Hot Start Problem
02-24-2008, 09:41 PM
#1
Advanced
Thread Starter
Join Date: Dec 2007
Location: Laguna Beach, CA
Posts: 51
Likes: 0
Received 0 Likes
on
0 Posts
Hot Start Problem
This '79 930 engine refuses to start when the least bit warm/hot without falsely triggering the 7th injector. When it does catch and "light" without the false trigger, it shuts down as though it ran out of gas. Any idea what my problem may be?
TIA for your help.
TIA for your help.
02-25-2008, 12:22 AM
#4
Rennlist Lifetime Member
Do you have an accumulator in place and a check valve? the head will evaporate the fuel out in a matter of minutes (About 5-10) and will partially vapor lock making it hard to start. BTW wonderful looking build!
02-25-2008, 12:51 AM
#5
Advanced
Thread Starter
Join Date: Dec 2007
Location: Laguna Beach, CA
Posts: 51
Likes: 0
Received 0 Likes
on
0 Posts
Hot Start Problem
Thanks for your kind comment and help.
Accumulator (plumbed right thanks to your advice) is in the the fuel system, (shows in photo below MSD). Front fuel pump (under fuel tank) has a check valve and is working. Don't know about the pump near the engine.
If engine is warm/hot and shut off for only 15/30 seconds, it won't start. Wait 15 minutes, starts. It's also a start made by opening throttle body just a bit. No throttle or too much throttle and it won't 'catch.'
I suspected vapor lock but engine compartment is force fed with ambient air when ignition is on. No mater how hot the engine gets, fuel head, intake plenum and intake manifold are cold to the touch. They do warm up on soak but the start problem occurs long before anything on top of the engine takes on heat.
Perhaps something in the WUR? Pressures are in spec. Pressure holds within spec for 20-minutes after power shut off. Unfortunately, I know nothing about how the WUR operates.
Chris
02-25-2008, 01:46 AM
#6
Instructor
Join Date: May 2005
Location: Melbourne
Posts: 188
Likes: 0
Received 0 Likes
on
0 Posts
If it's holding pressure after 20 mins then it's not the same problem I had.
Try this web site to get an understanding of how it all works.
http://www.auto-solve.com/mech_inj.htm#MFI10
Try this web site to get an understanding of how it all works.
http://www.auto-solve.com/mech_inj.htm#MFI10
Last edited by goldminer; 02-25-2008 at 01:50 AM. Reason: added link
02-26-2008, 12:50 AM
#7
Three Wheelin'
I saw your beauty at the Ventura Show, very impressive!
Anyway, if you have indeed checked that the fuel pressure holds after shut-down, problem may be elsewhere. If your system/control pressures are indeed in spec, check for air leaks in the intake system (a common cause of CIS no-start unless you hold the throttle down, etc). But I would also check your basic mixture when warm. It is possible for all fuel pressures to be in spec and the WUR working perfectly and still be too lean. If the mixture is too lean, when the engine is hot, might not be enough fuel to start/stay running. Check these out and get back to us!
Anyway, if you have indeed checked that the fuel pressure holds after shut-down, problem may be elsewhere. If your system/control pressures are indeed in spec, check for air leaks in the intake system (a common cause of CIS no-start unless you hold the throttle down, etc). But I would also check your basic mixture when warm. It is possible for all fuel pressures to be in spec and the WUR working perfectly and still be too lean. If the mixture is too lean, when the engine is hot, might not be enough fuel to start/stay running. Check these out and get back to us!
Trending Topics
02-26-2008, 01:11 AM
#8
Advanced
Thread Starter
Join Date: Dec 2007
Location: Laguna Beach, CA
Posts: 51
Likes: 0
Received 0 Likes
on
0 Posts
I saw your beauty at the Ventura Show, very impressive!
Anyway, if you have indeed checked that the fuel pressure holds after shut-down, problem may be elsewhere. If your system/control pressures are indeed in spec, check for air leaks in the intake system (a common cause of CIS no-start unless you hold the throttle down, etc). But I would also check your basic mixture when warm. It is possible for all fuel pressures to be in spec and the WUR working perfectly and still be too lean. If the mixture is too lean, when the engine is hot, might not be enough fuel to start/stay running. Check these out and get back to us!
Anyway, if you have indeed checked that the fuel pressure holds after shut-down, problem may be elsewhere. If your system/control pressures are indeed in spec, check for air leaks in the intake system (a common cause of CIS no-start unless you hold the throttle down, etc). But I would also check your basic mixture when warm. It is possible for all fuel pressures to be in spec and the WUR working perfectly and still be too lean. If the mixture is too lean, when the engine is hot, might not be enough fuel to start/stay running. Check these out and get back to us!
Thanks for your kind comment and suggestions. Will do all suggested, report back.
Stephen/PorschePhD suggested the fuel plate may be too high and I suspect he may be right. I took the assembly apart to polish and reassembled knowing nothing other than what I learned by taking the "air box" or whatever the assembly is called apart. I'm going to check this first, adjust to bias on the side of opening - now biased on the side of being over closed.
Chris
