Unexplained Temporary Non-Start Issue

[RyanBorck]

I have an 81 FI Spider.

Issue: Engine will turn over but refuses to start after making a few stops running errands. If I let the car sit for 10-20 minutes, it starts up without issue. Typically occurs after I try to start it up shortly after turning the car off (about the time it takes to run into blockbuster).

Car has been looked up and down by a trusted Fiat mechanic who did notice it had trouble starting up and while trying to figure it out, enough time had passed - it resolved itself and started right up. Fuel injectors have all been replaced and the fuel system from tank to engine has been relined and cleaned.

Originally he thought the issue was tied to the fuel pump. He had to rebuild it twice and since it's been working without a hitch, starts up when the key is turned and doesn't overheat after the key is removed. Thought it might be the cold-start injector but said I would smell gas if that were the case.

Any thoughts?

[So Cal Mark]

you need to hook up a pressure gauge to see if the system holds pressure when shut off. I'm impressed if your guy can "rebuild" an electric pump. Those things are crimped together and I've never seen one that could be "rebuilt" without leaking

[rlux4]

You say that "it starts up when the key is turned". Do you mean the fuel pump starts up when the key is turned? Turned to "on" or turned to "start"? The fuel pump shouldn't come on until the engine is turning over (cranking or running). The non-start issue can usually be caused by either a bad temp sensor in the coolant "T" or an unreliable connection supplying power to the dual relay, which is the source for power to the fuel pump. Do you have a manual for the FI system? Most of them will include a section of troubleshooting. Look up the symptoms, it will give probable causes. I use a couple of them, but a good one to have for sure is Brad Artigue's in his Fiat Engine Maintenance and Modification manual, which includes a section on our Bosch L-Jetronic system:
http://www.artigue.com/?attachment_id=5
Ron

[RyanBorck]

Thanks. It's probably time to start using manuals and learn the inside out of this car.
I meant that when the key is turned to on, you can hear the humming of the fuel pump.

As for the pressure when the car is sitting, any instructional video or handbook on how to do that? I will recommend it the next time it's in the shop but it would be great if i could check on my own.

Thanks again.

[rlux4]

OK, this may come as a shock to you and other Fiat owners, but someone in the past has messed with the stock set up of your car! I guess it's OK to have the dual relay bypassed so that the fuel pump comes on when you turn on the key, but my thinking is the engineers that designed the FI controls knew what they were doing and in stock form the system is very reliable and fairly easy to work on. Also, if a problem needs to be diagnosed, anything that is changed from stock makes it pretty harder to do, following tried and true diagnostic steps. So, without being at the car, troubleshooting help is difficult, because we don't know what, or how changes were made. Not impossible, but difficult. Sort of like shooting in the dark.
If you want to get the car back to stock, let us know, we can help.
For checking the fuel pressure, I got a liquid pressure kit and adapted it to attach to the hose that goes to the cold start valve. Be careful whenever you disconnect any fuel lines though, they are pressurized all the time. The fuel pump puts out about 45 pounds and the pressure regulator (at the firewall end of the fuel rail) regulates that pressure according to the vacuum it gets from the intake manifold.
While you're waiting for the manuals you're ordering to get to you, download and study Brad's manual that I mentioned earlier.
Good luck,
Ron

[RyanBorck]

Wow, that's interesting about the bypass. And I agree completely easier to diagnosis if starting from stock. So the fuel pump is only supposed to turn on as the engine turns over... not just when the key is turned to the on position in it's current setup.

That would be great if it would just be a matter of returning to stock. Or at the very least give me a good launching pad to dig further if necessary. I found a local foreign car mechanic that is going to perform an alignment (I posted in the Suspension category asking anyone if they new a good alignment shop close to Dallas) on the car. I will ask him about the fuel pump being wired to come on before the car actually starts to turnover.

Thanks.

[So Cal Mark]

the constant pump running could be as simple as a misadjusted pump switch in the air flow meter

[rlux4]

Yes, that's a possibility Mark, or the flap is stuck slightly open. But I'd bet the wiring's been altered. Seems like that's the first thing some PO or mechanic who doesn't know the system does to get the pump running.
Are you still having issues with the intermittent non-start, Ryan?
Keep in mind, the cold start injector only comes into play if ambient temperatures are low, say below 70°, if the car is warmed up, it doesn't get the signal to open.
So, if you're fuel pump is definitely running and it''s not starting, I'd check the fuel pressure like Mark suggested, and also your temp sensor in the cooling "T". The other sensors won't cause the car not to start.
Ron

[So Cal Mark]

my suggestion was to determine if the system was holding pressure when shut off. Loss of pressure indicates either a leaking injector(s) which creates flooding and possible vapor lock

[RyanBorck]

Hasn't repeated the non-start symptoms since Friday but I definitely think checking the pressure when sitting and checking the temp sensor in the cooling "T" would be the next step.

Once I learn what the "T" actually is, I will give you all a heads up.

[RyanBorck]

Another piece of info that may or may not relate... I get really bad gas mileage with this car. So either it's related or I have another theory that the car's speedometer just runs slow and is actually driving more miles than it actually records (not bad for making the car look younger but not great if I need to see how many miles I am getting per gallon.

Filled it up, it's nearly empty and the speedometer has only gone about 90 or so miles, ouch!

Ryan-

[rlux4]

The worst mileage I got on my Oregon trip was 25 mpg on one tank. Most of the time it was around 28, and that's probably typical for our cars. (For us who drive like old ladies. No offense meant to the old ladies.) If you have a gps unit that shows speed, you can check the accuracy of your speedometer. Mine shows 5 mph slower than actual speed.
Good point Mark!
Ron

[So Cal Mark]

if the mileage is that poor, I'd check the pressure regulator for leakage into the vacuum hose

[RyanBorck]

Well, she's been running well and I haven't been able to replicate the non-start issue.

Had the alignment finally done of the car and it actually drives straight. The mechanic said that it had probably never been aligned before... ouch.

Next issue of concern... gas mileage... will take vacuum suggestion.