78 FI Super Convert.Will Not Start When Hot.

[lakes73]

The Bug will start right up in the cool morning..I will go for a short drive and all is fine..When I get home,shut the car off,wait 30 min,The car will crank and crank,no start...The AFM lil door is now closed,but if I push in on the door,the fuel pump will come on,and she will start....I send it away to get rebuilt..got it back..now the bug will not start at all,even if I push in and open the AFM flap...Also,the flap seems to need ten times the force needed to move it then before I sent it to be fixed.Help!..Summer is short here in Michigan,and I haven`t had a chance to drive her..Any help would be great.Thanks! Chris.

[vwlover77]

What was rebuilt? The engine or the AFM?

One thing to check is the Temp Sensor II on the cylinder head. If it is loose, disconnected, or has a bad connection, it will not tell the computer that the engine is warm. The result will be a fuel mixture that's OK for a cold engine but way too rich for a warm one.

[lakes73]

Hey Don,The AFM was rebuilt..I replaced the Temp Sensor,but I will re-check it..I sent the AFM back to have them check it again,hope to get it back this week..I need to get the beetle running for the Dream Cruz August 18 here in Royal Oak,MI..Thanks for the quick response.Chris.noob.

[Amskeptic]

The Bug will start right up in the cool morning..I will go for a short drive and all is fine..When I get home,shut the car off,wait 30 min,The car will crank and crank,no start...The AFM lil door is now closed,but if I push in on the door,the fuel pump will come on,and she will start....I send it away to get rebuilt..got it back..now the bug will not start at all,even if I push in and open the AFM flap...Also,the flap seems to need ten times the force needed to move it then before I sent it to be fixed.Help!..Summer is short here in Michigan,and I haven`t had a chance to drive her..Any help would be great.Thanks! Chris.

Experiment:
warm engine at no-start condition -
Run fuel pump for one minute (ignition on move AFM flap).
Now attempt to start.
Better?
You have a failed check valve in either fuel pump or regulator. Verify with pressure gauge. Should hold over 14 psi for fifteen minutes.
Colin
Colin

[lakes73]

Thanks Colin,I will do this when I get the AFM back,and will post what I find.Chris.

[lakes73]

Hey Colin,Got re-built AFM back last night..the bug started right up..ran great..drove for 15 min,up to 65mph..Got home..Would not re-start..crank and crank..Pushed in on AFM flap w/key on..fuel pump would not come on..Did Randy of Maine hot-no-start checks..All was fine..But when I clamp the return fuel line after fuel pressure regulator for a few secs the fuel pressure goes up to 80+What should I check next?..Is the FPReg.bad? Thanks,Chris.

[SlowLane]

Pushed in on AFM flap w/key on..fuel pump would not come on..Did Randy of Maine hot-no-start checks..All was fine..But when I clamp the return fuel line after fuel pressure regulator for a few secs the fuel pressure goes up to 80+

This sequence of events is confusing. If the pump isn't running, then you won't get any pressure. How did you end up with 80+psi if the pump isn't running? Did the Randy-in-Maine procedures get the pump running again?

FWIW, seeing 80+ psi with the return line blocked doesn't mean the pressure regulator is bad. By doing so you are basically preventing the regulator from doing its job. It'd be like taking a leak and suddenly putting a stranglehold on your unit. Pressure's gonna build.

[lakes73]

Hey SlowLane,Sorry,my seq.of events are wrong..The car ran fine with the new AFM..Drove around for 20 min..Came home..Shut the car off..Tried to re-start..Crank-n-Crank..No Start..Push in on AFM flap,fuel pump will not come on..The next morning,when the car was cool,she started right up..that is when I did the Randy-in-Main hot engine test...The fuel pressure was around 30 psi,and never dropped below 15psi after 20min..The car runs great when cold,but the fuel pump will not come on when the engine is hot..even if I push in in the AFM flap..HELP!!!..I wan`t to get her running by Saturday so I can drive her to the Woodward Dream Cruz here in Michigan..Any help would be great..Thank You.Chris.

[drober23]

The fuel pump does not come on when the engine is hot, but the starter turns over?. This leaves us three possibilities that I can see.
1) Suspect wiring from the starter to the double relay (test with multimeter), or between double relay and fuel pump (can also test with a multimeter)
2) Suspect double relay (try tapping it gently when this condition is occurring)
3) Fuel pump problem?

My first test would be (when fuel pump is not on) to prop the afm door open and test to see if the starter voltage is reaching the double relay. The Double Relay Troubleshooting sticky in this forum will give you the all the terminal numbers and other info you need for the tests.

[lakes73]

Hey DJ,I replaced the Double Relay..All the wiring checked out ok..will replace the fuel pressure reg.next..check the #3 cyl.sensor also today..Hate to buy a new fuel pump if I don`t need one,but that might be my last hope..Also,the fuel pump will not run,even with AFM flap pushed open by hand if the outside temp.is above 85 degrees..Chris.

[SlowLane]

I think you've narrowed it down to either:
1) The fuel pump is intermittent and not wanting to run when hot, or
2) Something in the circuit supplying power to the fuel pump is refusing to deliver when it is hot.
To find out which, put a voltmeter across the fuel pump's terminals when it is refusing to go and move the AFM flap. Enlist some help if you can't see the voltmeter while moving the flap. If you see ~12V, then the pump is the problem. If you see zero or low voltage, then something's awry with the supply: either a bad relay or poor wiring connections.

If you have a set of LoadPro test leads you can use them in place of the fuel pump in the circuit and evaluate the health of the circuit itself.

Don't worry about the fuel pressure regulator until you've sorted out the pump issue. Odds are the FPR is just fine.

[lakes73]

Ok,I`ll let you know.Thanks Again.Chris.

[Amskeptic]

Ok,I`ll let you know.Thanks Again.Chris.

Stay focused. Do not willy nilly replace parts. SlowLane seems close. Heat related electrical failure. Relay or pump. If you replaced relay, then pump. When at no-start, move wiper, keep there, check for 12 volts at pump terminals, gotta go!
Colin

[lakes73]

If I`m getting low power or no power at the fuel pump,what is my next step to fix this problem? Thanks in Advance.Chris.

[SlowLane]

If I`m getting low power or no power at the fuel pump,what is my next step to fix this problem?

Next most likely culprits would be the double relay, which you say you've already replaced, the ignition switch, the switch in the AFM, and the wiring connections in both the pump power relay circuit and the relay activation circuit. There's a remote possibility that it could be your ECU, but don't go there yet.