Trouble starting when warm

arknotts

arknotts

formerly ark86
Jan 9, 2008
461
1
18
Ohio
First off, my setup is nowhere near stock running on a stock ECU with a Maft Pro. I realize this won't be perfect and isn't optimal, but I know something isn't right. Relevant mods are:

* Aeromotive A1000 fuel pump and respective Aeromotive regulator (-10 feed/-8 return)
* 680cc injectors
* Maft Pro running speed density
* IS300 coils
* BC 264 cams (Intake: -2, Exhaust: +3)
* Base timing is set to -10 degrees BTDC like stock for now
* I AM running the stock ISCV, and it clicks after shutdown

The car starts up great when cold. The problem occurs when I shut it down warm and try to start it back up. It could sit for 15 minutes and still not start up, or even if I stall it and try to start it back up immediately it won't. The engine catches immediately, revs to about 1,000 rpm and then dies immediately. Consistent results every time. If I pull the EFI fuse, and crank for about 5-10 seconds, put it back in and start it up with 1/4 to 1/2 throttle it will rev to 1,000 rpm, act like it wants to die but then barely catch itself and then it's fine. Only code is a TPS code from the Maft Pro (I've always had this, even before the rebuild...it didn't affect it then).

As a disclaimer, other than the ISCV I have none of the stock amenities such as EGR or the VSVs. I know not having these isn't the best for the stock ECU, but I also know it won't cause the issue I'm having. Any input would be appreciated. It's really annoying, as I don't like driving it until I can get this resolved (if the engine stalls, I can't get it restarted easily!)
 
J

jonahs_supra

Active Member
May 17, 2011
1,015
0
36
Lancaster, Ohio, United States
Hmm I don't have a tps code. I'm running maft pro in speed density. No problems at all
Well I did find after installing my aeromotive afpr. Letting the car sit for a few hrs the fuel pressure would bleed off
So when I go to start it'll catch on 1 cylinder then die. Another turn of the key then its fine and runs perfect
 
arknotts

arknotts

formerly ark86
Jan 9, 2008
461
1
18
Ohio
Funny thing is it worked great before the rebuild. Tune and everything is the same, just new turbo and fuel system. I've manually jumpered the fuel pump to build pressure and tried to start it...same issue.
 
jetjock

jetjock

creepy-ass cracka
Jul 11, 2005
9,439
0
0
Redacted per Title 18 USC Section 798
Assuming timing, spark, and cranking vacuum are OK hard starts are almost always mixture related. Do you know what it is? If not try making it both ways to see which causes improvement then go from there. And fix the TPS code. It's not from the Maft.
 
arknotts

arknotts

formerly ark86
Jan 9, 2008
461
1
18
Ohio
jetjock;1869364 said:
Assuming timing, spark, and cranking vacuum are OK hard starts are almost always mixture related. Do you know what it is? If not try making it both ways to see which causes improvement then go from there. And fix the TPS code. It's not from the Maft.
Click to expand...

Thanks for the insight JJ.

Timing is OK...timed at -10 at proper idle warmed up.
I'm assuming (knock on wood) spark is OK since it runs fine otherwise (not ruling it out though).
My vacuum is a little low (15-16 in/hg at warm idle), but I know it's at least partly due to my cams. I really don't know what it should be with these.

I was thinking it's mixture related too, as it spits out a little smoke right before it dies (extremely rich?). I still don't know why it fires immediately and then immediately dies though. Trouble is, I don't know where to start if it is mixture related. Only thing I can think of is the ECU water temp sender isn't right. The wiring checked out OK, I'm going to test the resistance today to make sure it's reading properly.

The TPS code (41) is from the Maft in my case. I have enhanced TPS wired up, in which the Maft unit supplies a modified TPS signal to the ECU. Since the TCCS starts up before the Maft it doesn't see a TPS signal and throws the code. I have it wired up to the ACC power, but sometimes still forget to pause there for a second. Even when I reset the codes it still does it.
 
jetjock

jetjock

creepy-ass cracka
Jul 11, 2005
9,439
0
0
Redacted per Title 18 USC Section 798
Ok, my bad on the Maft/TPS thing. Wasn't aware they could do that. I only know about the AFM code. Is the Maft supplying a TPS signal during cranking? That would not be good.

Is fuel rest pressure holding? Fwiw unplugging the coolant sensor equals a hot engine so if it starts OK cold it's unlikely to be the problem. If you were having cold start issues that'd be different. Try making the engine rich and lean while cranking to see which helps. You don't have a WB?
 
3p141592654

3p141592654

90T
Oct 11, 2005
3,816
16
38
Thousand Oaks, CA
My suspicion is the synthesized AFM KS signal from the MAFT Pro is glitchy. Do you have an oscilloscope that you could monitor KS during startup and then stall?
 
arknotts

arknotts

formerly ark86
Jan 9, 2008
461
1
18
Ohio
3p141592654;1870383 said:
My suspicion is the synthesized AFM KS signal from the MAFT Pro is glitchy. Do you have an oscilloscope that you could monitor KS during startup and then stall?
Click to expand...

I do have a small one. I'll see if I can get it hooked up.

JJ, I still need to look into your suggestions, just haven't had time.

Thanks guys, this is an odd one.
 
planemos

planemos

New Member
Apr 22, 2011
559
0
0
Slocan Park, BC, Canada
I'm just throwing it out there but it could be oil in the mix. Either bad valve seals or bad turbo (I don't know the details on how long you've been running your turbo, what it is, who rebuilt it etc). I was having smoking and hard starting with hot engine problem and my turbo has definetly got too much play in it, now that I checked my car out. Are your plugs getting wet?
 
arknotts

arknotts

formerly ark86
Jan 9, 2008
461
1
18
Ohio
OK, I'm sure I found the issue. This should have been more obvious to me! While cranking, the Maft Pro loses power. When cold it revs high enough so it's able to boot in that split second and recover. When warm it dies before it's able to boot again. 3p, thanks for the suggestion that is exactly what is happening and is what led me to this :). I'm going to pull out the TEWD and try to track it down, but if anyone knows what would cause a loss of power to the +B terminal of the ECU while cranking it may save me some time.
 
arknotts

arknotts

formerly ark86
Jan 9, 2008
461
1
18
Ohio
Alright, it's been a while since I installed my Maft Pro. I had forgotten I didn't even have the power connected to +B anymore (to help with the TPS code). I'm switching it back for now and it seems to have worked. I'll test it for real with the engine warmed up but I'm confident this was it. Thanks for the help guys.
 
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