Hard cold-start problem. Helps? - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


Engine Performance This section is for discussion on all engine building related questions.
Sponsored by:
Sponsored by:

Reply
 
 
 
LinkBack Thread Tools Search this Thread
Old 12-03-2010, 12:59 PM   #1
Elite Member
Thread Starter
iTrader: (12)
 
Join Date: Sep 2007
Location: Charlotte, NC
Posts: 6,868
Total Cats: 66
Default Hard cold-start problem. Helps?

So ever since I replaced my engine back in July, I've been having an issue on cold-starting. It's only on VERY cold starts like overnight and after the car has been sitting while I'm at work. I have Hydra 2.17 and I know it cranks the engine more than normal to check timing before giving fuel/spark. But this issue is much different.

On the first attempt to cold start, the engine turns over normally and then starts to fire, but it just sputters badly and stalls out. *Sometimes* it will sputter and idle at like 200rpm and then cut off. Upon the next attempt to crank everything will work normally. I've tried feathering the gas while turning it over to see if it changes. It seems to make some difference and will sometimes sputter -> low shaky idle for a couple seconds -> "find" itself and idle normally.

BUT

Lately with the temperature being much colder, it's taking 2-4 attempts to fire up. Once it runs, I can turn it off and it'll crank right back up normally.
I don't think it's fuel enrichment/cold start settings or excessive fuel. I don't get any excessive fuel smell from the exhaust (like I do when it sometimes stalls and takes a moment to crank up..but that's another issue for another day).

The only thing I can think of is that the crank sensor is just a fart too far away from the crank pulley and signal isn't great when cold starting...like the metal has contracted enough to cause a weak signal pickup. When we swapped the crank sensor over, we used a feeler gauge that the FSM calls for...but it may have moved when tightening down. Anyone ever had a similar issue?
Doppelgänger is offline   Reply With Quote
Old 12-03-2010, 01:08 PM   #2
Tour de Franzia
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

change the fuel enrichment, bitch.
hustler is offline   Reply With Quote
Old 12-03-2010, 01:21 PM   #3
Elite Member
Thread Starter
iTrader: (12)
 
Join Date: Sep 2007
Location: Charlotte, NC
Posts: 6,868
Total Cats: 66
Default

Would the enrichment really be different between starts that are 2 seconds apart Sir Homobottomofthebarstool Sr.?
Doppelgänger is offline   Reply With Quote
Old 12-03-2010, 01:28 PM   #4
Tour de Franzia
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

Quote:
Originally Posted by Doppelgänger View Post
Would the enrichment really be different between starts that are 2 seconds apart Sir Homobottomofthebarstool Sr.?
I imagine that a couple rounds of flame through the clyinders warms-up things dramatically. I recently fixed this in my car where adding .2ms cranking fuel in one cell made it go from 3-5 cranking attempts to the first time, every time. My after start enrichment still needs a touch more work, but now the car starts the first time rather than a few crank attempts.
hustler is offline   Reply With Quote
Old 12-03-2010, 02:12 PM   #5
Elite Member
Thread Starter
iTrader: (12)
 
Join Date: Sep 2007
Location: Charlotte, NC
Posts: 6,868
Total Cats: 66
Default

I shall look into it then. I really question because the entire life of the previous engine, there was no starting issues at all and it only started when I replaced the engine. I know the fresh engine has a bit more compression due to it's newness...but enough to make a significant difference in starting? The previous engine was boosted very early in it's life...so I wouldn't imagine that the cold-start enrichment would be much different on a fresh engine. At least that's my idea behind it.
Doppelgänger is offline   Reply With Quote
Old 12-03-2010, 02:20 PM   #6
Senior Member
iTrader: (4)
 
Join Date: Jan 2008
Location: Falls Church, VA
Posts: 1,367
Total Cats: 16
Default

Adding cranking pulse width would be the first thing to try. You really only get one crack at that per day, on the very first cold crank in the morning, because once you burn fuel, even if it's just enough to make it stumble, that heat will affect the next crank attempt as hustler has pointed out.

Does the Hydra have a field where you specify cranking rpms? In other words, the rpm below which it will still inject cranking pulse widths before switching over to the running fuel table? In my MS I adjusted cranking rpm up to 400 (was originally 250 or 300 IIRC) and it seemed to help keep it from doing the 250 rpm stumbling and dying routine. If you get to the point where it seems to crank and catch "pretty well" (as opposed to just stumbling) and then dies right away, you need to bump up the after-start enrichment % at that temperature. This is MS terminology as I'm not familiar with Hydra but the concepts should work more or less the same.
ScottFW is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
1991 special edition with hard top full part out JC, NJ russian Miata parts for sale/trade 6 10-08-2015 04:01 PM
Expected intake temps on the track? tazswing Race Prep 20 10-03-2015 12:04 PM
WTB HPDE miata - Texas Voltwings Cars for sale/trade 0 09-27-2015 07:40 PM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 01:53 AM.