Doggy At Wot

[MARKO]

Hey guys I have a 86 GN and have a bit of a issue. It pulls good
if you're at 1/2 throttle or 3/4. As soon as you try WOT it seems
like it gets doggy or doesn't pull as hard after 3500 rpm. If I were
to slightly let off and only have it at 3/4 throttle instead of WOT
it feels like it picks up better. Kind of confused. The car has
a rebuilt motor with 800 miles on it. Green stripe injectors, 260H
comp cam, precision turbo, adj wastegate, adj fuel reg. 3" downpipe, 2 1/2" exhaust, red's 93 chip, rblt trans w/2500 stall.
Any info would be helpful. I'm new to this and am used to carbed
V-8's. Thx for your help

 

[mar86gn]

Hi i dont see anything about an upgraded fuel pump. You need to upgrade this asap. It sounds like its leaning out.

 

[Haynesie]

I had a problem somewhat like this
It was after i disconnected the BOV vacum lines becuase they were unnecsarry, if you have a BOV make sure its connected, i guess you really dont need one, but that is something that cuased a bit of trouble in my car so just a thought.

 

[murphster]

What Octane are you running? With my GN I had a similar problem and it turned out I was getting knock at WOT. The car would retard the timing and get doggy. I put some Xylene in and that cured the problem.

Leaning out would probably give similar results, so its hard to tell without a scan tool, but its a start.

You could also check the throttle position sensor (TPS). If its not adjusted right or going bad, WOT could be affected. You would need a scan tool or a digital Voltmeter.

Since you don't have any stuttering or anything, you could maybe rule out ignition, MAF, fuel filter, etc. These are more likely to give jerks, pops, hesistation, etc.

Many people mention old valve springs hurt top end, but I'm not sure if it would produce the symptoms you are talking about.

Exhaust leaks on the crossover pipe and intercooler hose leaks would limit the boost build up so I assume your boost is building correctly.

Just some ideas.

 

[MARKO]

I've got a upgraded fuel 255lph and I run 94 octane at 15psi. Also not sure what BOV is?? Have Scanmaster 2.1 but am not sure what to look for on it. I try to watch o2 reading and it seems
to be in the 700's. I will have to double check. Do you guys know
what TPS reading is supposed to be at WOT? I think mine is in
the 4's somewhere.

 

[MARKO]

I just went out to try driving it again. I noticed on the scanmaster
that if I had 1/2 to 3/4 throttle slowly building boost the o2 readings were anywhere from 720-820. As soon as I floor it
the readings drop to like 023. It's leaning out for some reason?
I'm going to hook up fuel pressure gauge to it tommorow
and see. Pressure at idle is 41psi, is that to low? Don't
really know what else to look for? Thx for help

 

[XLR8]

A good starting point for FP is 42# - 44# with the vacume line to the FP regulator disconnected. It will drop 5# - 6# after the vac line is hooked back up. If you can, tape the FP gauge to the windshild and watch it under boost. It should rise pound for pound with the boost, i.e. if FP starts at 42# line-off, at 15# of boost the FP should be 57#.
Other thoughts. While watching the Scanmaster, do you notice any Knock Retard? What is the TPS at WOT? It should be 4.50 or greater. You can check that with the engine off.

 

[MARKO]

I'll have to have a look at my TPS at WOT. Wondering about
the Scanmaster and the Knock retard. I'm new to all this
so I've slowly been figuring things out. Is the knock retard
the figures beside the o2 readings? Also, if I take it out for
a drive and I'm not getting a spike in fuel pressure, is it
the regulator or could there be something else? Either way
I'll hook up the f/pressure gauge and see what happens.
Thx for all the info guys

 

[XLR8]

Yes the KR is the number next to the O2. You want 0. If there is knock retard, the computer is pulling timing and slowing you down. If fuel pressure does not increase with boost, it could be the regulator but first I would replace the fuel filter. Is your fuel pump hot wired?

 

[MARKO]

Yes the car came with the fuel pump hotwired i believe. It's got
an extra relay at the back. I change the fuel filter when I put
the motor in about 800 miles ago. Also did injection flush because
I had a problem with the car stalling after driving it and it
turned out my fuel pressure was dropping to 20psi whenever
it felt like it so I changed the pump and it all seems ok except for
this WOT problem.

 

[MARKO]

I took the beast for a rip at lunch here with a fuel pressure gauge
hooked up. At idle it was 49 with the vacuum line off and I set
it to 41. The car seemed to build fuel pressure up to about 47-49
roughly and then when at WOT it drops to 39 or so.
Probably regulator?

 

[azgn]

more likely the fuel pump or a voltage problem or a problem with the vac line going to the regulator

you can test all of the above with a mighty vac except the fuel pump

 

[MARKO]

I put a new 255lph fuel pump in a month ago because the old
used to drop pressure when you'd start driving it. The fuel
pump to my knowledge is hotwired. There is a relay in the
back and a wire goin to my alternator I think. I'm gonna have
to check. If that's the case how can I check the voltage to see
if it's droppin or if that is my problem? The vacuum line seems
to be alright, but I'll put another one on there.