Technical really stubborn multi air bleed or failed multi air?

[beebe101]

ill see if i can get my borescope in to check the valves
from the leakdown test it downst have any valves

 

[beebe101]

well plot twist my intake valves are opening so my multi air brick is functioning still not sure what would cause that, gonna go through and check my timing but i dont think its timing because i used the lockout tools and im not getting a correlation error

 

[Mike1alike]

That is good news!
It means the problem is the head gasket. It is the one that blew on the high revving. Makes sense! That's why there's no compression.

 

[bugsymike]

That is good news!
It means the problem is the head gasket. It is the one that blew on the high revving. Makes sense! That's why there's no compression.

Fingers crossed, but strange on all cylinders.

 

[Mike1alike]

It is a little bit strange but not impossible. After all analysis now I'm sure that that's it, blown HG gasket. I might be wrong, of course.
We all kind of jumped to the multiari red herring first. Good thing it was borescoped and looks ok. You @bugsymike were kind of the most realistic, you didn't think there is anything wrong with the multiair, just let yourself convinced by the discussion in the end.

Now, I'm thinking of an easy test to make sure it's the gasket. I think this could work: getting the spark plugs out, borescope (if you want cause you have it, but it should work even without borescope) in one cylinder and blowing smoke in other cylinder.

 

[beebe101]

I'm not sure if it's the head gasket or timing, because wouldn't a head gasket failure show up on a leakdown test? This could have happened when i was doing the oil pump so ill cheak timing first because thats the easiest. If it's not that, what I'll do is remove the cam so all the valves are closed, then hook my compression tester up to one cylinder, my leakdown tester to another cylinder, and plug the last two to see if there's any cross compression. I've never had a head gasket fail like this, but I'd take a head gasket problem over a bad MultiAir system. It also backfired out of the intake, and I'll see about posting the video.

 

[beebe101]

 

[Zardo]

yea even without the air brick in the compression reading was 0

I don't really understand how you got 0 psi on a compression test, on all cylinders. Is this a digital tester with an A/D converter? Is it a classic analog tester which needs a manuel reset of the needle after each test? Did you reset the compression tester before cranking?

To me, 0 psi sounds totally unplausible. The standard atmospheric pressure is 14.696 psi. .

Even with leaky intake and exhaust valves, you should get some value of 0.xxx psi relative to ambiant pressure, therefore not equal to zero, right?

Discussion of compressions tests rule of thumb with an AI:

"What about the U.S. version of the turbocharged Fiat abarth 500 multiair which has a compression ratio of 9.8?"

ChatGPT:​

For the U.S. Fiat 500 Abarth 1.4L MultiAir Turbo (9.8:1 static CR), the 17–20× rule does NOT apply, and the expected compression numbers are lower than that rule of thumb would predict. Here’s why and what the real numbers should look like:

Why turbo MultiAir engines don’t follow the 17–20× rule​

The 1.4L MultiAir engine is very different from a traditional naturally-aspirated camshaft engine:

1. MultiAir uses electro-hydraulic variable valve timing & lift​

• The intake valves are not mechanically tied to the camshaft duration.
• Under cranking, the ECU uses a reduced valve lift strategy to improve starting, NOT the full high-lift profile.
• This dramatically changes the effective (dynamic) compression ratio during cranking.

2. Turbocharged engines are tuned for low cranking compression​

To avoid knock under boost, turbo engines sacrifice dynamic compression at low rpm by using:

• Later intake valve closing
• Lower valve lift at cranking
• Valve overlap control

Even with the same static CR, turbo engines typically show lower cranking PSI than NA engines.

3. Factory spec from Fiat/Chrysler (Service Manual)​

Fiat’s published compression test spec for the 1.4 MultiAir Turbo is:

➤ Minimum: ~130–135 psi​

➤ Typical healthy: 150–170 psi​

➤ Max variation between cylinders: 7–10%​

So a healthy engine may show, for example:

• 155
• 160
• 165
• 162

And that is perfectly normal.

---

What you should expect on a good engine​

For a healthy U.S. Fiat 500 Abarth 1.4 MultiAir Turbo:

Normal range: 150–170 psi​

Acceptable minimum: 130–135 psi​

Important: cylinders must be within ~10% of each other​

Readings above ~180 psi are uncommon but not impossible on a warm engine with a strong battery.

"does the throttle body of the Fiat 500 multiair need to be set to fully open in order to do the compression test?"

ChatGPT:​

Short answer: Yes — for the most accurate compression reading, the throttle should be held fully open.
But on the Fiat 500 MultiAir, there are some important details specific to this engine.

---

Does the throttle need to be wide open?​

Yes.
Just like most modern engines, you get the most accurate compression numbers when the throttle plate is fully open during the test.
Why?

• It eliminates intake restriction
• Allows maximum airflow into the cylinder
• Gives the highest and most consistent cranking PSI readings

If the throttle stays closed, readings may drop 10–30 psi, depending on battery strength and starter speed.

---

BUT — the 500 MultiAir is drive-by-wire (no cable), so…​

The throttle won’t open just because you push the accelerator pedal during cranking.
Most drive-by-wire systems (including the Fiat 1.4 MultiAir) disable throttle movement during crank mode unless the ECU is in a special state.
So pressing the pedal does nothing for opening the throttle during a normal compression test.

---

Best method for a proper WOT (Wide Open Throttle) compression test on the 500 Abarth / MultiAir​

Choose one of these:

Method 1 — Use “clear flood” mode​

Most FCA/Fiat ECUs recognize wide-open throttle before cranking as a “clear flood” signal.
Steps:

1. Key ON (not start)
2. Floor the accelerator (hold WOT)
3. Crank the engine

→ In clear-flood mode, the ECU disables fuel AND fully opens the throttle body.
This is usually the easiest and safest method.

---

Method 2 — Manually command throttle open with a scan tool​

Tools like:

• AlfaOBD
• MultiECUScan
• Snap-On MODIS/SOLUS

…can issue a “throttle open” command or run an actuator test.
This gives guaranteed WOT.

---

Method 3 — Remove the intake tube and prop the throttle open​

Only if necessary.

• Key OFF
• Remove intake tube
• Gently push the throttle plate open with a soft plastic tool
• Do NOT force the plate; it’s motor-driven and fragile

I only recommend this if the ECU method cannot be used.

---

Practical note​

Even if the throttle isn’t perfectly wide open, the MultiAir engine will still produce usable readings — but they may be lower than expected.
For accurate results:

✔ Engine warm​

✔ Fully charged battery
✔ Fuel disabled (WOT or fuse removal)
✔ Spark disabled (unplug coils)
✔ All plugs removed
✔ Throttle fully open

---

If you want, I can give you:​

• The correct compression spec for your exact model/year
• How to interpret uneven readings
• How to do a proper leak-down test on the MultiAir engine

Just tell me what numbers you measured.

 

[beebe101]

I’ll double-check today. The last time I checked was before replacing the oil pump, so at that point it could have been that the brick was in safe mode because of the cam code. But it still sounds like zero compression when cranked. It was the normal style compression tester, and it was good because I used it to check compression on another car successfully.

 

[Mike1alike]

To me, 0 psi sounds totally unplausible. The standard atmospheric pressure is 14.696 psi. .

Even with leaky intake and exhaust valves, you should get some value of 0.xxx psi relative to ambiant pressure, therefore not equal to zero, right?

That logic is cute, but I don't think it goes like that really.
If it would, when you'd hook up the tester, the needle would jump to the atmospheric pressure number, wouldn't it?!

It's very intriguing this problem, this topic here. It was from the beginning but somehow I feel like I've grown into it, I'm more and more interested. "What's going on..." "What's happening there..."
@beebe101, I I can't wait for you to find out what's going on...!

 

[beebe101]

ill definitely keep updating, i checked compression again and it was 0 again

 

[Zardo]

That logic is cute, but I don't think it goes like that really.
If it would, when you'd hook up the tester, the needle would jump to the atmospheric pressure number, wouldn't it?!

In order for a gas to flow out of the cylinder, it must overcome the flow resistance of an open valve and it must displace the outside air. Therefore, the pressure of the trapped gas inside the cylinder must be higher than the ambiant pressure outside. Only a tiny pressure differential might be needed when cranking at 300 RPM, but this differential cannot be strictly zero. Maybe the tester isn't very accurate, otherwise it should at least show a tiny move of the needle.

The needle doesn't jump to atmospheric pressure since usually those testers only measure a pressure differential relative to ambiant pressure (or whatever pressure it was set to when resetting the needle) - therefore it goes to zero when it's resetted and the valves are open and the piston isn't moving

However, in practical use, things might be different: I did compression testing once on a homebuild aircraft featuring a 2 l piston engine, the tester was actually rather inaccurate, it would go to 200 psi by a 180° turn of the needle, and the needle wouldn't even budge if the cranking speed was very low. We would hand-prop that engine with all the spark plugs removed.

 

[bugsymike]

I'm not sure if it's the head gasket or timing, because wouldn't a head gasket failure show up on a leakdown test? This could have happened when i was doing the oil pump so ill cheak timing first because thats the easiest. If it's not that, what I'll do is remove the cam so all the valves are closed, then hook my compression tester up to one cylinder, my leakdown tester to another cylinder, and plug the last two to see if there's any cross compression. I've never had a head gasket fail like this, but I'd take a head gasket problem over a bad MultiAir system. It also backfired out of the intake, and I'll see about posting the video.

Backfiring out of an intake usually points to damaged valves stuck open.
Surely when leak test done air would have blown out somewhere to locate loss, inlet manifold, if head gasket then either in to radiator coolant tank with lid off or back out of another adjacent plug hole as you mention.
No sign of cam damage? I know on some engines these days the cam lobes are pressed on and can move on shaft (2.0 litre Fiat Scudo with Peugeot engine for one)

 

[beebe101]

That’s why I’m thinking it’s timing. It’s weird—I could have also connected my coils to the wrong connectors. The cam looked to be in good condition. I don’t think it’s bent valves, because there would be marks on the pistons from collisions. I still have a long way to go, but this is a step in the right direction.

 

[Mike1alike]

Surely when leak test done air would have blown out somewhere to locate loss, inlet manifold, if head gasket then either in to radiator coolant tank with lid off or back out of another adjacent plug hole as you mention.

I was rather thinking the head gasket blew just between cylinders there. That is a narrow space, narrow piece of gasket there and with high pressure on the both sides between cylinders (from high revved) it just blew between all of them. That's why no compression and when testing air goes from one to another and intake/outtake manifold. That's why the backfire too. That makes sense to me and I put it down as high possibility.

 

[beebe101]

I was rather thinking the head gasket blew just between cylinders there. That is a narrow space, narrow piece of gasket there and with high pressure on the both sides between cylinders (from high revved) it just blew between all of them. That's why no compression and when testing air goes from one to another and intake/outtake manifold. That's why the backfire too. That makes sense to me and I put it down as high possibility.

yea im definitely not ruling it out just going from easiest to hardest to check also i dont know if i mentioned but the car only has about 112k on it