loss of throttle response
 

I'm having an odd issue. After driving for about 5 minutes I lose throttle response at around 3000 rpm and as I continue driving it gets worse and I lose throttle response at lower rpms. When I press the pedal it wont die but it will hesitate and bog down. This happens without regard to temperature and will happen under load or in park. If I turn the engine off, and immediately start it back up it will run and drive fine and the issue will repeat after 5 minutes or so of driving.

I think its a sensor of some kind because its not happening all the time, it will run fine on start up and is responsive for a few minutes... but it consistently follows this pattern.

I checked the TPS with a multimeter and I think I can rule out the TPS. The blue wire has a responsive voltage increase as I open the throttle plates, even as the engine stumbles.

I'm not getting a SES light at any time.

I haven't checked fuel pressure for that reason but I've had to put a new pump and filter in recently and I don't think I'm having a fueling issue.

Any ideas?

Re: loss of throttle response
 

First place I'd look is at fuel pressure; eliminate that before searching further. In this day and age, 'new' parts aren't always trustworthy.

Re: loss of throttle response
 

your problem could also be the voltage supply to the fuel pump. sounds like a fuelling issue to me.

Re: loss of throttle response
 

WHAT VEHICLE? What engine?

As said, fuel pressure is suspect.

I would connect a scan tool and look at the data stream for clues.

Re: loss of throttle response
 

Thanks for the input everyone, I think I found the probem. its a 92 camaro with L03

13.7v at fuel pump

11.5psi idling... after I drove it and it lost power i parked it.. check fuel pressure again and it was inconsistent...opened the throttle plates and fuel pressure dropped to 0.

Fuel lines look to be in good condition...new fuel filter, and pump was replaced recently with a TPI pump.

I think the fuel pump is failing to provide under load. It probably is a defective unit. Im going to warranty it out and swap a new pump in. Ill update tomorrow on that.

I don't have the tool or any knowledge of that. When I get a SES light i use a paper clip and count the flashes. I'm not familiar with what your talking about but I'd like to know what I could do with a scan tool when I don't have an SES light. Could you point me to some information about that?

Re: loss of throttle response
 

Ideally, you'd be checking voltage and pressure while under load. An intermittent electrical connection could give you occasional "0" fuel pressure.

Most fuel pressure gauges have a push-button valve that bleeds fuel into a small plastic tube. Route the plastic tube into a drain pan, check pressure with the engine running and the button pushed so that fuel is flowing into the drain pan. That simulates high-volume flow through the injectors with the engine at idle.

Before I replaced the pump, I'd re-connect that fuel pressure gauge as above, and check voltage near the pump while doing the pressure test.



I'll direct you to another forum, where I made an extensive couple of posts regarding the use of a proper scan tool on OBD-1 vehicles, complete with photos.

Bear in mind that there's more than one brand of scan tool that can do this sort of work, and each brand has several models of varying ages and capacities. MY tool is ancient, but professional-grade. I'd rather have an old Pro-grade tool than a brand-new consumer/DIY grade tool. There was a time when "my"model of scan tool were all over eBay, at advantageous prices. It's so old that the newer models (but still obsolete for Pro use) in the Solus line are more popular now.

http://www.automotiveforums.com/vbul....php?t=1146067
Particularly posts 14 and 15.

Re: loss of throttle response
 

I don't have that style fuel gauge but I did a similar test. I drove the car until it hesitated then parked it. put it in park and put a brick on the gas pedal and it was hesitating and choking.. checked the voltage at the pump and it was a consistent 13.2-13.5volts. I warrantied out the pump and swapped a new pump in. it has made no difference at all, the symptoms are the same as before. fuel filter isnt clogged.
I'm stumped... I have no idea whats going on at this point

Re: loss of throttle response
 

Just a shot in the dark but have you checked for clogged lines after the filter, pin holes in lines, are both injectors spraying as they should while experiencing the "hesitating and choking", does the RPM gauge spazz out under this condition? The actual Fuel Pressure while experiencing the trouble will help narrow down your issue if you believe it to be fuel system related or rule it out.

Re: loss of throttle response
 

whats the best way to check for clogged lines or pin holes in the lines? RPM gauge seems accurate when the engine bogs it is consistent with that. It seems the injectors still spray when the engine bogs and fuel pressure drops off so much, but the pattern is really narrow. Could this maybe be a issue with the regulator?

Any help is really appreciated like I said I'm stumped at this point.

https://www.youtube.com/watch?v=Rk_c...ature=youtu.be
keep in mind if i shut the engine off, and immediately restart it, it will run fine until i drive for 3-4 minutes. then the same symptoms re-appear and persist

Re: loss of throttle response
 

I will speak on two observations

1. At 3 seconds into the vid you "blip the throttle" and as I was reading the shaky gauge... you dropped to nearly 0-2psi *IF* I was seeing it correctly. If so... crisis.
2. It was either the low fuel psi/volume or the passenger side injector was spraying far stronger than the driver side, could've been camera angle.

Onto my question(s)... Have you checked the entire length of fuel lines for visible leaks, actually felt around for wet spots or damaged lines? Have you ever had an SES light on, Code 44? You also mentioned your FPR, idk that it would even be suspect, your gauge is reading FP before it gets to the FPR...

Re: loss of throttle response
 

1. Did you check voltage on the ground side, too?

2. Connect the scan tool. Look at the data stream especially when the engine is acting up.

Re: loss of throttle response
 

Yes, your seeing it correctly it was barely above 0 psi.
Probably the camera angle there as they looked about even. I couldnt get a great angle of both injectors at the time.
Yes I cant see any damp spots or damaged lines under the undercarriage near the fuel filter or anywhere else.
No I haven't seen any SES at all

Re: loss of throttle response
 

Using the body as a ground with the positive lead on the ground wire of the fuel pump I'm getting a consistent .20v with it idling

Would a rental scan tool from o'reillys or autozone work? What would I be looking for? I read your posts about the scan tool earlier but I still don't know much about them because I have no experience with one. I'm trying to limit driving it because of whats going on.
https://cimg4.ibsrv.net/gimg/www.thi...7b5cd6e350.jpg
is the valve that my index finger on what captures gases and sends them to the charcoal canister?
I'm beginning to worry if i ran the fuel return and charcoal canister hoses backwards. I have the fuel return line running into this pipe
https://cimg9.ibsrv.net/gimg/www.thi...f32f2bf810.jpg
it dumps off near the fuel pump inlet

Re: loss of throttle response
 

I ran another test today. Got code 44 (Lean exhaust) this time. drove the car around the neighborhood and parked; fuel pressure was inconsistent at idle as usual, dropped off further once I rev it as usual; I plugged the return line and fuel pressure shot up and maxed out the fuel pressure gauge. revved the engine to about 4000ish rpms and fuel psi stayed maxed out the entire time with the return line plugged. unplugged the return line and fuel pressure was jumping around at 7-10psi. revved the engine and fuel psi immediately dropped off and the engine bogged down. repeated this test again with the same results.

I had a spare FPR laying around so I compared it to the one on the car and swapped it in.
This seemed like it just upped my fuel pressure I was running about 14psi with it and I had the same issues during the test drive but it seemed to take a higher engine speed under load before it couldnt fuel it properly. I checked fuel pressure after it was a pretty consitent 14psi at idle and it dropped off when revved, but it seemed like it had to rev to a higher engine speed before fuel pressure dropped enough for it to hesitate.

The other FPR seems like a bit of a band-aid for now because it doesnt bog down as easily.

I probably wont get the chance to work on this again until Tuesday; I'm planning to :
1. rent a scan tool
2. take apart FPR and clean it
3. get a dial caliper and measure the lines to make sure that I didn't improperly route them by chance. I've read on here the return line is 5/16 od. and the line to the charcoal canister is 1/4 od.

if anyone can shine some light on the white valve (in the first picture of my last post) on the fuel sending unit I would appreciate that.
and thanks again for everyone who responded, this has really been beating me up over the past few days.
https://cimg0.ibsrv.net/gimg/www.thi...130cabc528.jpg
left-spare FPR i swapped on right-original FPR
https://cimg7.ibsrv.net/gimg/www.thi...3d8f98d7a9.jpg
fuel tank vent valve is broken off but I dont think its related. I plugged it and it didnt change anything

Re: loss of throttle response
 

I thought if you plugged the return line and the FP shoots up then you'd be looking at some blockage, I not sure if it's the feed or return side tho... Btw PLEASE remember your testing the FP before it even gets to the FPR so swapping them wouldn't have made a difference. If I were you, I'd be focusing on the feed side first then the the return side. The scan tool is going to be SUPER valuable however you're not going in blind, we know you're running lean w/ Code 44 as I asked about before, we know your FP is far below where it needs to be under load for drivability so knowing things a scan tool will tell you like your BLM or INT, O2 Voltage, MAP Voltage, etc will be useless if your FP gauge says 0-2psi of fuel pressure. My :2cents:

Re: loss of throttle response
 

14 psi is ideal, did you reuse the FPR diaphragm off the original FPR? Perhaps it is failing. if you blip the throttle to WOT from idle while watching the fuel pressure the needle should bearly moving. 1/2 psi at MOST, ideally not move at all. fuel pump or regulator suspect. i still wouldn't rule out electrical. i would do a voltage drop across the relay and oil pressure contacts, should be a few milivolts. anything more than 500mV is too much.

Re: loss of throttle response
 

https://cimg8.ibsrv.net/gimg/www.thi...aaa5e0600e.jpg
I had to take a break for finals but I'm back and I solved the problem. I wanted to bring this thread back just to show this very unlikely problem.

It was the fuel pump strainer. I put a new strainer on and I'm no longer having fuel pressure issues... My theory is that the loose frayed end you can see in the pic was obstructing flow into the pump...

This strainer came with a sending unit I bought from 1aauto. The rest of the sending unit seems to be decent quality. My fuel gauge is relatively accurate which is the reason i changed the unit in the first place.
https://www.ebay.com/itm/Fuel-Gas-Ta...-/350921260430
if anybody uses this be aware the strainer is poorly designed.

Re: loss of throttle response
 

Good job figuring that out!