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losing fuel pressure 1997 3800Sc by Lou6t4gto
Started on: 02-18-2015 04:20 PM
Replies: 22 (300 views)
Last post by: Darth Fiero on 02-27-2015 03:53 PM
Lou6t4gto
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Report this Post02-18-2015 04:20 PM Click Here to See the Profile for Lou6t4gtoClick Here to Email Lou6t4gtoSend a Private Message to Lou6t4gtoEdit/Delete MessageReply w/QuoteDirect Link to This Post
turn on the key , pump uns it's "few seconds", get to 50 PSI and Immediately starts to drop to 15 (Within about 10-12 seconds ! NO "External leaks" . So, Now what ?
( I am needing to swap the original pump to a new updated one I have anyway) what else can it be ? CAN it be the old PUMP ?
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hiwil88formula
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Report this Post02-18-2015 04:41 PM Click Here to See the Profile for hiwil88formulaClick Here to Email hiwil88formulaSend a Private Message to hiwil88formulaEdit/Delete MessageReply w/QuoteDirect Link to This Post
Yup it can be the pump, I believe they have a check valve in them and it sounds like yours is going out. Had it happen to one I was working on, replaced the pump and problem solved.
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Lou6t4gto
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Report this Post02-18-2015 04:50 PM Click Here to See the Profile for Lou6t4gtoClick Here to Email Lou6t4gtoSend a Private Message to Lou6t4gtoEdit/Delete MessageReply w/QuoteDirect Link to This Post
That would be Nice ! solving the problem by doing what I need Anyway !
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Justinbart
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Report this Post02-18-2015 06:24 PM Click Here to See the Profile for JustinbartSend a Private Message to JustinbartEdit/Delete MessageReply w/QuoteDirect Link to This Post
Bad check valve or split or loose line in the tank.

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Lou6t4gto
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Report this Post02-19-2015 01:39 AM Click Here to See the Profile for Lou6t4gtoClick Here to Email Lou6t4gtoSend a Private Message to Lou6t4gtoEdit/Delete MessageReply w/QuoteDirect Link to This Post
Thanks. I'll post back when I get a chance to drop the tank.
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johnguzman1212
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Report this Post02-19-2015 02:23 PM Click Here to See the Profile for johnguzman1212Click Here to Email johnguzman1212Send a Private Message to johnguzman1212Edit/Delete MessageReply w/QuoteDirect Link to This Post
what pump you using? yeah maybe torn hose in tank ive had that happen already replaced pump
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Riddick85
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Report this Post02-19-2015 05:56 PM Click Here to See the Profile for Riddick85Send a Private Message to Riddick85Edit/Delete MessageReply w/QuoteDirect Link to This Post
If you still have the issue once you change the fuel pump it could be injector leak down. Might have a bad injector or just need to clean them. It is easy enough to get the fuel rail off the a 3800 so take it off, get a small pan with fuel injector cleaner, set them in there and click them with a battery and some leads. DO THIS OUTSIDE! You will be making a small spark and there will be gas and cleaner around and could ignite. I did this to some old fiero injectors that had leak down. I let them sit for a day to evaporate the gas and this made the car run correctly and not be so rich. Be careful if you do it this way and maybe it would be good to do them one at a time.
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Lou6t4gto
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Report this Post02-19-2015 06:26 PM Click Here to See the Profile for Lou6t4gtoClick Here to Email Lou6t4gtoSend a Private Message to Lou6t4gtoEdit/Delete MessageReply w/QuoteDirect Link to This Post
I did that with a 3.4 that I built (1 at a time with a 9 volt battery) I'm hoping it's the pump or Hose , It drops so Fast, from 50 to 15 in 10 seconds, that's a pretty big leak ! well, I'll do the pump and go from there.
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darbysan
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Report this Post02-20-2015 10:42 AM Click Here to See the Profile for darbysanClick Here to Email darbysanSend a Private Message to darbysanEdit/Delete MessageReply w/QuoteDirect Link to This Post
If you are getting to 50 PSI, sounds like the pump is working correctly, and there is no split in the hose in the tank. Otherwise, you would not be able to get up to pressure. Might try disconnecting the fuel line at the rail and hooking your pressure gauge to the line. Then prime the pump and see if it holds. Might keep you from having to drop the tank

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Lou6t4gto
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Report this Post02-20-2015 01:08 PM Click Here to See the Profile for Lou6t4gtoClick Here to Email Lou6t4gtoSend a Private Message to Lou6t4gtoEdit/Delete MessageReply w/QuoteDirect Link to This Post
Have to drop the tank anyway. the orig 2.8 Fuel pump is still in there. (well, I didn't put one in. ) I already Have the New pump to "supply" the 3800SC, just haven't gotten around to installing it yet. thanks
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Lou6t4gto
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Report this Post02-20-2015 01:12 PM Click Here to See the Profile for Lou6t4gtoClick Here to Email Lou6t4gtoSend a Private Message to Lou6t4gtoEdit/Delete MessageReply w/QuoteDirect Link to This Post

Lou6t4gto

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Could it be the Regulator ? WHAT keeps the fuel from coming UP and Not going right back Down the "return line" ? Regulator, correct ? anyone got a thread on changing it ? (3800SC)
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Lou6t4gto
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Report this Post02-24-2015 01:17 PM Click Here to See the Profile for Lou6t4gtoClick Here to Email Lou6t4gtoSend a Private Message to Lou6t4gtoEdit/Delete MessageReply w/QuoteDirect Link to This Post
I dropped the tank, in my 50 years of working on old cars, I have never seen a CLEANER fuel Tank/ sender, and lines !(all like brand new). I installed a new pump for a LT1, now holds 43 PSI for 10 min with the key" shut off", and 43 while running ! YES !
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Darth Fiero
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Report this Post02-24-2015 06:24 PM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Lou6t4gto:

I dropped the tank, in my 50 years of working on old cars, I have never seen a CLEANER fuel Tank/ sender, and lines !(all like brand new). I installed a new pump for a LT1, now holds 43 PSI for 10 min with the key" shut off", and 43 while running ! YES !


What's your fuel pressure doing at full throttle w/ max boost?

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Lou6t4gto
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Report this Post02-24-2015 07:07 PM Click Here to See the Profile for Lou6t4gtoClick Here to Email Lou6t4gtoSend a Private Message to Lou6t4gtoEdit/Delete MessageReply w/QuoteDirect Link to This Post
Haven't taken it out on the road after changing the pump. even if I did, I'm using a "screw on gauge" that can only be Seen in the "engine compartment".
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Darth Fiero
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Report this Post02-24-2015 08:26 PM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
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Originally posted by Lou6t4gto:

Haven't taken it out on the road after changing the pump. even if I did, I'm using a "screw on gauge" that can only be Seen in the "engine compartment".


It wouldn't be a bad idea to get a gauge with a hose on it, tape the gauge to the back window, and have a passenger watch it while you drive so you can see what it is doing at full throttle.

Static pressure (no vac or boost acting on regulator) should be around 50psi.

Fuel pressure with boost should be 1psi rise over static with every pound of boost present.

So if your blower is making 10psi of boost, you should be seeing about 60psi of fuel pressure and it should not drop as RPMs increase (as long as boost pressure remains the same). If the fuel pressure drops as RPMs rise (and boost stays the same), then your LT1 pump isn't able to keep up with the demands of the engine.
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Lou6t4gto
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Report this Post02-25-2015 12:32 AM Click Here to See the Profile for Lou6t4gtoClick Here to Email Lou6t4gtoSend a Private Message to Lou6t4gtoEdit/Delete MessageReply w/QuoteDirect Link to This Post
so, the" 3800SCs "regulator" determines the PSI ? On my LT1 firebird, it's 43 PSI, I would think if this pump can feed a ported/ polished /cammed LT1 (350), it should supply a 231 cube 3.8 . I know the Boost requires more fuel, but taking into consideration that it's 120 cubes LESS..... ?
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Darth Fiero
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Report this Post02-25-2015 02:43 PM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Lou6t4gto:

so, the" 3800SCs "regulator" determines the PSI ? On my LT1 firebird, it's 43 PSI, I would think if this pump can feed a ported/ polished /cammed LT1 (350), it should supply a 231 cube 3.8 . I know the Boost requires more fuel, but taking into consideration that it's 120 cubes LESS..... ?


1) Cubic inch displacement doesn't have as much to do with it as you think. By nature, boosted (either via supercharger or turbocharger) engines require more fuel per HP they make vs. naturally aspirated engines. This would be no different if you put a supercharger on a 350 SBC V8 (it too would need more fuel per HP it produced with the boost). For more info, look up "Brake Specific Fuel Consumption" factor.

2) A naturally aspirated LT1 engine runs a maximum fuel pressure of about 47 psi. The 3800 Series 2 SC demands about 60 or so PSI at full boost. The higher the pressure demanded of the pump, the lower volume of fuel flow it will output. This is true of any fuel pump. My point is the LT1 pump was designed for a max 47 psi fuel system and you're going to be demanding 60 or so psi from it. You had better make sure the LT1 pump you are using is up to the task. It very well may be. But if you don't check, you're not going to know. And if it falls short of supplying your 3800 SC engine with the fuel it demands, it could cost you an engine.

This topic has been beat to death in the past. So I'm not going into any more detail in this thread about it. All I'm suggesting is you check your fuel pressure at WOT so you can make sure the fuel pump you are using can keep up with the demands of your engine. If it turns out your LT1 pump can keep up - great. You should have no problems. But you're not going to know unless you check, are you?

-ryan
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Lou6t4gto
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Report this Post02-25-2015 03:40 PM Click Here to See the Profile for Lou6t4gtoClick Here to Email Lou6t4gtoSend a Private Message to Lou6t4gtoEdit/Delete MessageReply w/QuoteDirect Link to This Post
So, the only way to Know is to tape the gauge to the rear window and have someone else watch it. OK. That may be awhile from now. it's not ready to go out on the road yet. thanks
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Darth Fiero
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Report this Post02-25-2015 04:07 PM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Lou6t4gto:

So, the only way to Know is to tape the gauge to the rear window and have someone else watch it. OK. That may be awhile from now. it's not ready to go out on the road yet. thanks


Correct. But all you need to do is just check it once - and yes, you'll need to be driving in order to do this (unless you put the car on a chassis dyno). It's not like you need to leave that gauge taped to the back window permanently.

Once you've verified your pump can keep up, then you should be ok, unless you later change something on the engine (ie: install performance upgrades); which if you do that, it wouldn't be a bad idea to check it again.
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Lou6t4gto
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Report this Post02-25-2015 05:29 PM Click Here to See the Profile for Lou6t4gtoClick Here to Email Lou6t4gtoSend a Private Message to Lou6t4gtoEdit/Delete MessageReply w/QuoteDirect Link to This Post
Just in Case it isn't enough, Will a 1997 Riviera PUMP "FIT" for the Fiero sender ? (that's what the engine is from. bone stock, but All New) I don't plan on smaller pullies or anything else. Thanks
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Darth Fiero
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Report this Post02-26-2015 02:11 PM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Lou6t4gto:

Just in Case it isn't enough, Will a 1997 Riviera PUMP "FIT" for the Fiero sender ? (that's what the engine is from. bone stock, but All New) I don't plan on smaller pullies or anything else. Thanks


I don't think so. I'm pretty sure the 97 Riviera pump was designed to work in the fuel canister unit which means such a pump would have a secondary output for the venturi pump in the bottom of the canister. And you can't run the canister in a Fiero tank - it won't fit. You can't use a pump from a canister unit unless you plug the secondary fuel output port that was meant for the venturi.
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Lou6t4gto
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Report this Post02-26-2015 02:25 PM Click Here to See the Profile for Lou6t4gtoClick Here to Email Lou6t4gtoSend a Private Message to Lou6t4gtoEdit/Delete MessageReply w/QuoteDirect Link to This Post
OK , Thanks. "Thought", I could keep it simple. I'll wait and see. may indeed end up with the walbro.
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Darth Fiero
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Report this Post02-27-2015 03:53 PM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroEdit/Delete MessageReply w/QuoteDirect Link to This Post
I wouldn't jump to any conclusions just yet until you've had the chance to actually test your current pump. If it can keep up, then you're fine and you don't need to "upgrade".
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