AFM weirdness? - Hard to start cold and hot

[Larry]

I've been diagnosing a weird starting issue and realized something odd yesterday. I have much longer thread already going but want to keep that separate from this.

I've gone through the FI diagnostic manual but still have the hard starting problems when the car is cold and warm.

One thing we did yesterday is when we were trying to start the car, we pushed open the flap in the air flow meter about 1/8" and the car started right up.

The timing is set correctly - that's been verified multiple times. We've replaced the snorkel hose which eliminated a slight leak under one of the clamps and have checked for other vacuum leaks

What's interesting is we swapped in one I purchased from MWB that has been tested in a working car (according to their website). After we swapped it in, the car didn't start when cold but when we opened the flap about 1/8", the car started right up.

 

[Waterbury]

So just to clarify, the car will only start when the flap is 1/8" open? No matter the AFM that is installed?

All wiring to the AFM look good? No cracking or bare wires? Solid grounds?

Also worth checking the throttle maybe? Will it start if you play with the throttle while cranking?

Are you running a stock intake filter pre AFM or something aftermarket?

 

[Dr.Jeff]

Does the flapper door on the AFM move away from its resting point at all while cranking? It needs to open a little to connect the electrical circuit to the fuel pump (as when you manually move it open). Normally cranking the engine provides enough vacuum at the AFM to move the door open enough. Sometimes that door gets "sticky". If it was only happening with one AFM then I'd say the contacts inside are bad or the door (flapper) is sticking. But with the same effect on two AFM's, then I suspect not enough vacuum at the AFM for some reason. You already eliminated some vacuum leaks, make sure there aren't any others. Check for leaks a the cold start valve hoses, dipstick tube, intake manifold, everywhere there is vacuum (basically the entire engine). This design of FI system is very vacuum sensitive, and it is the job of the AFM to measure that vacuum. Aslo is the throttle valve completely closed off (with no force on the accelerator)? It should be open a crack to allow some air past it. There is also a idle speed screw that bypasses the throttle valve. Make sure both of those are not fully shut off. Also measure your engine's vacuum. A badly worn engine can have so little vacuum it won't move the AFM flapper...but that would be severe wear and it would run poorly.

 

[Larry]

So just to clarify, the car will only start when the flap is 1/8" open? No matter the AFM that is installed?

It will start but usually takes a lot of cranking and slight application of throttle. It also does this hot or cold. But sometimes, you turn tbt key and it starts right up when it’s cold.

All wiring to the AFM look good? No cracking or bare wires? Solid grounds?

Yep. I replaced the FI wiring harness with one that had much more supple insulation. The insulation on the one I replaced didn’t bend. It cracked when bent. Both grounds are in place and I even added a 3rd ground.

Also worth checking the throttle maybe? Will it start if you play with the throttle while cranking?

Yep.

Are you running a stock intake filter pre AFM or something aftermarket?

Absolutely stock. Although right now the factory air box isn’t on the car.

 

[ng_randolph]

One thing we did yesterday is when we were trying to start the car, we pushed open the flap in the air flow meter about 1/8" and the car started right up.

The dual relay that operates the fuel pump can be triggered through two paths: Contacts in the AFM that close when the flap opens, and voltage from the "start" contacts in the ignition switch. If your car starts easily with the flap slightly open, I would suspect the contact set in the AFM works just fine, but that there is something wrong with the other path. A simple test would be to disconnect the trigger wire to the starter, and then turn the ignition key to "start". The starter will not engage (obviously), but you should hear the fuel pump run.

If the fuel pump does not run in the above test, check if terminal 86a of the dual relay has battery voltage with the ignition switch in "start". This terminal should have a RED/BLK wire going to it. This RED/BLK wire should come from the connector for the starter trigger terminal, where it is joined by a RED wire from the ignition switch. Wire colors from the "1980-81 Electrical Diagnostic Manual"; the Bertone wiring diagrams show the same colors.

 

[Larry]

Does the flapper door on the AFM move away from its resting point at all while cranking?

I'll have to check. The car isn't here but I will check the next time I'm there.

It needs to open a little to connect the electrical circuit to the fuel pump (as when you manually move it open). Normally cranking the engine provides enough vacuum at the AFM to move the door open enough. Sometimes that door gets "sticky". If it was only happening with one AFM then I'd say the contacts inside are bad or the door (flapper) is sticking. But with the same effect on two AFM's, then I suspect not enough vacuum at the AFM for some reason. You already eliminated some vacuum leaks, make sure there aren't any others. Check for leaks a the cold start valve hoses, dipstick tube, intake manifold, everywhere there is vacuum (basically the entire engine). This design of FI system is very vacuum sensitive, and it is the job of the AFM to measure that vacuum. Aslo is the throttle valve completely closed off (with no force on the accelerator)? It should be open a crack to allow some air past it. There is also a idle speed screw that bypasses the throttle valve. Make sure both of those are not fully shut off.

Thanks. That's given me some things to check.

Also measure your engine's vacuum. A badly worn engine can have so little vacuum it won't move the AFM flapper...but that would be severe wear and it would run poorly.

It's definitely not a badly worn engine. Among other things, we replaced the head along with the brake and clutch master cylinders. Right now we're measuring the engine line in hours and not miles. The first test drive was 3 miles - 1.5 miles driven and 1.5 miles towed after the engine died and wouldn't restart.

 

[Larry]

The dual relay that operates the fuel pump can be triggered through two paths: Contacts in the AFM that close when the flap opens, and voltage from the "start" contacts in the ignition switch. If your car starts easily with the flap slightly open, I would suspect the contact set in the AFM works just fine, but that there is something wrong with the other path. A simple test would be to disconnect the trigger wire to the starter, and then turn the ignition key to "start". The starter will not engage (obviously), but you should hear the fuel pump run.

Right now the fuel pump won't run unless the flap in the AFM is open. I'm assuming it's still okay in this test to push the flap so the pump can engage?

If the fuel pump does not run in the above test, check if terminal 86a of the dual relay has battery voltage with the ignition switch in "start". This terminal should have a RED/BLK wire going to it. This RED/BLK wire should come from the connector for the starter trigger terminal, where it is joined by a RED wire from the ignition switch.

I don't know if this throws a monkey wrench into this, but I replaced the dual relay with one I had on hand. I purchased one several years ago and have one from an '81 Spider I parted out that "ran fine when parked."

Wire colors from the "1980-81 Electrical Diagnostic Manual"; the Bertone wiring diagrams show the same colors.

Thanks. The donor engine/transmission came from an '84.

A question on the dual relay part number. The one that was in the car - this was installed by the mechanic that installed the '84 FI engine/transmission - is 0 332 514 127. The one I swapped in ended in 121 - Part Number: 0 332 514 121. When I looked both up online, they're both listed as a FI combination relays. Looking at our vendor websites, I found the one that ends in 121 is what's listed.

 

[ng_randolph]

Right now the fuel pump won't run unless the flap in the AFM is open. I'm assuming it's still okay in this test to push the flap so the pump can engage?

I don't see that this would be a problem.

A question on the dual relay part number. The one that was in the car - this was installed by the mechanic that installed the '84 FI engine/transmission - is 0 332 514 127. The one I swapped in ended in 121 - Part Number: 0 332 514 121. When I looked both up online, they're both listed as a FI combination relays. Looking at our vendor websites, I found the one that ends in 121 is what's listed.

I know the '121 vs. the '127 has been discussed here before (and on Alfa and BMW boards), but I don't know that a conclusion was reached. I was suspicious of the wiring, not the relay itself (although people here have had these relays fail). Is the RED/BLK wire going to pin 86a of the dual relay connected to the trigger wire for the starter, and in turn to the "start" terminal on the ignition switch?

 

[Larry]

I don't see that this would be a problem.

Cool. Just wanted to be sure.

I know the '121 vs. the '127 has been discussed here before (and on Alfa and BMW boards), but I don't know that a conclusion was reached.

D'oh!! Never thought to search for it....

I was suspicious of the wiring, not the relay itself (although people here have had these relays fail). Is the RED/BLK wire going to pin 86a of the dual relay connected to the trigger wire for the starter, and in turn to the "start" terminal on the ignition switch?

I'll check when I'm at the car next. I suspect so since the car ran fine for the 18 or so years I've had it. The hard starting when hot or cold first appeared in 2019 and has gotten progressively worse.

 

[Larry]

Well as an update.... I was at the car today.

@Dr.Jeff - I'm pretty sure there's no vacuum leaks. We've sprayed starter fluid on most things and feel confident that's not a problem.

On a whim, I decided to see how it would act on starting. The last time we had it running, we set the warm idle to 1500rpm, but the car still had issues starting when warm. On Saturday, It started right up on the first crank, idled fine... never stalled... never dropped idle speed at all - basically acted perfectly normal. I let it idle up to the fan kicked on and after it shut off, I shut the engine off. I let it cool for 20 minutes - this was with the engine cover up. It started right back up again on the first crank. I let it idle back up to the fan kicked on/off. Shut it down again, waited 30 minutes with the engine cover closed and it started right back up on the first crank. Shut it down again, let it sit for 50 minutes with the engine cover closed and it started right back up on first crank.

It was close to dark and the rescue vehicle wasn't available, otherwise I might have taken the car for a drive. But the prospect of it dying a mile or more away without a tow vehicle to help bring the car back kept me from feeling too adventurous.

But this was the first time in I don't know how long it acted "normal."

My guess is something electrical is the issue???

 

[Jefco]

My buddy's new-to-him 124 spider ('81, FI) had a problem running consistently that I solved by finding a connector on the double relay would push out of the socket, giving only a little contact with the terminal on the relay for a while until the vibration could not overcome the corrosion that forms. Investigation found that terminal turned off the fuel pump if not connected.

I think any Fiat double relay will work, I tested his in my X and it worked perfectly (but not in his car for a while).

Sorry, I don't remember the pin # and looking at wiring diagrams has so far not improved my memory, but the connector in question is in the corner of the plastic socket for the double relay, for one of the smaller size terminals.

So make sure each wire is seated securely on its terminal on the double relay when it is inserted in the socket.

 

[Dr.Jeff]

Intermittent stuff like that could be a electrical connection as you say. I know the feeling of not trusting something that mysteriously goes away. Try going through every connector you can find relating to the FI and clean/secure them. Including all of the grounds. Fiat used spade (push-on) terminals for everything. They are not the most reliable type of contact and can become loose or corroded.