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Engine wont start/run after it is warmed up

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#1
Tao

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Hi guys,

I'm turning a '92 spec miata into an endurance car only......Increased compression, more work on the head than spec miata allows but nothing crazy......this will be normally aspirated only--no forced induction.

 

Installed engine, started up and ran great, at least around the block.....didnt have a problem then but also might not have  warmed it up fully either.

next step was to change the ECU.....I installed a Hydra Nemesis unit from flying miata which included an A/F sensor (in place of the stock O2 sensor),   a AFM removal and replace with a

Air Temp sensor   and   hooking up different wires to the number 3  and  4 injectors to run sequencialy instead of batch firing...

Their ECU came loaded with the "best" mapping for my application already installed from flying miata.....it looked like all of the basic perameters were good when first hook up to the computer.

 

engine starts fine, runs fine. throttles up fine    but    after it is up to operating temperature it cuts off and wont restart.

 

I will be checking all of the grounds and fuel delivery later today.......

 

just wondering if any one has run into this problem before?

 

since the stock O2 sensor is not connected---would that cause a problem?

 

the guys at flying miata say it is an engine problem not thier ecu........your thoughts?.........eventualy if I cant find the source of the problem I will change back to stock engine management to see if that makes a difference and know for sure.


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#2
MPR22

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Hi guys,

I'm turning a '92 spec miata into an endurance car only......Increased compression, more work on the head than spec miata allows but nothing crazy......this will be normally aspirated only--no forced induction.

 

Installed engine, started up and ran great, at least around the block.....didnt have a problem then but also might not have  warmed it up fully either.

next step was to change the ECU.....I installed a Hydra Nemesis unit from flying miata which included an A/F sensor (in place of the stock O2 sensor),   a AFM removal and replace with a

Air Temp sensor   and   hooking up different wires to the number 3  and  4 injectors to run sequencialy instead of batch firing...

Their ECU came loaded with the "best" mapping for my application already installed from flying miata.....it looked like all of the basic perameters were good when first hook up to the computer.

 

engine starts fine, runs fine. throttles up fine    but    after it is up to operating temperature it cuts off and wont restart.

 

I will be checking all of the grounds and fuel delivery later today.......

 

just wondering if any one has run into this problem before?

 

since the stock O2 sensor is not connected---would that cause a problem?

 

the guys at flying miata say it is an engine problem not thier ecu........your thoughts?.........eventualy if I cant find the source of the problem I will change back to stock engine management to see if that makes a difference and know for sure.

Mmmmmm.  Me thinks they have a bad ecu.  Why in the world would it run fine until it hits operating temperature then turn off.  All of the things that could cause that are related to the ecu.  You aren't loosing fuel pressure, when it gets hot, you aren't loosing spark at least not at idle when it gets hot.  They took out the AFM so that is the usual suspect so its not the cause.  How could they say its not the ECU?   


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#3
Tao

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That is exactly what I was thinking......but by saying its the engine and not the ECU they can try to avoid a return and refund situation........

I just want to get this thing running and thought I would run this by you guys to get your input/opinion..........thanks for your response BTW.

 

has anyone had dealings with Flying Miata?     this was my first time buying parts from them.


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#4
chris haldeman

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Look at every temperature related map on the ecu.no aftermarket ecu I have worked with has had enough fuel enrichment for hot starting. Now why it stalls I am not sure but likely it is either stuck in cold start map or switching to a very poorly programmed hot map. I am willing to bet it is very simple.
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#5
Tao

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Thanks Chris.


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#6
Dave D.

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Does it restart when cooled down? Time to do some old fashioned diagnostics and don't guess. If it cut off and will not start, what is the engine lacking? Fuel, spark, compression, injector pulse, valve timing? Blown fuse when a fan came on? Even if you don't find what the problem is right away, making a list of things that are not the issue will help narrow down to the solution.



#7
Erik Hardy

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An ignition coil that is is going out, parallels your symptoms.


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#8
Tao

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thanks Dave......thanks Erik.

 

Yes the engine restarts when cold........... thanks for the heads up about the coil....good thing I always carry a spare coil pack.

 

Interestingly enough, the car started, warmed up and ran for a good long test drive......this was after checking things but not changing anything......I'm thinking Erik's coil pack going out theory is in play here........???


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#9
Steve Scheifler

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Well, it's very unlikely to be the "engine" but could be anything on the engine that supplies a signal to the ECU. Their ECU may be more dependent/sensitive to a particular input than the stock one. I was going to tune one of those for the first time recently but the engine had more seious issues so I am not yet familiar with their software. It is highly regarded by some so I would expect it to have logs that can be turned on and monitor all required sensors, which may provide a clue. (Megasquirt offers a lot of that despite being a "lower end" product).

Otherwise as others have said, it comes down to the basics, first confirming fuel, spark and timing when failing to start (we know it has compression).

Sorry to hear that FM was not more help, I generally hear good things about their support in general and their engine management in particular.
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