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Not running after head gasket

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So I've just replaced my head gasket on my SR S15 with a link g4+. car was running perfectly fine before I pulled it apart and now it barely runs.

could not get it started at all on tuned map tried everything tried 3 different cas's. So I tried the base map with base timing from tune and it eventually started but barely ran at all running very very rich. have checked over everything timing wiring etc so many times everything seems fine. Had a stock head gasket so 1.1mm and now has a tomei 1.2mm head was machined not sure how much was taken off but it barely needed machining so imagine not much at all. I couldn't imagine the slightest change in compression would cause it to not run like this. compression test 130psi exactly on all 4, dry and cold test yes pretty low but nothings changed since running perfectly fine before.

So basically wondering if there's anything I can try to get it running fine. Going to get it checked out and re tuned anyway but curious as to what it could be and would love it to be running properly.

Open to any suggestions thanks.

Pull a log of your AFRs to see if it is running too rich or too lean @ idle. Also confirm that you are getting proper spark/fuel/airflow.

Also check for fault codes on the ECU,

have you compression tested it since doing the head?

Is the timing chain definitely done right and CAS installed right?

If you could datalog you starting it and I'll happily take a look.

that compression test was after installed. Yes spark on all 4 and fuel. sweet ill do a datalog when I get a chance. yes i've tried pulling out cas and re installing over 30 times definitely installed right. checked with a timing light and everything seemed spot on.

If everything was ok before you changed the head gasket, then the most likely scenario is that either the cam timing is incorrect or the CAs is timed incorrectly.

Cam timing in particular on an SR20 is a little tricky to setup. I would recheck this before going too much further. I've attached an image that shows how the cam sprockets should look at TDC on number one cylinder.

Yea already followed that picture re checked it over and over and everything is fine, counted each tooth individually. Had the cams out quite a few times and re checked. Marks are at correct position on sprockets and perfect amount of links in between. It's got me stumped. Unless chain feel off the crank in the process which is very unlikely because I had tension on it the whole time. But that would mean position of cams would be out when at TDC. Having previously an STM trigger disc and putting the normal disc in effect anything? it wouldn't start with the STM disc anyway. I had a problem once before where I pulled the cams out put in Cas correctly it wouldn't start, so I pulled it out rotated it 360 degrees and it started straight away.

If you swapped the trigger disc then you need to go through and change the trigger mode from multi tooth to Nissan 360 opto. If this hasn't been done the ECU won't know what is going on when you are trying to start it.

Ok thanks heaps Andre i'll give that a go, hopefully it finally solves my issue.

When you change the trigger mode you will also need to recalibrate the base ignition timing.

Another trap is that often the ignition timing can seem like it's correct but the engine won't start. In this case you may be timed up on the wrong engine cycle and the spark is firing during the exhaust stroke. You can change the calibration angle by 360 degrees and this will move you to the correct engine cycle.

Did you get it started?... was it the valve timing?

Nope changed the trigger setup done base timing. Checked timing once again everything seems correct. Still doing the same thing starts on base map but runs real bad like it's on 3 cylinders and super rich

If you click on the 'triggers' tab in the run time values window, is it showing any trigger errors when cranking or running?

Have you actually made sure that the CRANK timing is in sync with the cam timing. You said that you weren't really sure whether or not the chain had slipped a tooth on the crank sprocket when you reinstalled everything. If i was at this point i would just get a telescopic dial indicator and measure the valve timing outright!.

Hey Andre, just got the car back together and yes it has a trigger error. Trig Err Counter 1. what does that mean exactly?

This means that the ECU isn't seeing what it expects to receive from the trigger inputs. It could mean it's seeing either more or less teeth than it expects relative to the sync input or alternatively it may not be getting a sync input at all.

I'd suggest checking on that same screen during cranking to make sure both Trig 1 and Trig 2 are turning green and saying 'OK'. This will show you that the ECU is receiving inputs from both sensors. If this is correct and you're still cycling errors then i'd be looking carefully at the trigger setup and make sure it's correct.

Just a note here - It's not uncommon to see one or two trigger errors when you initially start cranking the engine but if the trigger counter continues to climb then you have an issue.