Engine Running rough and doesn't rev (well) beyond 3000-3500RPM - Alfa Romeo Bulletin Board & Forums
 
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post #1 of 14 (permalink) Old 10-11-2018, 07:14 AM Thread Starter
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Engine Running rough and doesn't rev (well) beyond 3000-3500RPM

Hey there

I recently opened a thread about my conversion to the electric fuel pump - this is not about that car.

So the title says it all the car (GTV2000 EU on Carbs) runs rough generally and I get heavy misfires beyond 3000-3500 rpm when driving on the road (2nd and 3rd gear). Take off is ok, car starts well and idles ok. The misfires also happen when the car is in neutral, but I'd say a little later, more like 3500-4000rpm. It think it gets worse when constantly try to accel a little. I think it gets better when I release the throttle for a little while. I use think here because its very hard to tell and its not a 100% consistent

We recently rerouted the fuel delivery to the firewall so it was clear to me that it must be a fueling issue (also because of the slight difference in where the misfires start to happen). Now I checked all the lines and fuel delivery seems very much ok. I had the pump, pump fuel into a container which sloshed out reasonably well (I unfortunately don't own a pressure gauge). I checked all the filters inline all very clean (and fairly new anyway). And I even reverted the setup to how it was before - no change either.

Next I was reading on the forums here and it seems to me that the symptoms sound also like bad condenser. Which would be the next thing to check for me but I have a hard time getting that into my head. Why would they go wrong when I make changes to the fueling?

Next would be carbs...

Any other ideas or cues?

Thanks a lot
Alessandro

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Last edited by AlessandroM; 10-11-2018 at 08:11 AM.
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post #2 of 14 (permalink) Old 10-11-2018, 08:05 AM
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Sometimes it‘s just bad luck without any reason....
After I mounted my refreshed cylinder head the alternator bearings were worn....
Changing the condenser is an easy try, maybe you are lucky
Did you check engine and ignition timing already?
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post #3 of 14 (permalink) Old 10-11-2018, 08:13 AM Thread Starter
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@mechtild

Not yet, I just checked whether the dizzie has come loose, but it hasn't.

Speaking of bad luck, the car has a lambda probe, but it stopped working a week before this issue appeared.

Learning, learning..
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post #4 of 14 (permalink) Old 10-11-2018, 08:39 AM
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It could be an ignition problem. Failing coils sometimes work OK at low rpm and light load but break down at higher rpm and higher load but anything else in the high voltage side can do it - distributor cap, rotor, plug wires, plugs.

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post #5 of 14 (permalink) Old 10-11-2018, 09:28 AM
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Having just gone thru my ignition system in some detail I have ignition on the mind. Not saying that IS your problem but sure worth checking. An adjustable timing light or even a plain old timing light is a very useful tool here. Not only can you verify static and full advance but you can see how regular the spark and advance is. If the light blinks irregularly at any RPM you can see you aren't getting good spark. If its impossible to see where the TDC pointer is aligning to or the alignment jumps around when the revs are stable or slowly rising, then the dizzy may have some slop in it. All those are good things to check regardless as the are adjustments that can easily go out from age of parts and loose clamp/bolt on dizzy itself.

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post #6 of 14 (permalink) Old 10-11-2018, 09:38 AM
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and... ignition parts are inexpensive / wear items. If it were me I'd throw a cap, rotor, condenser, points at it. Even (in the states) a good coil is less than forty bucks, nice set of wires the same. All in ~$125 for a nice tune up.

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post #7 of 14 (permalink) Old 10-11-2018, 10:44 AM Thread Starter
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Thanks guys - I will investigate a little more into the dizzy then.

By the way I also tested the fuel tank for vacuum - there was none.

Learning, learning..
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post #8 of 14 (permalink) Old 10-11-2018, 12:34 PM
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An even cheaper test of the ignition is to run the engine at night with the hood open, and look for sparks. Bad wires will look like a lightning storm when it is dark.

Another possible idea: since the problem started after re-routing the fuel plumbing, is it possible that some debris was shaken loose and is now clogging the carburetors? Say the float needle valve(s), or the main jet(s)?

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post #9 of 14 (permalink) Old 10-11-2018, 11:00 PM Thread Starter
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Another weird thing is that the spark plugs are almost sealed into the head. I needed a lot of initial force to remove them (needed a long wrench). Looking at the threads of the removed ones they look brand new. The new ones that I turned in needed very little force on the other hand just as I am used to. So weird.

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post #10 of 14 (permalink) Old 10-11-2018, 11:04 PM Thread Starter
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Quote:
Originally Posted by Alfajay View Post
An even cheaper test of the ignition is to run the engine at night with the hood open, and look for sparks. Bad wires will look like a lightning storm when it is dark.

Another possible idea: since the problem started after re-routing the fuel plumbing, is it possible that some debris was shaken loose and is now clogging the carburetors? Say the float needle valve(s), or the main jet(s)?

The leads are one year old and of the more expensive type (the blue ones from AH) I see no sparking/sparks in the dark.

I will try to the check the carbs for any cloggedness. It's just weird, wouldn't I notice this more if only some jets were clogged? The float needle valve on the other hand. Will check thoroughly.

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post #11 of 14 (permalink) Old 10-12-2018, 02:00 AM
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do you have a fuel filter- pressure regulator installed?
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post #12 of 14 (permalink) Old 10-12-2018, 04:37 AM Thread Starter
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hey @quadrifolio

Yeah the original Fispa-thing with the diaphragm. I tried swapping it out for a disc type regulator, no change - as lumpy as.

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post #13 of 14 (permalink) Old 10-14-2018, 12:59 AM Thread Starter
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So the car seems to be working fine again.

We changed the fuel pump first - no change (to be expected..). My static Timing light didn't show any sort of weird behaviour. I was then able to borrow a friends lambda probe which quickly revealed that the mixture that was burned was alright (no leaning out). So it had to be the ignition. I had a spare old Bosch Blue Coil and we took another friends condenser and it worked just fine. I cannot tell what it was but it almost seems like it runs better than it did the last few month which sounds lot like something was broken before and just severed to the point where the car stopped running whatsoever. Then again very much bad luck with the timing.

By the way the timing light revealed no problems whatsoever...

I would totally go for a 123 Tune if i wasnt planning a TS/EFI Setup in the nearer future.

Thanks for all the help!
Alessandro

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Last edited by AlessandroM; 10-14-2018 at 01:01 AM.
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post #14 of 14 (permalink) Old 10-14-2018, 09:35 AM
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It's always good when you have the courtesy to tell the results after a malfunction so we all can learn...thanks
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