Fuel Starvation???

[SSuspect]

Hi all,

First, I will say that I still need to do all of the base tuning on the carbs, but I think that I have another issue. I am hoping (and assuming) that this is something simple. I am just not very good with the "dual carb" thing yet...

Quick Summary

- 1971 240Z - Mechanical pump removed - Electric pump installed on frame rail near tank

- Brand new L28

- Brand new Z-Therapy SU's - Maybe 1 hour of run time total

- E12-80 Electronic disti with MSD Coil

- Current Fuel Pump = New Carter P4070 - 6PSI

- Routing = Tank --> In-Line Fuel Filter --> Fuel Pump --> Lines --> Front Fuel Filter --> In Line FP Gauge --> Carb Feeded Line --> Carbs --> Return Line

Issue

- Key on and great fuel pressure

- Start car and runs great for a minute or so and then stumbles and dies

- Not maintaining strong fuel pressure once car starts.

I have tried 2 pumps so far. NEW RX7 pump and the NEW Carter. Have tried with and without a regulator (Holley). Same result.

Fuel tank was boiled out and is very clean. - Fuel lines blown out with compressed air. ALL NEW LINES INSTALLED FOR EVAP SYSTEM.

Would carburetor adjustment (float level?) cause this problem?

Maybe something in the evap system causing issues? I am thinking of tearing it all out anyway.

This problem was in place with the last engine (smoker) and the NEW one. I have never driven this car yet.

Any input would be greatly appreciated!

Thanks all.

Tim

Edited February 21, 2011 by SSuspect

[Bruce Palmer]

Exactly when and how does this starvation problem show up? After the engine shuts off is the fuel pump still running?

Happened on the last engine and this engine and you haven't driven this one yet? Old and confused, so very very confused..... nyuck nyuck

Do not adjust the floats......

Edited February 21, 2011 by Bruce Palmer

[Gary in NJ]

Have you put a fuel pressure gauge on the fuel line to confirm that the pressure is dropping during operation, or are you assuming that is the cause?

You may have a vapor lock issue within the tank and fuel lines (and yes, the evap system). Try starting and running the engine with the fuel cap removed. In fact, if there is a rush of air when you remove the cap, you do have a vapor lock issue.

You can check the float height (and changes thereto) by making an external float height gauge with some clear tubing. An idling engine should not produce a significant change in the fuel height within the chamber.

[SSuspect]

Exactly when and how does this starvation problem show up? After the engine shuts off is the fuel pump still running?

Happened on the last engine and this engine and you haven't driven this one yet? Old and confused, so very very confused..... nyuck nyuck

Do not adjust the floats......

Hi Bruce... Thanks for the reply! I am confused (and pretty old) too!

When? - 45-60 seconds after car fires up. Choke on. Seems to run the bowls dry and sputters/dies.

Yes - Pump is still running after engine stops. Can start car back up after a few seconds and it does the same thing again!

Old engine - 2.8 from ZX. Was a smoking pig, but ran OK (and had the same fuel issue). I have never driven the car. Was only installed and run for a short period until I got the new engine. Engine fires right up and runs GREAT until the fuel runs out...

It is almost like the pump is not keeping up with the needs of the engine, but it is strange. Should be plenty of pressure!

I am going to replace the rear "in line" filter - cheap insurance. Maybe some sort of blockage at the tank outlet...

Hope that helps a little.

Thanks again Bruce!

Tim

FYI - Here is how your carbs look in my setup...

Edited February 21, 2011 by SSuspect

[SSuspect]

Have you put a fuel pressure gauge on the fuel line to confirm that the pressure is dropping during operation, or are you assuming that is the cause?

You may have a vapor lock issue within the tank and fuel lines (and yes, the evap system). Try starting and running the engine with the fuel cap removed. In fact, if there is a rush of air when you remove the cap, you do have a vapor lock issue.

You can check the float height (and changes thereto) by making an external float height gauge with some clear tubing. An idling engine should not produce a significant change in the fuel height within the chamber.

Thanks Gary! I do have an in-line gauge (visible in pic above reply to Bruce). I also have a fuel pressure regulator mounted and in place. Shows about 4PSI until the car starts and then drops down to nearly nothing! This issue happens with and without the FPR in place.

I will try the fuel cap test tonight when I get home. Good input! I will mess with the float level after I am done with the fuel cap test.

Thanks again!

Tim

Edited February 21, 2011 by SSuspect

[Bruce Palmer]

What kind of induction system did the 2.8 have?

I'd get a large container and take a fuel line in the engine compartment loose and just let the fuel pump run and see, if a minute or two into the run, the volume drops off significantly.

Then unhook the gas line on the upstream side of the filter in question and let 'er run. Probably looking for greater flow rate here more than anything.

OR..... just replace that filter and see what that does.

You say after it dies it takes a bit before it fires up again. I'm guessing that is a delay in refilling the float bowls, hence constricted volume, me thinks.

[LeonV]

I don't know if that picture you posted of the engine bay is current or not, but your vac advance hose is disconnected causing a vacuum leak. It may not be the issue but it is something that would make the car run poorly.

[SSuspect]

What kind of induction system did the 2.8 have?

I'd get a large container and take a fuel line in the engine compartment loose and just let the fuel pump run and see, if a minute or two into the run, the volume drops off significantly.

Then unhook the gas line on the upstream side of the filter in question and let 'er run. Probably looking for greater flow rate here more than anything.

OR..... just replace that filter and see what that does.

You say after it dies it takes a bit before it fires up again. I'm guessing that is a delay in refilling the float bowls, hence constricted volume, me thinks.

Thanks Bruce! I will do that tonight! I love working on these! Everything is SO easy to get to!

I will run it with the current filter in place and then after the replacement. Nothing like a little bit of "before and after" benchmarking...

Yes - I also think that the short delay is due to the bowls filling back up.

I do not have any history on the 2.8. It was never run once it was installed. My friend and I got the car CHEAP and it had the new engine and a lot of other goodies.

I don't know if that picture you posted of the engine bay is current or not, but your vac advance hose is disconnected causing a vacuum leak. It may not be the issue but it is something that would make the car run poorly.

Thanks Leon - good eye! That is an older pic. That line is now hooked up to the dizzy.

Edited February 21, 2011 by SSuspect

[SSuspect]

Bear with me for a second. At least this only took about 10 minutes from start to finish to figure out!

It is definitely a "Fuel Starvation" issue! That's what happens when the fuel pump STOPS RUNNING after you start the car up!! :stupid:

First - Unplugged the fuel line at the fuel dusrtibution rail. Turned key on and fresh, clear fuel flows like a Rocky Mountain stream. No problem there - check that off the list!

Second, start it up and go to check the gas cap for the vapor lock issue. Due to the fact that I have an OPEN HEADER, I am in the garage and the car is choked up to about 1800 RPM, I can't "hear" if there is any suction at the cap to filler neck seal. ARGHHH!!! :tapemouth

So - Since I am back by the tank, I decide to see if there are any visible drips or issues. I bend down and notice that I can't hear the pump running (the Carter is pretty loud). I put my hand on it and SURE ENOUGH - IT IS NOT RUNNING! SON-OF-A-B*&%^!

- The pump runs when the key is on

- I need to see if it runs when the solenoid is activated while starting - it should!

- Fuel pump STOPS running when engine starts!

All I could do was laugh! It has been like this for WELL over a year. But, the car has been torn apart until now and I never needed it to "really" run!

Anyway, I now "think" that I have 1 of 2 things happening.

1 - Wires are crossed on Oil Pressure switch. Not sure which ones yet - 3 wire switch.

2 - Oil pressure switch is toast

Any other ideas?

Here is the link to the Oil Pressure Switch instructions: http://www.holley.com/data/Products/Technical/199R9680-1rev.pdf

I'm not messing with it tonight (now that I know where the issue lies). I have EVERYTHING very neatly tucked into wire loom and I do not want to start into it until I can take my time and trace the wires. Fuel and electrical issues = bad news!

Thanks for the help and motivation guys! These forums are GREAT!

Tim

Edited February 22, 2011 by SSuspect

[Bruce Palmer]

I did my part when I asked the question...... Even a blind hog.... etc. etc. etc.

[SSuspect]

Thanks Bruce!

The funny part is when you asked "After the engine shuts off is the fuel pump still running?", the answer was "Yes", but the truth was that it started up AFTER the engine died and I just assumed that it was running the whole time! I just could not hear it to know it! :embarrass:

Oh well - live and learn. It will be nice to hear this car run "right" within the next few days...

Thanks again,

Tim

[Bruce Palmer]

Yep, getting the "fuel pump running" thing in synch with the "engine running" thing certainly ought to be a priority. Nyuck nyuck.....