Engine hesitation when cold below 2000rpm (1 Viewer)

[robnicko]

how is the condition of the air filter?
BTW - where in Aus are you located?

 

[Mfb]

how is the condition of the air filter?
BTW - where in Aus are you located?

Filter is new.

Victoria.

 

[robnicko]

is your air filter housing like the one below and are the vac hoses to the white part in place? Beneath this is a CO2 adjuster as well which affects the Petrol Mixture on AUS delivery models
can you post some pics of the engine bay? this will be very helpful especially as it used to be on LPG
Im in Vic to - Melb

 

[Mfb]

is your air filter housing like the one below and are the vac hoses to the white part in place? Beneath this is a CO2 adjuster as well which affects the Petrol Mixture on AUS delivery models
can you post some pics of the engine bay?
Im in Vic to - Melb


View attachment 3559194

Yep, I’ve got the same setup and all those vacuum hoses are connected as in your photo.

I can post some photos later tonight.

I’m also based in Melbourne.

 

[Mfb]

Here is a photo of the intake system.

 

[Mfb]

Update: I found a leak in the exhaust today between the manifold and O2 sensor. This could be putting the air fuel mixture off.

I’m going to try and tighten the nuts before getting a new gasket.

I’ll report back on whether this fixes my hesitation problem.

 

[Mfb]

Ok, so after trying to tighten the flange nuts and worrying that I was going to break the stud, I took it to the my local exhaust shop. After explaining the story to him, he didn't think that was the cause of the problem but was happy to try and tighten the nuts/replace the gasket.

He suggested I check my theory with a local mechanic on what he thought first before going down that route. After a short drive to the mechanic and also explaining the story to him, he also didn't think that was the problem. I also run this by 'my' mechanic and he didn't think so either.

In the meantime, I have had the ECM checked, and it has passed all checks except for a timing test which they were upfront and said they could test.

Any other thoughts on this problem?

 

[Mfb]

The only way to confirm valve clearances is by removing the valve cover and checking with a feeler gauge. This must be done on a stone cold engine to be 100% accurate.

Popping in the exhaust (at tailpipe) on idle can be an indication of valves not seating correctly and/or a vac leak

When on LPG did you ever get any backfire through the AFM / throttle body as when running on LPG the AFM doesnt really do anything but when running on petrol it does and you did mention that on LPG it ran fine?

Furthermore, I can also confirm there is a popping sound from the exhaust at idle when at normal operating temperature.

I have confirmed again with my mechanic that he completed a wet and dry compression test and compression is ok.

 

[OfficialGamings]

I would also have to agree with your exhaust guy and Mechanic. O2 Sensors run in open loop when the engine is getting to operating temperature which means the ECU doesnt use that data until it reaches closed loop. So In that case your exhaust leak would be worse when the engine is warm. Just my thought.
But in saying that I also recently replaced my O2 Sensors but with Bosch sensors instead but I no longer have check engine light for it. So I assumed it was all good

You could try looking at the coolant temp sensor for the ECU, I believe this rigs have 2. One for the gauge on the cluster and one that sends data to the ECU.
I personally havent checked mine yet but thats on my to do list.

I had a very small exhaust leak before O2 Sensors. But even after patching still having the same issues.

 

[Mfb]

I would also have to agree with your exhaust guy and Mechanic. O2 Sensors run in open loop when the engine is getting to operating temperature which means the ECU doesnt use that data until it reaches closed loop. So In that case your exhaust leak would be worse when the engine is warm. Just my thought.
But in saying that I also recently replaced my O2 Sensors but with Bosch sensors instead but I no longer have check engine light for it. So I assumed it was all good

You could try looking at the coolant temp sensor for the ECU, I believe this rigs have 2. One for the gauge on the cluster and one that sends data to the ECU.
I personally havent checked mine yet but thats on my to do list.

I had a very small exhaust leak before O2 Sensors. But even after patching still having the same issues.

Thanks for your reply.

I agree, I have also recently replaced the O2 sensor with a NGK sensor, but that didn’t solve the problem. I don’t have any check engine lights either.

I have already replaced the coolant temp sensor to the ECM recently, it did not fix the problem…?

 

[OfficialGamings]

Hmm I see, I missed that post.
The only other thing I could think of at the moment would be fuel pressure regulator but I would think it would be a constant issue and not just when engine is warming up.

But going back to what TrollHole had said about the temp sensor in the AFM. This could still be a issue. ill try find it in the TCM for yah.

THA-E2 Should be the Temp Sensor in the AFM. TCM Diagram PDF for yah too.

 

[Mfb]

Hmm I see, I missed that post.
The only other thing I could think of at the moment would be fuel pressure regulator but I would think it would be a constant issue and not just when engine is warming up.

But going back to what TrollHole had said about the temp sensor in the AFM. This could still be a issue. ill try find it in the TCM for yah.

THA-E2 Should be the Temp Sensor in the AFM. TCM Diagram PDF for yah too.

The fuel pressure regulator, fuel filter, pump and relay have been replaced.

I’ve tested the AFM and it meets the FSM. I’ve also had it flow tested and it passed with flying colours. There is a lean/rich mixture screw that I haven’t tried yet which might be worth playing with. I understand left is lean and right is rich.

 

[CharlieS]

In the meantime, I have had the ECM checked, and it has passed all checks except for a timing test which they were upfront and said they could test.

Testing timing is easy with a timing light and a jumper wire. Find a mechanic old enough to own a timing light, and bring them the page from the manual with the procedure. Or better yet, buy a timing light and a paper clip and be able to check/adjust your timing now and forever more.

 

[Mfb]

Testing timing is easy with a timing light and a jumper wire. Find a mechanic old enough to own a timing light, and bring them the page from the manual with the procedure. Or better yet, buy a timing light and a paper clip and be able to check/adjust your timing now and forever more.

Thanks for your input.

I was referring to the timing parameters of the ECM, apparently it can’t be tested on the bench.

Timing is at the standard 3 degrees.

 

[Mfb]

Would someone be able to post pictures of their FZJ80 engine bay?

I’d like to check and compare all vacuum hoses to ensure mine is plumed up correctly.

If you could post shots from the left, front and right side, top down if possible.

Thanks in advance.

 

[Mfb]

Could someone also please share a clean photo of the vacuum hoses under the manifold?

I‘d like to check that hoses are connected correctly.

Thanks again.

 

[Mfb]

I removed and cleaned the IAC, there was a fair amount of carbon build up on the plunger and in the port. I cleaned it and refitted the IAC but that didn’t fix the issue.

Something else I’ve noticed is when the car is first driven, when the engine is cold, it runs great, it starts to hesitate within ~30 sec of driving, and then runs great agin once at full operating temp.

I also notice that the hesitation is worst at take off and below 1200rpm and comes good at about or just below 2000rpm as I drive through it. Furthermore, if I push the pedal to wide open throttle (to the floor) it seems to come good, other times I’ve heard a pop or small backfire from what seems to be at the from of the exhaust (maybe at the exhaust flange as pictured previously), not sure.

Best to be sure, I tested the coil resistance today, primary and secondary values are in spec.

Please keep the suggestions coming through.

 

[Mfb]

I've managed to get some live data during the initial warm up, but I would appreciate some help to interpret the data

 

[Mfb]

+

 

[Mfb]

+