Stumble and miss in my '80

cyclemichael · Post by **cyclemichael** » Mon Jun 09, 2014 12:59 am

Hello everyone,
I've been having problems with stumbling and a miss in the engine. It starts once the car has been going for a few minutes and is warmed up. It doesn't happen when i have my foot off the the pedal, but cruising and acceleration are a problem. It can get pretty bad. Almost scary when it really misses speeding up.
I just finished taking out a leaking fuel injector, and replacing all the hoses, so I am pretty confident that's not it. I am looking for advice on what top look at next. The car does tend to idle high/weird (it jumps a little). When i tried turning down the idle, it just stalls, and turning it up doesn't have any effect on the stumble. Could it be my mixture? The car does backfire a little, and feels like it could be lean. How can I check if my mixture is good? I know where the screws are but don't want to just fumble around with them.
Any ideas on how to fix my miss and sporadic RPMs would be greatly appreciated!

Thank You!
Michael

ORFORD2004 · Post by **ORFORD2004** » Mon Jun 09, 2014 1:12 am

If you can try AFM from another car or you can clean the track of the AFM and apply WD40 after that

RRoller123 · Post by **RRoller123** » Mon Jun 09, 2014 9:19 am

Check the AFM door flap for full free motion, no sticking whatsoever. It can be repaired or slightly sanded to free it up. There is a thread here on the forum about how to adjust the internal arm so that it will track onto fresh TFM material. This has stopped stumbling on many a car, mine included. It is a lot easier to do than it looks. (Don't apply any lubricant to the track, it reads by resistance and must be clean)

ORFORD2004 · Post by **ORFORD2004** » Mon Jun 09, 2014 1:08 pm

(Don't apply any lubricant to the track, it reads by resistance and must be clean

The WD40 trick was from a friend in recording industry and he use it when he get static noise on slider.

cyclemichael · Post by **cyclemichael** » Mon Jun 09, 2014 9:51 pm

I am kinda new to mechanics and so some of this vocabulary is escaping me. AFM stands for Air Flow Meter correct? And is this not the same thing as my air flow sensor? The aluminium door in the housing on top of the air filter rotates just fine. No blockages, everything is clean (finally something the PO did right!). The actual filter looks clean as well, if that matters. What is a TFM?

Where should I start looking next for my stumble, if what I have done was what you were indeed talking about?

RRoller123 · Post by **RRoller123** » Tue Jun 10, 2014 6:11 am

TFM is thick film resistive material, which is what the AFM (yes, this is the same as the air flow whatever) uses to measure air mass for the FI system. It is located under the black plastic top cover on the unit.

cyclemichael · Post by **cyclemichael** » Tue Jun 10, 2014 6:48 pm

Oh okay I was just looking in the aluminum housing, I didn't look under the black cap. I will tomorrow on my day off. Also planning to gap some spark plugs and see what condition they are in.

This is kind of unrelated but I am having trouble setting my idle. It seems to be not in the right spot when I am idling but under acceleration/cruising/everything else it seems fine. If I seat the idle screw completely (as instructed in Brad Artigue's article) my engine will stall. I have tried a few different ways ( using the linkage stop to keep gas flowing) but nothing seems to work. Could this have to do with the air bypass(?) on the air filter?

Thanks!

Michael.

cyclemichael · Post by **cyclemichael** » Wed Jun 11, 2014 2:21 pm

I have a another question as well. Should the black cap on the AFM be sealed in with some kind of adhesive? because it is right now and I don't want to mess around with it if its supposed to be sealed.
Thanks,
Michael

RRoller123 · Post by **RRoller123** » Wed Jun 11, 2014 8:01 pm

Yes if you pull it to work inside, it needs to be sealed up to stay absolutely clean afterwards.

divace73 · Post by **divace73** » Wed Jun 11, 2014 8:13 pm

have a read for Brad's fuel injection pdf, it's a document that is invaluable. http://www.artigue.com/fiatcontent/Arti ... 124_MM.pdf
If you follow his steps you will find the source of your issues.

cyclemichael · Post by **cyclemichael** » Fri Jun 13, 2014 2:47 am

So I went to my mechanic to pick his brain. We went for a little ride and he adjusted my timing. Runs much smoother now, though still with it's fair share of hiccups. Im going in tomorrow to get my timing adjusted (I don't own a timing light) and to have the AFM bypass adjusted since I was not aware how sensitive that was, or how big of a difference it could make. I essentially was turning it until something felt better. (Brad Artigue called it an "easy adjustment)

As for the black AFM box, if there are still some issues the black AFM box will be next, along with plugs (i keep meaning to do them but it just hasn't happened yet.

I had read Brad Artigue's article but i gave it a more thorough read through again. It helped me to better understand how the car works and allows me diagnose some problems easier.

Thank you all for the help. Ill update after the mechanic tomorrow.

cyclemichael · Post by **cyclemichael** » Sun Jun 15, 2014 12:55 am

Mechanic adjusted the MAF meter and Timing. Runs stronger, but still with a stumble/lurch. At least I know that it's not those things anymore, and I can chase it down one area at a time. But for now... replacing a fuel line a broke being an idiot. Fun times!

narfire · Post by **narfire** » Sun Jun 15, 2014 1:13 pm

Have you checked for any air entering the system after the AFM? The plastic/rubber boot can crack, the hose clamps bit loose, the hoses to and from the aux air valve, the bolts loose on the intake plenum and my problem was a tear/hole in my brake booster. I could never adjust the idle to where it was supposed to be until I changed the leaking booster. I have better brakes as well now. Stick your head under the steering wheel when the engine is running and press the brake pedal....hissing noise? if so the thing has a leak.
You'll find it....eventually.
Chris

speedracer · Post by **speedracer** » Sun Jun 15, 2014 8:57 pm

Change your fuel filter.

I just change mine because of a hiccup and stumble when I was accelerating, and it did the trick. My Spider is a carb model, but I'm sure it will help an FI engine as well. I always keep an extra one on hand because I've had this problem before and it worked then as well. It seems like I change the filter on my Spider far more often than I do with my other cars, I'm guessing because the car sits more and the tank probably has more crap and rust in it than the others.

Anyway, they're cheap enough and they should be changed if you don't know the last time it was done...

cyclemichael · Post by **cyclemichael** » Mon Jun 16, 2014 2:53 pm

I am pretty sure I checked all the hoses and clamps for tightness/leaking, but it can never hurt to double check them all! I still have yet to actually open up the AFM black box, so it could still be that. Haven't checked the plenum though. Ill check my brake booster, although I don't hear any hissing from the brake when I engaged it, but then again I'm not listening for it.
I'll look into replacing the fuel filter. It probably is pretty old. My car doesn't sit much now, but I can't speak for the two POs.
I broke a fuel line so I've got to replace that section today.

Thanks you all!

Stumble and miss in my '80

Stumble and miss in my '80

Re: Stumble and miss in my '80

Re: Stumble and miss in my '80

Re: Stumble and miss in my '80

Re: Stumble and miss in my '80

Re: Stumble and miss in my '80

Re: Stumble and miss in my '80

Re: Stumble and miss in my '80

Re: Stumble and miss in my '80

Re: Stumble and miss in my '80

Re: Stumble and miss in my '80

Re: Stumble and miss in my '80

Re: Stumble and miss in my '80

Re: Stumble and miss in my '80

Re: Stumble and miss in my '80