Sputtering at high rpm’s.

WadiaAbushanab · Post by **WadiaAbushanab** » Tue Aug 29, 2023 8:01 pm

I recently just started having this issue on my 1980 Fiat spider 124 Carbureted. If I go full throttle it seems like the throttle or something cuts out at high rpm’s or like it sputters, and it will not go higher than 5k rpm’s, like it hits some hard barrier. Any ideas? I have no clue.

charlielucky · Post by **charlielucky** » Wed Aug 30, 2023 2:01 am

HI, I have an 81 injected model and my engine splutters and dies at 3500 revs. I've been posting about this problem and people have kindly given me some suggestions but unfortunately I can't find a solution. I'll follow your thread to see if anybody comes up with something else to try.
charlielucky

charlielucky · Post by **charlielucky** » Tue Sep 12, 2023 11:02 am

Hi Everybody,

I am running out of ideas on how to get my 81 model running over 3500 rpm. I've purchased a new fuel pressure regulator but I'm having a terrible time trying to get the old on off the car. I want to remove it without removing the fuel rail but the nuts will just not move. Is there some trick I'm missing?

18Fiatsandcounting · Post by **18Fiatsandcounting** » Tue Sep 12, 2023 11:56 am

There is no trick, but those nuts on the fuel pressure regulator can be pretty tight. Perhaps find a stronger friend?

As to the sputtering problem over 3500 rpm... Does it have this problem only when driving (under load) or does it also sputter when the car is sitting in the garage or driveway and you just rev the engine? If only under load, I'd suspect a fuel delivery issue. If it does it all the time, then I'm more inclined to suspect an ignition problem.

Wish I could help you more, but I'm just not very familiar with fuel injected spiders. If you haven't already, I would sign up with Mirafiori.com, and they have a fuel injection diagnostic manual in their library. Someone there might be able to help you as well.

-Bryan

charlielucky · Post by **charlielucky** » Tue Sep 12, 2023 12:11 pm

Hi Bryan, Thank you again for your help. I'm afraid the spluttering out problem occurs even when the car is sitting in the garage. The fuel regulator only cost me 80 euros so as the pressure on the cold start was below 3bar I thought it would be just as well to change it. If it still has the problem even with the new regulator I'm going to need some expert help.

all the best

Charlie

18Fiatsandcounting · Post by **18Fiatsandcounting** » Tue Sep 12, 2023 4:54 pm

Good luck with it, Charlie. I'm sorta familiar with how the FI system works in general, but all my cars are early spiders so I don't have any direct experience. Common trouble spots are the Coolant Temperature Sensor (CTS), the Cold Start Injector (CSI), or the Thermal Time Switch under the intake manifold (TTS). The AFM can also cause problems if it is sticking, and air leaks in that large air duct over the top of the engine can create problems with the FI system. Confuses the Electronic Control Unit (ECU).

-Bryan

charlielucky · Post by **charlielucky** » Wed Sep 13, 2023 3:56 am

Good morning Bryan, So I managed to get the old fuel pressure regulator off and replaced it this morning. Bad news is that the problem still remains... So now I've been right through any possible fuel problems I guess your hunch is right and the problem is electronic. One thing I noticed is that the idle speed is way too high. Can I just adjust it with the screw without screwing up anything else? I'll let you know how I get on. Thanks again
Charlie

18Fiatsandcounting · Post by **18Fiatsandcounting** » Wed Sep 13, 2023 10:55 am

Idle speed adjustment on the FI cars is sometimes not obvious. It's not the throttle stop on the cable drum, towards the rear of the car. Instead, you need to find the air bleed screw which is on the opposite side (towards the front). You may need to find a picture online to see what I'm referring to.

Here's essentially how to do it:
Totally warm up the engine, and leave it running.
Adjust the throttle cable nuts so that there is some slack in the cable.
Turn in the air bleed screw all the way, but not too tight. The engine should falter but not die.
Adjust the throttle plate stop screw (with locknut) until the idle is just enough to keep the engine running, 600 rpm or so.
Then back out the air bleed screw until you get to the specified 850 rpm or so.

If your idle consistently runs really high, like 1500 or 2000 rpm, then that is a pretty good sign of an air leak on the intake manifold or the large air duct. With the engine running, move the various hoses connected to the intake system around, and see if it gets better or worse. that might give a clue as to where the air leak is (if there is one).

-Bryan

charlielucky · Post by **charlielucky** » Thu Sep 14, 2023 2:29 pm

Hi, thank you again for the advice.

I found an article on the Mirafiori database regarding the vacuum unit on the distributor. Apparently if this unit is faulty it could be the reason my engine is chocking at 3,500 rpm. I connected a tube to the top of my unit and tested it by sucking and blowing down the tube. Nada! There was no resistance either blowing or sucking. Does this mean the unit is faulty?

What do you think?

Regards

Charlie

18Fiatsandcounting · Post by **18Fiatsandcounting** » Thu Sep 14, 2023 10:19 pm

charlielucky wrote:I connected a tube to the top of my unit and tested it by sucking and blowing down the tube. Nada! There was no resistance either blowing or sucking. Does this mean the unit is faulty?

Hi Charlie, Yes, it is very common for these vacuum modules to fail, and based on what you described, it sound like yours has failed as well. Almost every original vacuum module that I've come across has a hole in the rubber diaphragm.

Replacement modules are available. As it happens, just today I rebuilt two vacuum modules by prying them apart and installing a new nitrile rubber diaphragm that I had to shape myself. While this seems to work, it is much easier to just pay $40 and buy a new module.

-Bryan

charlielucky · Post by **charlielucky** » Sat Sep 16, 2023 12:58 am

Hi Bryan,

I'm ordering a new vacuum unit for the distributor this week. Do I have to remove the distributor unit to replace the vacuum unit? I've never done this before so I was wondering how I make sure I don't screw up the timing. I don't have a timing gun but as far as I can tell the timing is pretty good at the moment.

Cheers
Charlie

18Fiatsandcounting · Post by **18Fiatsandcounting** » Sat Sep 16, 2023 6:09 pm

charlielucky wrote:Do I have to remove the distributor unit to replace the vacuum unit?

Yes. There are 3 screws holding the bracket for the vacuum unit to the base of the distributor, and they would be almost impossible to remove with the distributor still on the engine.

To prevent much change to your timing, mark the base of the distributor and the cambox hole where it fits into, with a small scribe mark. Also note very carefully which direction the rotor is pointing before removing the distributor. Line these back up when reinstalling the distributor, and you'll probably be pretty close. But you really should get a timing light. They're not that expensive.

There is some adjustment on the vacuum unit. You'll see a little plastic clip at the end of the shaft that comes out of the unit. The hole in the end of that should match up with the little ball pawl that is coming out of the base of the distributor, and this plastic piece clips onto that ball. You'll see how it works when you take the old one off. Make sure that the new unit is adjusted so that the plastic piece isn't pulling the pawl partially when it's reinstalled.

-Bryan

charlielucky · Post by **charlielucky** » Fri Sep 22, 2023 10:41 am

Hi, I need some more help please. As previously mentioned, my car starts to stutter and cut out from 3000rpm. I have replaced the following: New fuel tank, fuel pump, fuel filter, New injectors and fuel pressure regulator. I have checked the fuel pressure so I'm pretty sure the problem is not on the fuel line. I have changed the timing belt, Air filter and rubber hose unit that connects to the injection. I have replaced the vacuum unit on the distributor and checked that it is working correctly. I plan to borrow a timing gun this weekend to check the timing but I'm pretty sure this is not the problem. It seems to me that the ECU is getting the wrong signal from 3000 rpm but why is a mystery to me. Could it be a ECU problem? Is there a way to check the ECU? any other ideas?

Charles

18Fiatsandcounting · Post by **18Fiatsandcounting** » Sat Sep 23, 2023 10:39 am

Charlie, I'm running out of ideas, but my first thought would be to check the ignition timing as you mentioned. It should be 10 degrees BTDC (Before Top Dead Center) at idle, and more importantly, it should advance to about 35 degrees BTDC as you rev the engine up to 3500 rpm or so. If your centrifugal advance is not working as it should, the engine will idle fine but struggle to rev.

Another possibility is that the air vane in the air flow meter is sticking, or the electrical connections to it are poor.

Wish I had more to suggest...

-Bryan

charlielucky · Post by **charlielucky** » Sat Sep 23, 2023 11:11 am

Hi Bryan, Thanks for taking the time to reply. I'v borrowed a timing gun today so tomorrow I'll do my best to check the timing. I believe the idling rpm is supposed to be 850rpm. If the timing is off can I rotate the distributor a bit to compensate? Also I just received my new lightweight and more powerful starter motor. The problem is I can't get the old one off! I managed to get the bottom bolt out but the two top ones look impossible. For the moment I'm going to clean up the negative on the old one and wait till I can get the car up on a lift.

thanks again

Charlie

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