Cutting Out At ~14 PSI Boost - Suspect Fuel Pump

[Chuck Leeper]

The "runs ok at 90% throttle" comment has me wondering: Is the TPS failing? Key on, engine off, slowly apply throttle to WOT. Watch the SM. TPS go smoothly to 4.5v?

 

[Boost231]

That line is pretty hard, so it's hard to pinch. So I capped it (screwed in a big bolt...very tight fit). I turned on the ignition/power to the pump, and it went to 52. I did it again a couple minutes later and it went to 53.

~But I just noticed something that might be important. When putting power to pump (ignition on), the instant the pump shut off, the fuel pressure dropped back down to almost 0 within a couple seconds. Is that normal?

I know, I'm concerned about low O2 MV's. I check the Scanmaster after every run. The lowest I've seen during these test runs is 789 (most are low 800s). Don't you think that's saying I'm not really anywhere near an engine damage danger zone?

The pump dropping to zero immediately is not normal.

I would cap that line and apply 12 volts to the jumper wire. You should get over 90 psi.

But since it's dropping to zero psi after the pump turns off its time to drop the tank.



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[bison]

If you suspect the fuel pump you need to flow test the fuel pump at the pressure you are looking to run. With base pressure at 52 and you want to run 20 at the manifold you would flow test at 72psi. Speculating about a fuel pump and not actually flow testing it is a waste of time. So it's time to get off the internet and start flow testing. You find out what your pump should flow at a given pressure/voltage and compare to what you actually have


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[Terbro]

Apply regulated pressure to the vac/pressure port of the fuel pressure regulator . Start at 10psi , turn on the pump with the prime wire with 0 air pressure , check base psi , apply 10psi & should go to base + 10 . Go on and increase air psi and FP should rise 1 for 1 up to at least 70 psi . No driving required . Sam

Yeah...it's above my capacity to do something like that. Don't have the equipment. I've r&r'ed a TR motor a decade ago, can r&r just about anything physically on a car, and so obviously have cranked a lot of wrenches. But when it comes to electronics or the more technical knowledge...it's above my head (which is why I'm on this board). I've got a tackle box of the most basic tools, a volt meter, $40 floor jack, jack stands - and that's the extent of it.

 

[Pronto]

Let me guess, Accufab adjustable fuel pressure regulator?

 

[Terbro]

Let me guess, Accufab adjustable fuel pressure regulator?

Can't say...came on the car when I bought it. Attached is a photo. Can anyone tell by this shot?

 

[No disintegrations]

Can't say...came on the car when I bought it. Attached is a photo. Can anyone tell by this shot?

Can you take a picture of the top of the coil pack, I have an idea.

 

[Boost231]

Not a accufab, that's a old school billet top stock base unit

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[Pronto]

The fpr may be not functioning correctly.

 

[Terbro]

If you suspect the fuel pump you need to flow test the fuel pump at the pressure you are looking to run. With base pressure at 52 and you want to run 20 at the manifold you would flow test at 72psi. Speculating about a fuel pump and not actually flow testing it is a waste of time. So it's time to get off the internet and start flow testing. You find out what your pump should flow at a given pressure/voltage and compare to what you actually have

Again, above my ability to do any flow testing myself.

Here's the scoop. My fuel tank doesn't look so hot. It's got a dent in it, and I've been thinking of replacing it anyway. So I could buy a new tank (suggestions welcome on a vendor), and either just do as I've done in the past - throw parts at the car until I've covered everything possible - n this case, just buy a new DW300 pump (I've found them online for ~$140), also replace the sending unit and tank, and do the wiring as well.

But I'm getting a feedback from different folks, which of course I appreciate, but not certain not which step to take next. Of course, I like the idea of a faulty FPR...easy, relatively inexpensive fix. Maybe I should replace that first to eliminate that possibility. With my limited resources and technical know-how, it's kind of looking like inspect, and then replace each possible suspect part until it's resolved.

 

[Terbro]

Can you take a picture of the top of the coil pack, I have an idea.

See attached.

I'm happy to do it, but I do like knowing what people are thinking before I go out and do things though. I was asked to pinch test the return line, not knowing what I'm looking for. Did that, and still don't know why. Helps us all learn when it's explained.

 

[Terbro]

Question: Are the DW300 FPs, known to be much louder than say a Walbro 340 or stock pump? The reason I ask is - last night, when I was doing the test with the return line capped off, the pump didn't sound especially loud. I've heard some loud fuel pumps in my day, and this one wasn't anything like that. It's not a pump that would ever be loud enough to hear if the motor was running. And my SS Pypes exhaust isn't that loud at all. Point being - just wondering again if I've actually got a DW300 pump.

I'm all for dropping the tank and replacing the pump, but maybe I'll inspect the fuel lines further for kinks, replace the FPR first?

And I've been told that there's no practical difference between a DW300 and 301, other than the outer housing - the internals are the same. Is this true?

 

[Boost231]

You didn't do a pinch test the correct way. You need to block off the return apply power to the jumper wire and see what it does. Should go over 90 imop


If that checks out jump the wire and start applying pressure to the top of the regulator and see what the pressure does. I'm going to guess this is the issue.

A dent tank isn't the issue. Why buy another pump when a new one was just installed. You said you added a ground with no change and I don't belive this is the issue anyways. I'm going to say it's the regulator but without you doing test we don't know.





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[No disintegrations]

See attached.

I'm happy to do it, but I do like knowing what people are thinking before I go out and do things though. I was asked to pinch test the return line, not knowing what I'm looking for. Did that, and still don't know why. Helps us all learn when it's explained.

Sorry to keep you out of the loop, I'm just trying to see if a wire was on the wrong cylinder. Double check them if you're not sure.

 

[Boost231]

Also do you know how to change the regulator?

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[Terbro]

You didn't do a pinch test the correct way. You need to block off the return apply power to the jumper wire and see what it does. Should go over 90 imop

If that checks out jump the wire and start applying pressure to the top of the regulator and see what the pressure does. I'm going to guess this is the issue.

A dent tank isn't the issue. Why buy another pump when a new one was just installed. You said you added a ground with no change and I don't belive this is the issue anyways. I'm going to say it's the regulator but without you doing test we don't know.

Firstly, I'll say again that I greatly appreciate the input. But I've been getting suggestions from several people that are very brief, assume I already know how to do a procedure....kind of like saying "make French Toast". It might be a relatively basic procedure for someone who's done it before, but not if one hasn't.

I think I get it now. It sounds like you want me to jump the pump in the same manner one would if draining the tank of pump gas before a race. I did that ~15 years ago, but haven't done it since. I no longer remember how to do it...have only vague memory of there being an available wire on the driver's side, ready hot wire to activate the pump....to keep it running. So I'll need *complete details* on how to jump the pump at the engine bay in order to do that. I was big into TR's years ago (as you can see from when I joined), but I haven't been to the track or cranked wrenches on once since this one in about 12 years. So consider me a newbee in many ways. TR basics, I'll never forget. I just changed my injectors 3 months ago, and it probably took just over an hour, so yes - I can r&r an FPR!

Never meant to imply that a dent was the cause... please, I'm not that stupid. I only mentioned it because I don't like it, cosmetically, and it'd be part of the restoration - and while I'm at it...

Regarding the ground, per Nick's suggestion, I spliced into the existing stock ground wire behind the tank, with a 10-gauge wire, and grounded it to the alternator. Others have mentioned that that's not the right way to do it, and maybe not. A good ground all the way to the pump, entirely replacing the stock ground is undoubtedly the *ideal* way. There's the ideal way, then there's the way to do it which is far easier, and has one hoping it'll help, i.e, "worth a try".

 

[Terbro]

Sorry to keep you out of the loop, I'm just trying to see if a wire was on the wrong cylinder. Double check them if you're not sure.

Yeah, definitely explain first! I could've confirmed that all cylinders are firing fine. I've stated several times in this thread that it runs perfectly up until 15 psi, and 90+% throttle.

 

[Terbro]

Also do you know how to change the regulator?

Piece o' cake... As I've mentioned, I've successfully r&r'ed a TR motor single-handedly start to finish back in '02. I installed a 5-speed T-10 tranny, mated to a 327 V8 in a Datsun 240Z, had to add a custom slave cylinder and clutch, etc. to it as well - all by my me own self. So I'm very capable. But obviously proper guidance was essential, and having the tools was obviously required as well.

 

[Terbro]

Also do you know how to change the regulator?

On the FPR subject, if it turns out to be the culprit, which one is most popular for our TR's? I am on a budget, so there might be some awesome one that's twice as expensive. Not looking for that one - the one that most use with good results.

 

[Boost231]

I like this one

http://www.kirbanperformance.com/pr...ADJUSTABLE+FUEL+PRESSURE+REGULATOR+#6547.html

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