5.3 WOT Issues. Tried many things. Can't Figure it out!

[Boulky1212]

Really need some help. Been trying many things to fix a WOT issue on my truck and nothing seems to help. Getting very frustrating.

Truck is an 86 GMC swb. 5.3/4L60E. Engine has headers. Trans has corvette servo. That's it.

I can drive the truck all day long no issues. But whenever I give it full throttle it will be all good and pulling up until about 4-5,000 rpm, then all the power just cuts out and trans dosen't shift. Also the problem is intermittent. Sometimes it will do full throttle pulls great and shift great, but most time not. I've also noticed the problem may be due to heat. The times I can get it to go WOT and shift good, I've only been driving for 5-10 minutes. But every single time I take a 30 minute drive down to the drag strip and try to get a run in, the problem happens.

So far I've tried many things on hptuners(setting things back to stock, changing shift points), new tps, new fuel pressure regulator, put fuel pressure gauge on the rail(getting 58psi @ idle), new spark plugs and wires, tested for vacuum leaks.

I'm having a hard time thinking of what else it could be.

Only thing I'm thinking is maybe the fuel pump gets hot and weak after driving for a while. It is an in-tank Spectra Sp1115 and many LS swap guys use them in these trucks up to 500hp.

I've attached my tune and a data log of when the problem happens. (first spike in the graph is burnout, second one is the run/problem happening). I'd really appreciate if someone could look at these and give me some advice.

Thanks

[castorjames]

have you verified your fuel pressure at WOT? how is your intank pump setup?

[Boulky1212]

Thanks for replying castorjames.

I went out now to check this. Before I did, I adjusted the fuel pressure regulator. Was told 58 psi @ idle is incorrect, and should be 58 psi with regulator vacuum line unplugged. So I set it to that. Now I'm at 51 psi @ idle with vacuum line hooked up. And when I snap the throttle Wide Open it only goes up to 60 psi. Is this normal? I did this just sitting in park. Might it show different with a load on it?

And I forgot to mention. The 5.3 is a 2000 model Drive by cable with Return style fuel rails.

In tank pump setup is pretty normal and tested to be good by a lot of people Ls swapping these 73-87's. New 87(fuel Injection) tank, new 87 sending unit, new spectra sp1115 pump, new strainer, FI rubber fuel hoses from tank to fuel filter, new fuel filter, then factory fuel lines from donor truck from fuel filter to fuel rails.

[kevin87turbot]

There's something going on with your MAP sensor at WOT. It appears to be dropping signal and drops from 94 kPa at 4000 rpm all the way down to 30 kPa at 5000 rpm. It's likely a restriction in your inlet pipe or a coupler that collapsing under full load. If that's not it, then check the MAP sensor mounting and connection carefully.

[Boulky1212]

Thank you very much for taking a look kevin87turbot.

I will definitely look into this and report back.

Thanks

[kevin87turbot]

Thank you very much for taking a look kevin87turbot.

I will definitely look into this and report back.

Thanks

Good deal. I ran into this same thing a few months ago on a friend's Tahoe. The rubber bellows was collapsing once it got warm and pliable.
I suspect you have the same thing going on.

[Boulky1212]

Good deal. I ran into this same thing a few months ago on a friend's Tahoe. The rubber bellows was collapsing once it got warm and pliable.
I suspect you have the same thing going on.

I didn't understand what you meant at first but now I see you're talking about the air intake rubber coupler pieces. On my setup, it would definitely have to be the 90 degree coming out the throttle body. I felt it and man it does actually feel pretty flimsy. Probably very flimsy after driving for 30 min. It looks like a cheapy one and old, so gonna go ahead and replace it. From the way the problem feels when it happens, it makes sense that this thing was probably just collapsing.



And on the map sensor. I inspected the wires, look fine. I figure power and ground were okay since it does act normal for the most part. I wanted to do vacuum test and get a reading off the signal wire. But found out parts stores don't rent that pump. They only sell it and it was 60 bucks. Same price on amazon. They have a cheapy one for 20 but ehh. The map sensor was pretty dirty too. That might've been causing an issue. I think I'll just clean it up good, spray some carb cleaner down that hole in the intake, and hope the sensor is still good.



I have a good feeling about the rubber coupler piece tho. I'll let yall know.

Thanks kevin87turbot!

[kevin87turbot]

Did you ever get your issue resolved?