Alfa Romeo Forums banner

1 - 20 of 35 Posts

·
Registered
Joined
·
66 Posts
Discussion Starter #1
I've been chasing problems on a 3.0 Milano for a few years. I'm closer than ever, which makes it all the more frustrating that each time I seem to fix a problem, the car runs worse.

Some background: 2020 is the year

The latest:
For the better part of a year, the car has ran pretty good cold, and stops producing power when hot. The change is immediate (not gradual at all) that happens the second the fan kicks on. If it's not under load, the condition manifests as a slower climb in the rev range (a stumble, maybe). Under load, the car becomes undrivable. Slowly slipping the clutch and being very gently on the throttle is usually enough to limp it home. There are spurts where it feel like it wants to go, but they are intermittent and the exception to the condition.

I had long suspected fuel pressure as a culprit, so I plumbed a gauge in-line near the 7th injector and confirmed that fuel pressure wasn't great. To take care of that, I did a bunch of fuel work.

In the last month, the car has received:
  • a newly cleaned/flushed tank
  • new fuel pressure regulator
  • all soft fuel lines have been replaced with new 7mm fuel line
  • new filter, strainer, and additional strainer (in-line just before the pump), and pump
Fuel pressure seems to be sorted, at around 25 PSI at idle and about 38 on the throttle. System holds about 22 PSI with the engine off.

As mentioned, the car had been running GREAT when cold. Starts were quick and without issue. No hesitation when coming off throttle, no power loss, etc. I could cruise around the neighborhood without issue until it got into a fully hot condition.

In my quest to chase the hot problems, I pulled the fuel vapor canister today to check and replace the vacuum lines. All other vacuum lines have been previously replaced with a silicon kit from Greg Gordon. So now all vacuum lines under the hood are replaced. There was a split connector to the small outlet on top of the vapor canister, so I was hopeful I had found the problem.

However;

The car runs significantly WORSE after that line change. Hot problems still exist, except now hot idle is at roughly 500 RPM with the idle adjustment nut at the plenum all the way out. Talk about discouraging.

I'm convinced the problem is a lean condition when hot. The idle adjustment is VERY responsive when cold, but seems to make almost no difference when hot (with the exception being the car dies if I adjust the nut in any further than "barely making contact with the o-ring"). The car will die unless static timing is set to around +14 (doesn't seem right), at which point it idles low, but does seem responsive when manipulating the throttle by hand. Setting the static timing closer to stock +7 results in an extremely lumpy idle and the occasional backfire wit the throttle coming off idle.

What I've tried:

  • pulled the seventh injector Bosch connector to ensure no overly rich condition. No change.
  • tightened the small lead coming off the positive battery terminal.
  • ensured idle adjustment o-ring is functioning well. I have replaced this no less than 3 times in the last year.
  • checked AAV functionality. fully closed when hot, and open when room temp.
I haven't ruled out the possibility of a vacuum leak, but I am absolutely at a loss of where it could be coming from. Every hose routed off the big air intake and plenum are new silicon, the big air intake hose is new, plenum coupler hoses are new. All clamps are double checked for tightness. When the hot condition begins, I think I'm hearing a high-pitched air intake sound coming from somewhere around the plenum. Trying to isolate it has not been successful so far.

Any ideas? I feel like the close I get, the farther away I end up.
 

·
Premium Member
1984 GTV6, 1973 Berlina, 1987 Milano
Joined
·
1,566 Posts
Have you tried disconnecting the battery to clear out the stored fuel trim in the ECU?

I would also try unplugging the O2 sensor and see how it runs open loop. If it runs better replace the o2 sensor.

Sent from my GM1917 using Tapatalk
 

·
Premium Member
Joined
·
15,861 Posts
Have you tried driving the car with the gas cap removed, to change the pressure in the tank? Fuel pressure dropping after a while when driving due to improper system venting?

Also, you mention: "The change is immediate (not gradual at all) that happens the second the fan kicks on"

That's different. Sounds like an electrical problem. Fuel problems usually occur over a period of time, not suddenly, unless the pump quits.

So which is it? Gradual change or sudden?
 

·
Premium Member
1984 GTV6, 1973 Berlina, 1987 Milano
Joined
·
1,566 Posts
One other thought. My GTV6 would stumble when accelerating right after I bought it. The big air hose was shifting at the MAF sensor causing it to go lean and fall on its face.

I'm in Portland and have some spare 2.5 parts if you need to borrow anything to swap parts without buying them.

Sent from my GM1917 using Tapatalk
 

·
Registered
Joined
·
66 Posts
Discussion Starter #5
Have you tried disconnecting the battery to clear out the stored fuel trim in the ECU?

I would also try unplugging the O2 sensor and see how it runs open loop. If it runs better replace the o2 sensor.

Sent from my GM1917 using Tapatalk
Re: battery unplugging. Yes, I store the car with the battery leads disconnected and the battery on a float charger. It gets disconnected after every working session.

Re: O2 sensor. I need to try this again. Before fixing the vapor canister line (when the car was running best), I did pulling the O2 sensor while idling and it seemed to negatively impact the idle. FWIW, the O2 sensor was replaced new last year when the new exhaust went on.
 

·
Registered
Joined
·
66 Posts
Discussion Starter #6
Have you tried driving the car with the gas cap removed, to change the pressure in the tank? Fuel pressure dropping after a while when driving due to improper system venting?

Also, you mention: "The change is immediate (not gradual at all) that happens the second the fan kicks on"

That's different. Sounds like an electrical problem. Fuel problems usually occur over a period of time, not suddenly, unless the pump quits.

So which is it? Gradual change or sudden?
Very sudden change. Not gradual. I agree with the symptoms seeming electrical in nature. I've replaced the CTS, TTS, plug wires, distributor (used part), plugs, double relay, in an attempt to solve what I originally thought was an electrical issue.
 

·
Premium Member
Joined
·
15,861 Posts
I see. Does it do it exactly when you think the fan starts? Have you wondered if there is some connection there? Try disconnecting the fan for a drive to see what happens when the engine warms up, but not before it overheats?
 

·
Registered
Joined
·
359 Posts
I would double check the silicone hoses. Problem is, they Do crack but are very hard to detect. Typically hairline cracking around the circumference close to a clamp connection (but not always) or where they are subjected to high heat. Just a thought.....sure sounds like a leak to me
 

·
Registered
Joined
·
66 Posts
Discussion Starter #9
I would double check the silicone hoses. Problem is, they Do crack but are very hard to detect. Typically hairline cracking around the circumference close to a clamp connection (but not always) or where they are subjected to high heat. Just a thought.....sure sounds like a leak to me
You're on to something here. I built and ran a low-pressure smoke machine into the big air hose today and sure enough, smoke slowly emerged from under the plenum, somewhere around the front passenger side of the engine. I need to try to get a closer look tomorrow, but it appears in the area of either cylinder 1, 2, or 4.

Injectors and seals were new when I put the engine back in a few years ago, however, I had a pretty nasty backfire when I was doing some distributor work about a year ago. Could a large enough backfire cause one to unseat or become damaged?

Another potential source could be the intake couplers, but I'm fairly confident those are good. All new rubber and clamps tightened a few days ago when I was putting everything back together.

That leaves only the intake manifold gaskets, which I can't really remember if I replaced or not when I pulled the engine.

Regardless, I'm going to see if I can pinpoint the source of the leak tomorrow. In a way, it's reassuring that the cause is exactly as the symptoms would suggest.
 

·
Registered
Joined
·
66 Posts
Discussion Starter #10
Update: smoke machine revealed a small leak at the throttle body gasket. Tightened the connecting nuts down and couldn't detect any additional leakage from that area. Also tightened the clamp on the AAV connecting hose at the back of the plenum, just incase.

Cold performance is back to where it was - pretty good. Hot performance is exactly the same, with a very low, lumpy idle.

BUT. I was able to isolate exactly WHEN the "hot condition" begins. Pinching the hose between the plenum and AAV when cold killed the engine (as expected). It's when the AAV closes that the "hot condition" starts and the engine does not run properly.

One change now that the throttle body vacuum leak is mitigated seems to be a backfiring on throttle when hot. I'm pretty sure the timing is still very advanced, so I may try to dial that back to static +7 to see if that helps. It's difficult to adjust when idle is so rough.

Do you think the backfiring on throttle indicates a rich condition now when hot? I had not experienced that before the smoke tests and fixes.

Del, I pulled the fuel cap when the hot condition started and there was no difference. I think fuel is good. Pressure isn't dropping at all when these symptoms start.
 

·
But Mad North-Northwest
Joined
·
10,505 Posts
I'd suggest going through the whole L-jetronic troubleshooting guide from start to finish.


A few things come to mind as potential causes like a bad CTS or maybe a bad or misadjusted TPS. Those are both easy to check so maybe start there. After that, see if the low/lumpy hot idle respond at all to the idle air bypass adjustment at all.

But really you should go systematically through the guide.
 

·
Registered
Joined
·
66 Posts
Discussion Starter #12
Thanks Gubi. I've been through the entire guide about 3 times in the last few years. I'm confident in all the electrical pieces. TTS, CTS are new. TPS clicks at the correct time.

I don't mind going through the guide again, but I'm skeptical anything had degraded since last time, which was last week.
 

·
But Mad North-Northwest
Joined
·
10,505 Posts
Okay, reading comprehension on my part, sorry. I would check both the CTS and TPS with a multimeter if you haven't. I had one TPS that clicked fine but didn't actually close the circuit at idle.
 

·
Registered
Joined
·
359 Posts
Good Luck! As a general rule, the silicone hoses should be replaced every 2-3 years.(not a fan) The problem with them is they get very brittle but because they hold shape extremely well, it's nearly impossible to find a leak. They get small fractures in them particularly in bends and anywhere they are exposed to higher heat (including summer) and almost always where they are clamped tightly.
 

·
But Mad North-Northwest
Joined
·
10,505 Posts
Good Luck! As a general rule, the silicone hoses should be replaced every 2-3 years.(not a fan) The problem with them is they get very brittle but because they hold shape extremely well, it's nearly impossible to find a leak. They get small fractures in them particularly in bends and anywhere they are exposed to higher heat (including summer) and almost always where they are clamped tightly.
I don't know what silicone hoses you've used, but that doesn't sound accurate at all for vacuum hoses. The silicone hoses I had on my Milano (from Greg Gordon) were in perfect condition 8 years after I installed them, and I suspect they are still in great shape with the new owner five years later. They weren't brittle or cracked at all, still perfectly rubbery and flexible. Most of them did not even require clamps.
 

·
Premium Member
Joined
·
15,861 Posts
You may be one to something, but I still find it odd that you feel that the problem basically starts immediately when the fan comes on. Or, is it just apparently a coincidence that the problem raises it's ugly head around when the fan comes on when the engine temperature reads a certain value on the gauge?
 

·
Registered
Joined
·
66 Posts
Discussion Starter #17
Okay, reading comprehension on my part, sorry. I would check both the CTS and TPS with a multimeter if you haven't. I had one TPS that clicked fine but didn't actually close the circuit at idle.
Findings:

TPS measures correctly with throttle closed, but is stuck on an open circuit (infinite resistance I think this implies open, but I'm not great with electricity) with the throttle open. So that was unexpected and probably causing other issues, but seems to absolve itself from idle troubles. I could be wrong though.

CTS: I had an extra that measured good, which I'm going to swap in tomorrow. I'm fairly confident the on the car is good, as I measured it before I put it on. I'll still swap to have an updated, known-good unit.
 

·
Registered
Joined
·
66 Posts
Discussion Starter #18
You may be one to something, but I still find it odd that you feel that the problem basically starts immediately when the fan comes on. Or, is it just apparently a coincidence that the problem raises it's ugly head around when the fan comes on when the engine temperature reads a certain value on the gauge?
That's kind of my suspicion. My theory is that whatever condition tells the ECU to trigger the fan circuit also changes something with the ignition system. Maybe injector duration (which I believe the TPS controls). I have no proof of this though, and would welcome any education.
 

·
Registered
Joined
·
359 Posts
I don't know what silicone hoses you've used, but that doesn't sound accurate at all for vacuum hoses. The silicone hoses I had on my Milano (from Greg Gordon) were in perfect condition 8 years after I installed them, and I suspect they are still in great shape with the new owner five years later. They weren't brittle or cracked at all, still perfectly rubbery and flexible. Most of them did not even require clamps.
I too had the same hoses 2x and had problems both times. Maybe I had a bad batch?
 

·
But Mad North-Northwest
Joined
·
10,505 Posts
The fans are a separate system. They aren't triggered by the ECU and don't interact with it directly. If the problem is only happening when the fans are on, maaaaaybe the fans are pulling enough amps that the voltage to the ECU is dropping, I suppose? But if it's always happening hot regardless of whether the fans are running or not then it's likely nothing to do with the fans.
 
1 - 20 of 35 Posts
Top