Dropping Fuel Psi

[aarang]

Just a thought,

After installing a Walbro pump in my ZX, when my tank was full the pump was quiet. After the fuel level dropped, the pump got louder and louder. Obviously the pump was cavitating as the fuel level dropped. I had to lower the pump on the bracket to bring it just lower than the bottom of the tank.

I also drilled the pump inlet fitting hole ( barb fitting in my case) to 1/4" as it seems to me the fittings that come with the pump have too small I/D. I think the hole was 3/16" originally. I never did have the fuel pressure problems like you have.

Also, I think someone else mentioned the ethanol in the gas issue. I wonder if these pumps are compatible? Ethanol is definetly not a good pump lubricant!! I don't know if 10% ethanol would be an issue, though.

 

Aaron

[z-ya]

Sorry if you posted this before, but where is you feed and return connected? Did you increase the size of the stock return and retern fitting at the tank?

[Slow_Old_Car]

i'm going to play a different angle here. your fuel issue is emulating a problem i've seen before, though yours is slightly different, it's worth a shot.

 

you are running a MSII-Edis setup. Can you datalog the motor and upload that log for us to look at?

 

What version of the code are you running? What does the MS show for voltage when this problem occurs? Can you get a stethascope on your injectors to hear if there firing pattern becomes irratic when this occurs? Etc...

 

I only say this because you've basically been up and down the fuel system till your blue in the face right now. Might be time to take a break and look into a few other potential avenues.

[TONY C]

I thought about the pump height too but it does it with a full tank also.

 

I didn't increase the return line size or fittings at the tank. Didn't think it was necessary.

So today I didn't bother to drive it. Instead, I made myself a rear sump box. Drained and removed the tank. All the gas was clean. Cut a big a** hole in the tank. Had the tank full of water and as soon as the zizz wheel broke through. BOOM! didn't hurt anything, or me. thank GOD. Cut out the spot for the sump and even though I have cleaned the tank a couple of times there was a fine film if rust on the entire inside. Washed and cleaned it real good. No rust or debris on the inside.

First thing in the morning I am going to get some fittings and weld the box to the tank. This is something I wanted to do anyway. Driving the Dragon regurlarly always makes me wonder about pump cavitation.

 

I'll keep you guys posted tomorrow on what goes on. thanks for all the great help. tc.

[TONY C]

slow old car.

I havn't figured out how to datalog yet. dummy. the code is 29 or.29? something like that.

I have noticed that even when the car is running good when I am in the power and have the pedal to the mat i will get a miss fire, or a slight pop. only 1 per 10 - 15 secs. Might be because the map is rich right now and edis fires 2 plugs at a time. but I am interested to hear your ideas more. tc.

[viperredls1z]

I have been watching this thread for the last 2 days because I am having the same exact problem. and have tried all the same recommendations. even used 2 different pumps to rule out the pump.(this is a car that has been running fine for over 2 years) finally today I rechecked the vent and noticed that even tho it flows air, it wasn't flowing much. so I installed a larger line and it looks like problem solved! I haven't driven it more than 10 min. at a time yet. but it was so bad before I would have noticed in 3-4 minutes.

The first time I checked the vent I used compressed air and the cap was off the tank and you could hear lots of air going through. today I blew through it and could tell there wasn't as much volume of air as you would expect from 1/4 in pipe.

This could be that stupid simple solution you have been looking for. Good Luck.

[REISHOKIN240Z]

Just a thought... in your constants page - injector control. Are you running SIMULTANEOUS or ALTERNATING? From what I’ve read on the MS instructions website SIMULTANEOUS will begin to lower your PSI.

 

As far as your fuel pump growling! I had the same problem when I put an in-line fuel filter in-between my fuel tank and my fuel pump and it started to growl. So I took the in-line fuel filter off and it stopped. Anywho one of two things, ether your not getting the fuel to your pump by restriction (clogging) or by form of setup (like I had...).

 

Also just a question where is your feed line coming from? In order to avoid the double pump e.g. fuel tank to feeder (low pressure pump) to main (high pressure pump) to motor. I took my fuel tank drain plug out and used that as my feed line straight to my high flow. I then set my tank and pump so the bottoms were at the same level so the gravity helps feed the pump.

 

Kinda like a siphoning effect.

 

sorry if this was usless rambling

[REISHOKIN240Z]

heres what it looked like before i took out the restrictive filter

 

heres a shot of the 1/2 nipple 1/2 inch!!!

 

 

[TONY C]

no such thing as a useless ramble here. I will take all I can get.

when I removed the tank today I noticed that the vent hoses were looking, well, 32 years old. So I plan on replacing them as well.

 

viperredls1z. Drive that thing like you stole it and let us know what happens. Sounds like you got it. Gives me hope.

 

After removing the tank I think I might of had an issue with crap in the tank. Since I drove it with the gas cap off, that should have ruled out the vent hoses.?

I am running my injectors alternating. When I first got the car running {a year ago} I had them simultanious and could notice the psi drop and switched to alternating.

 

Oh yeah! just remembered. about a week before the prob. I had an unrelated issue and had to have the car pulled backwards with a chain. Well I hooked to the lower control arm and when the slack was taken up in the chain {too fast} the tank took a hard blow. not enough to dent it but still pretty hard. Now that I think about it. That probably knocked some crap loose.

How would I go about cleaning the pump out if something is in it? Not really a way to back flush it is there? I would guess that there is not anything stuck in it because the prob would be there all the time.?

Man I hope this works. Chasing ghosts is wearing me out. tc.

[mom'sZ]

Tony, just wanted to add some little stuff. you seem to think fuel lines can only suck shut inside on the suction side of the system. Not true, a worn line can collapse internally under pressure! I've seen it. Also, is there any way you can rig up to pump fuel through the system into a bucket or something on the injector end of the system? Maybe pump it back into the tank and let it run for awhile? Test the entire system up to the point it enters the rail? I bought a cheapy fuel pressure gauge at the auto parts store, one thats made for testing fuel injection systems, for 15 -20 bucks. Rigged it up with a tee fitting. Later I bought one of those little ones that goes on the rail from summit. Be nice to be able to watch as the problem occurs. Good luck man you'll get it, you've got some pretty big guns out on this one, you'll get it. Keep us informed.

[Daeron]

I am no genius, no guru.. I'm only 26 and havent played anywhere NEAR as much as I would like to, yet... but my advice is to take a day off ENTIRELY. DONT come to the forum, don't think about it, just WALK AWAY for a day.. come back and slowly, carefully re evaluate your problem from the get go.

 

In my experience, whenever I get to his point it is because I have missed something BRUTALLY obvious... its like looking for your keys. You tear the whole house apart for an hour.. then realize how angry you will be when you find them at how obvious it REALLY was in the end...

 

Take a breather and forget what you know about the problem. Come back and discover it again. The forgetting is the most important part, because my bet is that you have overlooked something.

 

Hope this helps, and good luck.. you DO seem to have something of a nipple-twister here....

[caszboy]

YOU ARE NOT ALONE. i am having the same problem on my 1974 260z. its carburated and i have a electric fuel pump installed. I just got done..

 

-cleaning out the entire tank

-replacing fuel lines/vent hoses

-eliminated the vent tank to simplify things (plus all the hoses where kinked anyways)

-replaced all fuel filters.

 

The problem has been getting progressively worse and worse. I thought it was temperature related (still might be) but today the temp dropped like 15-20 degrees here and i still have the problem.

 

Also, my fuel pump goes form loud to quite and back and forth and i cant figure it out. Im going to go pick up a fuel pressure gauge today or tomorrow for carbed cars and see what it is at the rail.

 

Im going to be following your thread a lot i think ;p

[TONY C]

Hello fellas, I'm back. well I fabbed a sump box, welded in 2 -8an fiffings in it and welded it to the bottom of the tank, filled it with water to find the leaks and attended to those. washed it out for a couple hours while dragging a magnet to the inside. rinsed it out with a couple quarts of M.E.K. and blew compressed air in it for a while. Then I poured in a quart of RED KOTE by damon products. It's like a red candy syrup that is the most VILE, head busten, buzz inducing stuff I have ever used. WOW. even using it outside is like, WOW!

Well if it works as good as it smells bad, any and all potential for leaks will be non existant. I used a metal funnel when i poured it in and let it dry on the funnel. No way could it be scraped off and even my wire brush on an angle grinder had a rough time with it.

So I have to let it cure for 24 and paint it all up. Can't go without paint.

I will put it back tomorrow.

While I was at it I lowered my pump as much as the bracket allows. I am sure this will help because the walbro is more of a pusher pump.

I'll let you guys know what happens tomorrow. Keepin my toes crossed. tc.

[TONY C]

SUCCESS!!!! Painted and reinstalled. Blew out all the lines, Replaced the vents. Filled it with gas and drove. I drove it hard for 20 miles. All is well.

Not crazy about being able to see the sump and fuel line from the back but function over form for now.

I was looking at an RCI aluminum 17 gal fuel tank. Can't remember the part # but it is the only lay down 17 gal they sell. Looks like it could be easily installed in the z. Anyone know if it has been done with this tank?

Anyway. the sock screen must have been the problem. too bad there is no way to replace it or something. Washing the tank and blowing through it did no good.

Thanks for all the help from all the Hybrid members. Best brothers from a different mother I ever had. tc.

[Pop N Wood]

I was hoping it would be success post.

 

You took a lot of restriction out of the intake line to the pump. I bet it was the combination of that and lowering the pump.

 

As you ran, the fuel in the tank would be heated up from being circulated over the engine and through the return regulator. That little bit of head loss on the intake path would cause the pump to cavitate (boil the fuel in the low pressue intake of the pump). Warmer fuels more readily boil.

 

Post some burn out vids.