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So I have been chasing once again a cold start and die on my L98 and have been through min air adjustment, replaced a faulty FP relay connector/relay. It has been weeks since the issue cropped up the last few days it’s been everyday I drive it.
Today I decided to look at fuel pressure which before had not been an issue. Also I changed the fuel filter last week and before that the previous one only had 10k on it and both had no blockages that I could tell.
After hooking my gauge up with vac hose still attached I am about 35 psi, with it disconnected it’s right at 44/stock where I set it. After searching some threads on here and checking my FSM I mounted the gauge on the windshield so I could see it and took it for a ride to see how it does under load…at WOT and pushing 4500-5k rpm on a deserted back road it won’t go higher than 40psi.
So am I correct in my assumption that the fuel pump is on its way out? It could be original with 89k on it.
If you're at 4.5-5K and running OK (not missing and not lean), pump is not issue because providing volume regardless of pressure. Try this:
Turn key on and immediately start cranking while pump is priming. Don't wait until it's stopped. Could be that pressure is not being maintained after prime ends. Search for tests to perform to determine that, leaking injectors, etc. And are you certain it's priming given the relay was replaced?
If you're at 4.5-5K and running OK (not missing and not lean), pump is not issue because providing volume regardless of pressure. Try this:
Turn key on and immediately start cranking while pump is priming. Don't wait until it's stopped. Could be that pressure is not being maintained after prime ends. Search for tests to perform to determine that, leaking injectors, etc. And are you certain it's priming given the relay was replaced?
Positive it’s priming, you can hear it for sure and it builds pressure, around 40psi IIRC. I noticed that over about 5-6 hours after shut down it bleeds down to 0 psi.
Injectors and FPR are both about 2 years old or so, no smoky long crank start ups and no fuel in vac line for FPR.
I will try that start up without letting it prime and report back.
It started right up when I just put the key in and twisted.
Did you already start it today though? Mine also does the long cold start, but even if it doesn't warm up, the next start is immediate whether I wait for a prime or not.
Not saying my pump is good, actually it's more likely both our pumps are bad. But my afpr is new, injectors are new, line holds pressure for hours, etc.
Did you already start it today though? Mine also does the long cold start, but even if it doesn't warm up, the next start is immediate whether I wait for a prime or not.
Not saying my pump is good, actually it's more likely both our pumps are bad. But my afpr is new, injectors are new, line holds pressure for hours, etc.
Nope, it was first start of the day. Mine actually starts pretty good all the time but the way the pressure completely bled down to 0 when I left the gauge on there after 5-6 hours I was stunned it fired so quick today with just snapping the key and not waiting for it to prime like I always do.
Also the pump is one of the last of the maintenance items I’ve yet to replace and has been on
my radar to get to before it gives up the ghost at the worst possible time.
I also mentioned the pressure of 40psi at WOT while driving the car and a mechanic I know thought that was low.
It started right up when I just put the key in and twisted.
The pump is actually starting to prime (building lost pressure) the instant you turn the key on. So when starting before the 2 second prime period ends, you have fuel pressure in the line enabling it to start and run.
Sure sounds like your pump's check valve is slowly leaking (based on your 5-6 hr pressure test), or you have one or more injectors leaking, because pressure is not being maintained. I'd first perform an injector leak-down test to see if that's the issue. If so, you know what needs to be done . If not leaking, then again, given you can rev to 5K without problems, the pump itself is OK and I'd install a one-way check valve as close to the tank as possible. Something like this: Russell 650603. Expensive at $35-40, but a lot easier to install and less than a pump, etc.
The pump is actually starting to prime (building lost pressure) the instant you turn the key on. So when starting before the 2 second prime period ends, you have fuel pressure in the line enabling it to start and run.
Sure sounds like your pump's check valve is slowly leaking (based on your 5-6 hr pressure test), or you have one or more injectors leaking, because pressure is not being maintained. I'd first perform an injector leak-down test to see if that's the issue. If so, you know what needs to be done . If not leaking, then again, given you can rev to 5K without problems, the pump itself is OK and I'd install a one-way check valve as close to the tank as possible. Something like this: Russell 650603. Expensive at $35-40, but a lot easier to install and less than a pump, etc.
HTH, Elky
I will check out the injectors, but I have none of my old symptoms from when I replaced them a few years back like the long crank times when hot and smoky rich start ups, that will be a real bummer to change them again if they are leaky. Also I just thought at WOT while driving I would be closer to 44psi.
At this point I will likely just replace the pump and sending unit as preventative maintenance and maybe have a tank on hand in case the original is funky. I will report back if I replace the pump etc.
If it's original / doubt, I'd change it...it's 33? years old.
Ive been stranded due to fuel pumps crapping out way too often to trust them. I've had some run perfectly fine then just crap out..Id have others give issues randomly, then act fine but then crap out suddenly as well.
If it's original / doubt, I'd change it...it's 33? years old.
Ive been stranded due to fuel pumps crapping out way too often to trust them. I've had some run perfectly fine then just crap out..Id have others give issues randomly, then act fine but then crap out suddenly as well.
I am with you on this, I’ve been testing more and after bumping up AFPR to 48psi w vacuum disconnected( where I usually have it set) the most it will pull is 42-44 WOT and it’s been holding pressure really well after shutdown…but looking at the tank it looks original/has visible rust on exterior and looks to never have been out so I will likely replace the whole works as preventative maintenance…I daily drive this in the summer for a 100 mile round trip 1 or more times a week and don’t want to be stranded.
I am with you on this, I’ve been testing more and after bumping up AFPR to 48psi w vacuum disconnected( where I usually have it set) the most it will pull is 42-44 WOT and it’s been holding pressure really well after shutdown…but looking at the tank it looks original/has visible rust on exterior and looks to never have been out so I will likely replace the whole works as preventative maintenance…I daily drive this in the summer for a 100 mile round trip 1 or more times a week and don’t want to be stranded.
The pressure aftr shutdown, thats just for quick starts / shows the valve isn;t open rigt?
Mine would hold pressure for a long time after shutdown and would give the correct pressures and then crapped out right after....
Regardless, here's a HORRIBLE scenario..... my firebird left me stranded 20 houses down the street.....that was embarrassing lol
My S-10 seemed to run fine...I daily drove it...then one day the original 200K mile pump from 1990 seemed to act funny..but it ran fine after that.......I ignored it....
As I pulled up to my work parking stall it crapped out completley......so I was stuck......
The pressure aftr shutdown, thats just for quick starts / shows the valve isn;t open rigt?
Mine would hold pressure for a long time after shutdown and would give the correct pressures and then crapped out right after....
Regardless, here's a HORRIBLE scenario..... my firebird left me stranded 20 houses down the street.....that was embarrassing lol
My S-10 seemed to run fine...I daily drove it...then one day the original 200K mile pump from 1990 seemed to act funny..but it ran fine after that.......I ignored it....
As I pulled up to my work parking stall it crapped out completley......so I was stuck......
You might as replace the "UFO" vent valve too.....
Mine gave issues and I believe created a vacuum in the tankl that didn;t allow the pump to pump fuel..
I got stuck on an isolated road 30 miles from home with no cell phone reception..... luckily releiving the gas cap fixed that hahahaha
I actually repaired my original with a thorough disassembling/ cleaning and then replaced it eventually with the Hawks reproduction which is nice quality.
I actually repaired my original with a thorough disassembling/ cleaning and then replaced it eventually with the Hawks reproduction which is nice quality.
How in the world did you
1. Remove it from the bracket without breaking off the tabs
2. open it up without breaking it
That thing was a bear to remove and I gave up trying to open it lol
I did the rollover vent valve mod but then the hawks one came out. I threw in a canister filter to help keep fumes out but so far so good!
1. Remove it from the bracket without breaking off the tabs
2. open it up without breaking it
That thing was a bear to remove and I gave up trying to open it lol
I did the rollover vent valve mod but then the hawks one came out. I threw in a canister filter to help keep fumes out but so far so good!
I might grab one though as a backup from hawks
The part I tore down is that small vent valve right near the axle coming off a rubber fuel hose. There is a old YouTube video by a member by the name of jrobling and it was good.
1. Mine did not have much left for tabs, literally just had to lift it out. I saw on the new one there are prominent tabs to lock it in.
2. Very carefully, that plastic is brittle but I was patient and followed the video. Mine was maybe preserved because of the old undercoating all over it lol…which I think just removing all that was part of the problem. I did notice there was some dirt in there and once it was all cleaned( used my garden hose) up and back together no more noise from venting. Before it made an almost mooing noise while venting.
I was also having some fuel pressure problems on my 350tpi and I wanted to rule out a pump verse a stuck/leaky injector. So I bought some fittings to test directly at the fuel supply rubber hose in engine compartment instead of at the Schrader valve on fuel rail. It gets up to 60psi quick on key on prime but it does not hold pressure so I'm blaming the check valve at the fuel pump itself. Here are the parts I used my fuel pressure tester is a female 4an yours might be different. One m16x1.50 o ring Saginaw fitting ( not sure if thats spelt correct) with a 6an male and then a 6an to 4an reducer
That is pretty slick, never saw anyone test fuel pressure there before but it makes sense.
I wound up just replacing my tank, sending unit,
and fuel pump just right before winter as preventative maintenance. Once the tank was dropped it had a good amount of rust on it…
I didn’t have much time to run the car before putting it away but it ran great. The only rub is the new dorman tank didn’t seem to like to take fuel as well as the original. I tried adjusting the filler neck but will have to wait until spring to see if it’s better.
That is pretty slick, never saw anyone test fuel pressure there before but it makes sense.
I wound up just replacing my tank, sending unit,
and fuel pump just right before winter as preventative maintenance. Once the tank was dropped it had a good amount of rust on it…
I didn’t have much time to run the car before putting it away but it ran great. The only rub is the new dorman tank didn’t seem to like to take fuel as well as the original. I tried adjusting the filler neck but will have to wait until spring to see if it’s better.
Oh really I wonder if the filler neck got a small bend/dent during install that could cause some filling issues.
10-18-2021, 08:35 AM
. But my afpr is new, injectors are new, line holds pressure for hours, etc. 
. If not leaking, then again, given you can rev to 5K without problems, the pump itself is OK and I'd install a one-way check valve as close to the tank as possible. Something like this: Russell 650603. Expensive at $35-40, but a lot easier to install and less than a pump, etc.
