejoedadEdit/Delete MessageReply w/QuoteDirect Link to This Post

Fuel pressure is low to start with....

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jhobbins
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Report this Post10-08-2019 12:23 PM Click Here to See the Profile for jhobbinsSend a Private Message to jhobbinsEdit/Delete MessageReply w/QuoteDirect Link to This Post

Oh really? I'm more familiar with SBC's so I thought that was a good pressure reading. I'll swap the fuel filter and see if that helps any

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olejoedad
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Report this Post10-08-2019 01:24 PM Click Here to See the Profile for olejoedadClick Here to Email olejoedadSend a Private Message to olejoedadEdit/Delete MessageReply w/QuoteDirect Link to This Post

You need 50+ lbs and rising higher under boost.

What fuel pump are you using?

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OntarioKev
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Report this Post10-08-2019 09:57 PM Click Here to See the Profile for OntarioKevSend a Private Message to OntarioKevEdit/Delete MessageReply w/QuoteDirect Link to This Post

Check fuel pressure at idle with the vacuum line to the regulator disconnected.

With the boost referenced fuel regulator under vacuum the pressure is lower and it increases with boost. Please let us know what the pressure is when running with the vacuum line disconnected.

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jhobbins
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Report this Post10-09-2019 09:52 AM Click Here to See the Profile for jhobbinsSend a Private Message to jhobbinsEdit/Delete MessageReply w/QuoteDirect Link to This Post

I'm not 100% what pump is in there, i bought the car with the swap already in progress. The PO said it was an SUV fuel pump that was recommended on the forums, but he couldn't remember which one. I'll test the fuel pressure again when I get home today thanks

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jhobbins
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Report this Post10-09-2019 05:01 PM Click Here to See the Profile for jhobbinsSend a Private Message to jhobbinsEdit/Delete MessageReply w/QuoteDirect Link to This Post

Key on, vacuum line unhooked, 41psi. Idleing 40psi.

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BadNewsBrendan
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Report this Post10-09-2019 05:20 PM Click Here to See the Profile for BadNewsBrendanSend a Private Message to BadNewsBrendanEdit/Delete MessageReply w/QuoteDirect Link to This Post

This link says GM service manual says 45-55: https://www.fastfieros.com/...uel_pressure_L67.htm

Also gives some procedures for testing fuel system.

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jhobbins
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Report this Post10-09-2019 05:50 PM Click Here to See the Profile for jhobbinsSend a Private Message to jhobbinsEdit/Delete MessageReply w/QuoteDirect Link to This Post

Scratch that, I'm an idiot. I unplugged the wrong hose. 40 key on engine off, 50 engine idling with the fpr vacuum line unhooked. Probably a bad fpr then?

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Dennis LaGrua
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Report this Post10-09-2019 05:54 PM Click Here to See the Profile for Dennis LaGruaClick Here to Email Dennis LaGruaSend a Private Message to Dennis LaGruaEdit/Delete MessageReply w/QuoteDirect Link to This Post

If your fuel pressure is up to spec and the exhaust unrestricted then you need to take the next step. I realize that many DIY mechanics don't like hearing this but a full diagnostic scan of the PCM will pinpoint the trouble. The symptoms you describe can be one of any number of things. Failing to do a scan is working in the blind. .

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jhobbins
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Report this Post10-09-2019 06:08 PM Click Here to See the Profile for jhobbinsSend a Private Message to jhobbinsEdit/Delete MessageReply w/QuoteDirect Link to This Post

 
quote
Originally posted by Dennis LaGrua:

If your fuel pressure is up to spec and the exhaust unrestricted then you need to take the next step. I realize that many DIY mechanics don't like hearing this but a full diagnostic scan of the PCM will pinpoint the trouble. The symptoms you describe can be one of any number of things. Failing to do a scan is working in the blind. .



Correct me If I'm wrong, but the fuel pressure at idle going up to 50 with the fuel pressure regulator unhooked would mean that it is something related to that regulator.

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OntarioKev
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Report this Post10-09-2019 07:17 PM Click Here to See the Profile for OntarioKevSend a Private Message to OntarioKevEdit/Delete MessageReply w/QuoteDirect Link to This Post

No, that is the expected behavior, the fuel pressure rises with boost. It should be higher at atmosphere (which is with the line disconnected).

Are you able to monitor fuel pressure while you are experiencing the issue? If the fuel pump is not up to the ask, or on its way it could provide the correct fueling during idle but drop under load.

But if you are really having fueling issues it can be damaging to the engine to go under load. If you do a quick check and your fuel pressure is good there are other things to look at.

I personally always have a wideband O2 sensor installed in my modded cars. With that you could see if your AFRs are too lean or too rich when the issue is happening, and that would help with the next steps.

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jhobbins
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Report this Post10-09-2019 07:49 PM Click Here to See the Profile for jhobbinsSend a Private Message to jhobbinsEdit/Delete MessageReply w/QuoteDirect Link to This Post

The fuel pressure holds at 40, even when I hit 3000 rpms and it starts misfiring

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olejoedad
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Report this Post10-09-2019 08:02 PM Click Here to See the Profile for olejoedadClick Here to Email olejoedadSend a Private Message to olejoedadEdit/Delete MessageReply w/QuoteDirect Link to This Post

Why would you unhook the vacuum line when checking fuel pressure?

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OntarioKev
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Report this Post10-09-2019 09:49 PM Click Here to See the Profile for OntarioKevSend a Private Message to OntarioKevEdit/Delete MessageReply w/QuoteDirect Link to This Post

Verify the rising rate function of the Fuel pressure regulator. If you look at the testing procedure you will find this.

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jhobbins
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Report this Post10-11-2019 11:09 AM Click Here to See the Profile for jhobbinsSend a Private Message to jhobbinsEdit/Delete MessageReply w/QuoteDirect Link to This Post

I was able to verify that as boost increases, so does fuel pressure. I had 50 psi at 3000 rpms and it was still climbing when the misfire started. I'm going to begin diagnosing the ignition components, I believe that may be where my problem is

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olejoedad
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Report this Post10-11-2019 06:03 PM Click Here to See the Profile for olejoedadClick Here to Email olejoedadSend a Private Message to olejoedadEdit/Delete MessageReply w/QuoteDirect Link to This Post

Do you have data logging/scanning capabilities?
What is the MAF sensor telling you?
Tell us or post a picture of your intake air system.

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jhobbins
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Report this Post10-11-2019 07:40 PM Click Here to See the Profile for jhobbinsSend a Private Message to jhobbinsEdit/Delete MessageReply w/QuoteDirect Link to This Post

I currently only have the torque pro app for scanning, I just ordered hp tuners though. I also don't see how to upload an image on here.

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Buck531
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Report this Post10-11-2019 10:33 PM Click Here to See the Profile for Buck531Click Here to Email Buck531Send a Private Message to Buck531Edit/Delete MessageReply w/QuoteDirect Link to This Post

It may not even be fuel related. It might be a spark issue.

So many variables here.

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Report this Post10-18-2019 03:22 PM Click Here to See the Profile for Jay-IDClick Here to Email Jay-IDSend a Private Message to Jay-IDEdit/Delete MessageReply w/QuoteDirect Link to This Post

I saw a similar problem. Make sure you've got the speedometer (VSS) connected and feeding the L67 PCM. It can cut fuel.

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2002z28ssconv
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Report this Post10-20-2019 11:33 PM Click Here to See the Profile for 2002z28ssconvClick Here to visit 2002z28ssconv's HomePageSend a Private Message to 2002z28ssconvEdit/Delete MessageReply w/QuoteDirect Link to This Post

Sounds familiar with what I used to get so here's what my issue was. But to be clear, diagnosis should always find a problem prior to random part replacement.

If your coils are relocated and no longer on the engine, make sure they have a dedicated ground running to the ICM wherever they're mounted. I relocated mine to the firewall and it would puke all over itself as soon as I got above about 1 pound of boost. I was also burning occasional spark plug wires, like they were fuses. Running a new ground resolved everything.

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