Our firebird fuel line was too close to exhaust,, vapor lock,, on your car, could be same thing... or wrong/weak valve springs

Also, we had a truck that was doing something similar,, had a cheap pump on it,, the pump motor would get hot and would not turn fast enough, truck would run fine after it cooled down,,

fuel starvation to the pump will cause it to get hot and turn slow also,, like maybe the inlet is stopping up,, also if the tank vent is stopped up it will pull a vacuum and not get fuel, and or the gas tank cap vent,, about as long as it takes the car to warm up is about as long as it would take for it to pull a vacuum and quit pulling enough fuel to run fast.... our firebird does this if the vent is plugged

 

Could there be loose particules of rust in the tank that are all collecting on the sock/pre filter starving the pump for fuel, thus dropping the pressure?

that would explain why it has pressure cold right? and why it disappears after ten minutes.....:shrug:

 

Sumbitch. That totally slipped my mind. While not a common thing it can happen.

That would qualify as an overlooked something. Easy test is keep the bloody gas cap off while running the engine to the point where you typically run into problems.

One other thing, is it possible to get some pics of your vacuum routing on the pass side.

 

I agree with SmithTC. Check for the fuel line to close to the exhaust. Also the vent for the fuel tank. I have seen both happen. Allen

 

im going to tell you a short story

guy has 1990 mustang.

shop puts in a fuel pump. car craps out
another shop puts in a fuel pump. car craps out.

another shop puts an intertia switch in

geuss what car craps out.

next shop replace the the fuel pump relay and the EFI relay and rewires the whole damn thing from the tank to the back of the car geuss what. car craps out.

now how did i find this ??

USE A LOW AMPS PROBE !!!!!! your fuel pump actuall draws the largest amount of current at idle. thats becuase its working super hard having to bypass directly from the regulator to the tank.the largest amount of fuel goes back to the tank KOEI KOEO

so if the pump has a good electrical pattern at idle with the relay jumped and the engine off i can guarntee you its not a pump. also pinch the return line off see if the pump craps out electrically at higher fluid pressures. fuel pressure does go up around 5-6 psi at WOT. vs engine idling

now with that said.

are you using the correct sock on the pump ???? cavitation can cuase similar problems

check the actuall potted wiring going into the tank sneding unit. i have seen ( the above mustang) high current high vloume pumps will load the wiring up and the potting will break loose the wiring will break and the sending unit was the real culprit.

but since its a problem you only have at 1/2 to WOT. id think you most liekly have a restricted fuel filter or something. sounds like a pinched line etc etc etc. if you dont have volume then you cant have pressure.

an electrically bad pump would have striaght up quite working. aso i hate to say this but have you checked the connectors comming out of the rear sheet metal ??? i know it is a pita to remove but you may want to yank the rear seat pull up the carpet and inspect that connector inside and out. at least that part can be done without droppping the tank.

id still check for a pinched fuel line. espcially if someone has put you car on a hoist right before the problem started. youd be surprised how many pinched fuel lines ive seen in my life due to negligent lifting.

 

i know you said you changed it, but something else to check is the fuel filter, i have seen more than one GM vehicle where the filter got put on backwards & was missed by more than 1 shop. put on the wrong way they would work fine, for a time & then start working like a check valve & cause problems like what you are describing.

the only one i cut apart the filter media had collapsed in it. it was designed so when installed in the right direction the fuel flowed in into the center of the media to the outside of it.
i think what happens when the filter is on backwards is when you are on the gas harder the flow increases through the filter which is what collapses the media which causes reduced flow, the more it collapses the more the flow is reduced which causes it to collapse even more. turn the car off for a few minutes & the filter returns to a somewhat normal shape & will allow fuel to flow normaly through it again. the longer the car is off, the longer it takes for the problem to come back.

what funstick said about using an amp probe would show this as an increased current draw.

 

He doesn't need to datalog the car. If he has 10 psi, the that is the problem. If he by passes the the fuel pump relay w/a jumper wire, the that eliminates
*the ECM completely
*the relay
*the oil presure switch

If he is loosing presure with 12.0+ volts, then he either has
*a bad pump,
*a restriction (Sock, filter, kinked line, etc)
*a leak (the hose between the pump and the sending unit?)

I think the fuel filter (backwards) and the tank vacuum are both good suugestions and definitely worth checking.

 

Tom, why pick one of my older posts in the thread to quote? It really wasn't needed for what you posted, however, it does illustrate a good point here in that I still am unsure if the pressure drop corrolates exactly to the switch to closed loop.

You could also have easily just suggested putting 12v to the G terminal of the aldl immediately after a stall to see if the static pressure goes past 10 psi. I still don't see how my earlier post puts your into context or anything. :shrug:

 

Because it looked like fun!

 

Because IMO, there was a series of posts in this thread following yours that mentioned datalogging and it seemed like it stemmed from your post. I think there is no need for data logging until you have the correct fuel presure from the basic parts. K.I.S. That's all...Didn't mean to offend.

Putting 12v to the ALDL tells the ECM to engage the fuel pump relay doesn't it? I would suggest by-passing the relay first w/a jumper wire, to verify that the fuel pump and lines etc. -the basic parts- are working correctly.

 

IT was very difficult to read this thread.

Do you have a fuel pressure gauge on the car right now? If not, can you please install one that you can see from the drivers seat? I"m willing to help you solve this, including you coming into thirdgen chat and me walking you through this. But you need to follow what I say exactly, since the car is not infront of me.

First thing i'd like, is for you to have both a fuel pressure gauge, and your scanner connected to the vehicle.

When the car enters closed loop, i'd like you to record the blm and int at idle. How quickly the o2 crosses, and a rough idea of the o2mv, and note your
fuel pressure.

Start driving.. Do what you do to make the car "break down". While its breaking up or down orwhatever you call it, have a co-pilot record the fuel pressure, blm, int, o2mv, spark advance, and knock retard.

Come back to me with this information.

This is the first thing you should have done. Log engine data, and record fuel pressure.

-- Joe

 

Here are the numbers I sent to Ed Wright when I thought it was the chip that was causing the problem.

RPM-- 1900 3200 4000

Block Learn-- 122 128 128

O2-- 51 23 4

TPS-- 1.32 2.96 4.32

Temp-- 173 173 175

MAF-- 47 131 168

I have since changed the MAF and TPS, but the numbers should still be similar due to the problem. When You baby the throttle, it maintains enough fuel pressure to drive. I had it out on Christmas Eve and it stalled twice on my way to a party. When I left two hours later, I was able to leave two long strips on the main road. When I made the turn onto my street, it stalled and again in the driveway.

 

I took my headache to another shop. The owner looked at my car an spent some time on it. It all boils down to a bad fuel pressure regulator and one bad injector. So I rodered the TPIS regulator and will exchange the injectors for another set. I should have parts by Monday and hopefully have the car back on Wed. or Thurs.