[nverb]

I have a 2004 325xi, M54 2.5L.

I'm having an intermittent misfire on cylinder 3 with SES light. This misfire only occurs when driving uphill. If I shut the car off and turn it back on the SES light goes away and the car will run fine. Even if I drive uphill it might run fine, other times it might not.

So far I've changed all spark plugs and the coil in cylinder 3. Also put a new valve cover gasket and DISA valve on. Ran compression test in all cylinders and got these.

1. 135
2. 140
3. 140
4. 139
5. 140
6. 120

I swapped fuel injector from cylinder 3 with 2. Disconnected fuel injector harness to measure internal resistance, installed noid light to test injector pulse, load test ignition coil driver circuits. I did an adaptive memory reset and the car ran good for 1.5 days then misfire returned.

Anyone have suggestions on what to look for next and how to fix?

 

[Bali]

Read engine fault codes.
Check fuel managment health by looking at the important PIDs at hot idle.
Read through this misfire guide.

• Fuel trims, lean codes, misfires, and how to diagnose

 

[nverb]

Read engine fault codes.
Check fuel managment health by looking at the important PIDs at hot idle.
Read through this misfire guide.

• Fuel trims, lean codes, misfires, and how to diagnose

Thanks, Bali. I read this and is very helpful.

I haven't received any fuel trim codes like, P1071/P0174. Only the P0303. Also, I have a 41psi prime pulse at the fuel rail. Do you think a bad fuel pump and/or fuel filter would cause the problem I'm having?

 

[cigma2312]

Thanks, Bali. I read this and is very helpful.

I haven't received any fuel trim codes like, P1071/P0174. Only the P0303. Also, I have a 41psi prime pulse at the fuel rail. Do you think a bad fuel pump and/or fuel filter would cause the problem I'm having?

Spec should be 50 psi so it could be foreshadowing a potential fuel pump failure. Also check the fuel filter, that could cause an issue with fuel pressures too.

 

[nverb]

Spec should be 50 psi so it could be foreshadowing a potential fuel pump failure. Also check the fuel filter, that could cause an issue with fuel pressures too.

Thanks, cigma2312. Do you think a bad fuel pump or fuel filter would cause the P0303?

 

[Bali]

a bad fuel pump or fuel filter would cause the P0303?

Many different things can cause a misfire. You need to first look at the fuel management system to see if anything is out of balance. That’s why I asked for the important PIDs at hot idle.

• Short term fuel trim bank 1
• Long term fuel trim bank 1
• Short term fuel trim bank 2
• Long term fuel trim bank 2
• MAF value in g/s
• Coolant temperature in C
• RPM

 

[nverb]

Thanks, Bali. Here's what I'm reading at a hot idle:

• Short term fuel trim bank 1: Fluctuates between 0.8—5.5%
• Long term fuel trim bank 1: 0.0 %
• Short term fuel trim bank 2: Fluctuates between -3.9—0.8%
• Long term fuel trim bank 2: 0.0%
• MAF value in g/s: 3.78 g/s
• Coolant temperature in C: 73°
• RPM: 695-706

Does anything look out of wack?

 

[Bali]

• Coolant temperature in C: 73°C
Does anything look out of wack?

Engine is not fully up to operating temperature. It should be at least 94 C.

I would do a cold start log and see what the coolant temperature profile is. Thermostat may be opening too low.

 

[nverb]

Thanks Bali.

I’ll start a cold log in the morning and I’ll redo the hot after I drive the car around. The log above was taken after the car ran in park for 20 minutes, might not have been an accurate temp.

Could the coolent temp/thermostat cause the misfire?

 

[Bali]

Could the coolent temp/thermostat cause the misfire?

Unbalanced fuel management can cause a misfire.

 

[nverb]

Unbalanced fuel management can cause a misfire.

Thanks Bali. Could a cooler running engine cause unbalanced fuel management?

 

[Bali]

Thanks Bali. Could a cooler running engine cause unbalanced fuel management?

Yes. Cooler temperature keeps the DME in cold start enrichment mode.
On your next hot idle include the fuel system status for both banks.
Might be a good time to just do all 3 logs, upload to datazap.me, and post links here for review.

 

[nverb]

Thanks, Bali.

I took a log on a cold start this morning and then another log after I drove around for a good while. I did not get a misfire or a SES light on this drive. Also, I am using a MAC computer and it's not compatible with my diagnostic tools to upload the logs to datzap. I'll try and borrow a PC for this in the future.

Here is what I logged on the COLD start at idle:
• Fuel System 1 Status: CL
• Fuel System 2 Status: CL
• Coolant temperature in C: 41°C
• Short term fuel trim bank 1: Fluctuates between 5.5 & 7.8%
• Long term fuel trim bank 1: 0.0 %
• Short term fuel trim bank 2: Fluctuates between 3.1 & 6.3%
• Long term fuel trim bank 2: 0.0%
• MAF value in g/s: 4.34 g/s
• RPM: 687-700

Here is what I logged at HOT idle:
• Fuel System 1 Status: CL
• Fuel System 2 Status: CL
• Coolant temperature in C: 93°C
• Short term fuel trim bank 1: Fluctuates between -2.3 & 0.8%
• Long term fuel trim bank 1: 3.9%
• Short term fuel trim bank 2: Fluctuates between -3.9 & -2.3%
• Long term fuel trim bank 2: 4.7%
• MAF value in g/s: 3.57 g/s
• RPM: 698-705

Does anything here look out of wack?

Also, in regards to the cooling system… I replaced the water pump (ACDelco), water pump pulley (Dorman), thermostat housing/water outlet (Beck/Arnley), expansion tank (Vaico), expansion tank thermostat (Beck/Arnley), coolant temp sensor (Dade), hoses (ACDelco & Gates) and Radiator fan clutch (URO Parts) back in July. These parts are aftermarket (brand in parentheses next to part). Being that these are aftermarket parts, could they be not working correctly and not letting the engine heat to operating temperature at all times?

 

[Bali]

The hot idle numbers look fine. Good to see it at 93 C. Next time you get the misfire fault code include the freeze frame data here so we can see the context in which it misfired. That gives good clues.

Thermostat regulates coolant temperature.
As Markus always says, “Aftermarket cooling system parts are strictly verboten!”

 

[nverb]

Thanks, Bali.

The next misfire fault code I get I'll share the freeze frame data. Stay tuned…

 

[Sapote]

MAF value in g/s: 3.57 g/s
• RPM: 698-705

3.6 is a little high for 325i engine.
Misfire: you might have coolant in #3 engine. Remove spark plugs and compare #3 and others.

 

[nverb]

Thanks, Sapote.

Here are pictures of the spark plugs that I pulled out when I first started having issues. Unfortunately, I didn't label which plug came from what cylinder. The only one that looks different to me is the one on the far right end with the white electrode. These were on the car for about 2.5 years.

Can anyone read these plugs?

 

[Sapote]

The only one that looks different to me is the one on the far right end with the white electrode.

That one looks so odd with the cleaned white ceramic. How often you need to add coolant to the tank?
When did this #3 misfire start happening?

 

[nverb]

Hey Sapote,

I haven't added any coolant since I replaced the cooling system components back in July 2022 (water pump, expansion tank, expansion tank thermostat, coolant temp sensor, hoses and radiator fan clutch). Only things I didn't change was the thermostat housing/water outlet and radiator. Prior to that, I would get the coolant light on the dash usually one time per year and would need to add then.

Here is the full context behind the misfire…

I started having issues with the car back on Dec. 24 2022. It was a super cold day, below zero in Pittsburgh. I turned the car on to warm up and walked away. Came back 15 min later to drive it and the SES light was on and had a misfire. Turned the car off for a few hours, came back and the SES light and misfire went away.

Car ran good until Jan 7th and I got misfire codes on cylinders 2–5 as well as an Activation, ignition, cylinder 5 code. So I put a new coil on cylinder 5 and the car ran good up until Jan 29th.

On Jan 29th, I got a SES light while driving under load. I wasn't home at this time and pulled the coils out while the engine was running to see if any of them were bad and the only coil that didn't cause a change in the engine was #3. So I assumed the coil was bad. Was able to get to a parts store and put a new one on. The car ran good for about 30 miles or so then the SES light came back on with the misfire. When I got home and scanned the car and the codes I got this time were… misfire on 1,3,6. as well as a thermostat map cooling, mechanical jammed open.

So now I decided to replace all the spark plugs, put on a new valve cover gasket because I had some oil on the plugs and coils and put a new thermostat housing/water outlet (this wasn't a cooling part that I replaced in July 2022). Cleared the codes and got a misfire on cylinders 2 & 4. Cleared the codes again after letting the cooling system bleed and got a misfire on cylinder 3 only.

And have been getting the same misfire on cylinder 3 ever since. Usually happens when the car is going up hill (under load) and it happens intermittently. Then it always goes away if I shut the engine off and back on. The car also seems to shut the fuel off to cylinder 3 when this happens.

 

[Sapote]

The car also seems to shut the fuel off to cylinder 3 when this happens.

Are you guessing or the code says so?