6.0 wont rev past 1200rpm

[Painter D]

Took my first spin in my LS swapped 58 swb and the motor is unresponsive after 1200 rpm. It doesnt die it just acts like its hitting a rev limiter. Any thoughts what is causing this issue?


Its a 2003 lq9 6.0 with a PSI stand alone harness
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[BR3W CITY]

Is it throwing a fault code, any other symptoms etc?

Is it dbw?

How was it tuned?

[Painter D]

Originally Posted by BR3W CITY

Is it throwing a fault code, any other symptoms etc?

Is it dbw?

How was it tuned?

Not sure if its throwing codes or not I dont have a scanner, I'm going to try to get my hands on one today. It's NOT throwing a cel, and there are no other symptoms.

Yes, its a dbw


It's a mail order tune, not sure how it was tuned.
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[Clyde65]

sounds like limp mode to me.

[ls1nova71]

Do you have a fuel pressure gauge you can put on it? Low fuel pressure will do what you are saying....

[Painter D]

Originally Posted by ls1nova71

Do you have a fuel pressure gauge you can put on it? Low fuel pressure will do what you are saying....

No, but I can get one.

If the fuel pressure was to low , wouldnt that affect the idle, as well as the rpms below 1200?
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[ls1nova71]

Originally Posted by Painter D

If the fuel pressure was to low , wouldnt that affect the idle, as well as the rpms below 1200?
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No, not necessarily. I had the hose between the pump and sender get a hole blown through it a while back and the car would start and idle fine, but when you went to take off it would fall on it's face, it was running on 15psi!!!

[BR3W CITY]

Does it rev in nuetral, or is the 1200rpm limit at all times?

Could be a DBW/TAC problem, but those usually cut off ALL response at the pedal , not just above a certain point.

[storm9c1]

I couldn't imagine doing a LS swap without a code scanner (and a real-time parameter monitor). It is the first tool to use when strange things like this start to happen. Get one. You WILL need it.........

[Painter D]

Originally Posted by BR3W CITY

Does it rev in nuetral, or is the 1200rpm limit at all times?

Could be a DBW/TAC problem, but those usually cut off ALL response at the pedal , not just above a certain point.

It wont rev any higher no matter what gear its in ,Park, Neutral,or Drive it does the sme thing all the time.


I dont have a tach hooked up Im guessing on the 1200 rpm thing , but its definitely not far off from that.
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[Painter D]

Originally Posted by storm9c1

I couldn't imagine doing a LS swap without a code scanner (and a real-time parameter monitor). It is the first tool to use when strange things like this start to happen. Get one. You WILL need it.........

Will do.

Can you recommend one to get?
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[BR3W CITY]

At minimum the $15 thing from Harbor Frieght will tell you whats the basic CEL's are.

I bought a ScanGuage to use in my trucks dash, it reads most codes and as a bonus it displays the engine parameters as a functional gauge I use while driving.

[Mikec10]

You could use the torque app and check codes on your phone a long with parameter monitoring, all you need is a 15$ bluetooth obd2 connector

[Painter D]

Ok, good and bad news.

Its not throwing any codes and the dbw stuff is operating correctly. I was able to rev it pretty high as long as I push the gas pedal slow, and I mean extremely slow. When I do this though it is sputtering and running extremely rough. After about 4000 rpm it falls on its face, if I can even get it to rev that high without falling on its face. If I push the gas pedal fast at all ,forget about it. All this without throwing a single code. Im stumped.

Could it be as simple as bad spark plugs, the motor sat for about a year?
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[truckdude239]

Injectors are probably stopped up
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[BR3W CITY]

Clogged injectors, I swear we just had another member have an issue and after new o-rings and soaking the injectors, his truck ran fine.

Could also be the fuel pump is dying, there is a restriction in the line, the filter is effed, your not calling for (or getting) full fuel pressure. I say all fuel stuff because bad plugs and coils trigger Misfire Detection codes pretty easily unless the counter has been set really really high.

[Painter D]

How do I unclog the injectors?
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[Painter D]

The fuel pump and filter and tank are brand new.
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[Clyde65]

I believe you have to soak the injectors in sea foam and then you need to figure a way to have them fire outside of the truck to get the tar and stuff out of it. I knwo I have read it before but I cant remember it all.

[Painter D]

I think I got it figured out, the fuel pump relay isnt working properly.
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[68GMCCustom]

besides soaking the injectors.....you can fire an injector with a 9v battery. Hook a spray can cleaner to the fuel inlet side and fuel the injector with a 9v battery connectors leads and some alligator clips.

[faribran]

i just went thru cleaning all my injectors.... pretty easy.... and i am glad i did it..

i used PB blaster in a syringe, a small rubber hose to connect the syringe with the injector. short pigtail from a spare harness, i used a regular full size car battery.. i just touched the wire to post and pulled it away to make the injector fire....
i hope this helps..

[smoky02]

look at that my dad is educated on all the fuel injection stuff now...get it Faribran...you know more than me...

[faribran]

Naah bud.. i learn every day from you..

[Painter D]

It was the fuel pump relay , it wasnt sending constant power to the pump, it was sending an intermittent signal. Which was dropping the fuel pressure down to 10psi when I pushed the gas pedal. The interesting part is that the motor was running on 35psi, didnt figure it would do that.
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