NA with a VVT swap Question
 

Hey guys, I am 3rd weekend into troubleshooting and I feel like I am getting no where.

I'll start with the issue I am having and follow up with things I have tested and tried before coming here.

ISSUE:
Cranking the car to start tries to start off what sounds like one cylinder but after cranking 5-10 seconds it backfires. It's not completely consistent when backfiring but it happens often enough.

THINGS I HAVE:
1) Stock VVT Batchfire CoPs
2) Injector Dynamics 650cc injectors
3) Stock VVT Bottom end and stock VVT head.
4) MS3PNP Pro

THINGS I HAVE TRIED:
1) Pulled intake mani and tested/confirmed firing and correct order of all injectors. "Cylinder1:InjectorA", "Cylinder2:InjectorD", "Cylinder3:InjectorB", "Cylinder4:InjectorC" (Cylinder 1 is front most cylinder and they count backwards.)
2) I am running stock VVT batch fire CoPs. I tested they were firing on the expect coil "CoilA:Cylinder1/4", "CoilB:Cylinder2/3"
3) Pulled an assortment of sensors like the cam and crank sensors to make sure they weren't causing issues.
4) Downloaded a base tune for Megasquirt MSPNP
5) Setup the MS3 for Sequentual injection (1,3,4,2 firing order)
6) Setup MS3 Engine Displacement for 1839ccs
7) Setup MS3 for Batch spark
8) used canBUS debugging to test all injectors, spark plugs and pump.

THINGS TO NOTE:
I have the tachout resisted to 1000k ohms
I have mostly followed Car Passion Channels guide as well as a lot of info in the VVT megathread.

I don't think I am missing anything but man I have put so many hours into this and I am stuck. I feel like it's down to a config issue in MS3 but I took a stock tune and only changed what I thought would be needed.

It sounds like a timing issue. Either trigger settings in TS or mechanical.

but without a tune and a log attached, we can’t really help you.

I was thinking time as well but I was afraid to be wrong and tear through the VVT solenoid and valve cover to be wrong. I will get a tune dumped tomorrow since it is almost 10:30PM here right now and I am drained. I might just decide to tear into it tomorrow to verify anyway. I don't have any base timing set in MS yet since it hasn't actually even started.

Youve confirmed the firing order of the injectors and coils correctly but order is not enough, You need to confirm timing with respect to crank angle

Get a timing light on the crank pulley

Okay sorry guys, I was helping a friend move yesterday and was wayyyy to tired to get back into my garage.

I have my entire data logs and tune in this share.
https://drive.google.com/drive/folde...Y0?usp=sharing

All the testing was done without coils plugged in because I didn't want to keep backfiring. My neighbors still like me.

I couldn't get a timing light on it since I was doing this by myself.

I kind of looked it all over but this is my first swap and I am most likely missing something obvious or important.

Please lend me your great knowledge.

Did you install a new timing belt before you swapped in the motor? Have you verified that physical timing on the motor is good, and that the timing belt has not jumped a tooth or not.

On mobile so i cant open the tune but i had very similar issues.
try "falling edge" spark and 01-05 miata trigger settings.

So a little background to justify my stupidity. I bought this engine from a trusted source about 5 weeks ago. The car was in a minor front end collision previously. It was enough to throw the air bags. He has since fixed the damage to the car, put his own built VVT into the car and turned it into a SPEC Miata. The car was running before the collision just fine and it in no way should damaged the engine.

All this being said, I will try the falling spark thing to give it one more try and then pull the valve cover tonight to verify mechanical timing.

I will update this thread about 12-13 hours from now with that information.

Thanks a ton everyone, I do realllly appreciate it! :noob:

I had what sounds like a very similar issue when I first started my vvt swap. This completely fixed the issue.

You're giving me hope yet! I can't wait to get off of work!

Falling edge triggering for 99-05 Miata did not work. I am not getting backfires anymore though so I don't know why that is. I even set it back to rising edge and no longer get backfires.

I do however have a new idea, totally forgot to get my 90-93 coolant temp sensor. I don't know if that could cause weird changes in firing time but I don't see why it couldn't. I will run and grab one tonight to see if it helps. If not I will take the valve cover off I guess!

Alright, I pulled it because I realized the oil feed was easier to move than I thought.


https://cimg7.ibsrv.net/gimg/www.mia...58c36b0ec1.png
Engine definitely looked in time. I have never timed a VVT but from what I looked up it looks good.
https://cimg0.ibsrv.net/gimg/www.mia...ee2deb0115.png
I don't know where the CAM sensor should be when the trigger is passing the sensor but this is the current state.
https://cimg1.ibsrv.net/gimg/www.mia...04cb0a600d.png
https://cimg2.ibsrv.net/gimg/www.mia...ce84c88354.png
Also just wanted to take a minute to appreciate how clean this engine is. I hadn't opened it up at all yet.
https://cimg3.ibsrv.net/gimg/www.mia...464e8819f2.png

That cambelt looks like its about to fall off from how loose it is
Your cam timing is probably out

+1
Im no expert but from my experience the timing belt should be straight from one cam to the other. Yours looks bowed out from not being tight enough. But then again, my limited experience is on non VVT motors.

So yall made me paranoid and question myself even though I have pictures of it in time. I pulled the valve cover back off as well as the from timing cover. Everything checks out and is perfectly in time. The slack on the top is because depending on the angle of the cams, it might see more or less tension.

One other thing. I feel like I am on to something. I have checked every sensor and output on the car. Everything works... Except for Tach out specifically to the Megasquirt. It works on the Dash but doesn't show any changes when tshooting the canbus tachout pin specifically on the MS3. I feel like this is it but I need to read a little more to understand how exactly it should reach my MS3.

https://cimg7.ibsrv.net/gimg/www.mia...c2e9097e33.png
https://cimg8.ibsrv.net/gimg/www.mia...2c907c6c0c.png

There is a tension mark on the oil pump, as well as the timing cover. Rotate from TDC 1 and 5/6th turns, which should line up with the tension mark. Release the tensioner bolt and retighten. I sometimes see the most slack a tooth or so before this mark, so I tension there. Then rotate the remaining 1/6 turn, and 2 additional, and verify you’re still in time.

I will try to do this tomorrow at lunch. I'll come back with results.

The tachout to the actual MS3 isn't a concern? I get a signal to the dash but not the MS3. I am reconfirming how I should wire that right now too.

If the ms3 isn’t displaying RPM, it’s an issue with cam/crank sensors, and it’ll never run. It then uses this data to send a signal to the tach, however you’re reporting otherwise, so not sure I’m under standing you correctly.

Yeah so to clarify, When testing with CanBUS tshooting. My tachout pulsed at 78hz will bring my dash tach to about 2500rpm but my MS3 will never detect anything. A new thought I just had to was maybe I don't need tachout jumped on my MS3 since I am running stock 01+ cops and not LS coils right now.

To be transparent, I bought a cheap set of Crank and Cam sensors off of Ebay but based on the logs. I don't think those are the issue anyway but I am open to being wrong at this point. lol