LS1 Transplant won't start
 

I guess I misposted this on another thread but here it is.....

I'm pretty new to the site and spend most of my time at another fourm but
ran across this one awhile back and thought another visit might help resolve a problem.
I have transplanted an LS1 and a 4L65E into a 56 Olds, Rocket 88.
http://dogtagsvette.5u.com
Problem is that although the car runs and handles fantastic, it has an intermittent starting problem.

Here's what I've done and what I know.

When cold, the car starts every time.
When warmed up and operated, the car runs perfect.
When stopped and restarted within a few minutes, perfect!
When stopped for 5 or so minutes, the car will NOT start.
When let sit for 20 minutes, the car will then start every time.

I can duplicate the condition at will.

I've made the following measurements and done the following......

New and reprogrammed ECM. No change
Checked that fuel pump is getting voltage. I can hear it run and it has voltage during cranking. Voltage is the same
run or no run.
Put a scope on injectors. They get 12 volts on the hot wire and
a pulse on signal wire run or no run.
Put scope on spark plug wire and get pulse run or no run.
Anti theft system disabled.

I have not...

Checked crank or cam position sensors...not sure what to look for.
Checked fuel pressure in run or no run states.
Checked fuel filter. (New tank, new pump, new filter 3K miles ago)


Any thoughts, guys?
I know this is like trying to gey your doctor to examin you by phone but any
thoughts are welcome.

By the way, this is my first post so it might take me awhile to figure things out.

Dogtag

I'd carry a $5 Pep Boys noid light injector tester w/ me, and pop it on during the problematic starting to see if the injectors are being pulsed.

Checking fuel pressure during no-start is also a good idea on your list.

If you have a scantool, check the RPM reading while cranking during no-start...that will point you at problematic crank or cam sensors.

Are you running an intank or inline fuel pump?

Have you tried hitting the fuel tank when it wont start, to slosh a bit of fuel around?

Do you have all the smog gear hooked up?

When you say it wont start, do you mean like you have to wait 20 minutes or so to cool before it will start again? Or it just cranks over for a while before firing?

sorry to say i dont have suggestions, though i will probably have problems when i actually start my swap. just wanted to say that is one of the best looking 88s i have seen, cant wait to see it with the green

how hot does the fuel rail get when its having this problem?

if you can safely tap the fuel pressure check valve, does it spray fluid or vapor when its "non-starting hot"??


ive never heard of a LS1 having vaporlock, but if its cranking (from your post i assume not starting is cranking, but not firing) and the injectors are pulsing, and the fuel pressure is there, and the spark is there..........thats my only idea.

if you havent done so, check the fuel pressure before the problem and then when it wont start....

How close is the exhaust system to the starter? Could it be something as simple as "the hot starts"? The starter may be soaking up too much heat and affecting the selanoid.

Um...it appears to crank fine, just won't actually start...

Do yourself a favor and replace the starter relay. I've seen a bunch of occasions where this is the case.. eventually it won't start anymore.

It seems as if the possibilities are endless here but I'll lend my experience to the mix to see if it can help. I had the exact same scenario: Cold start is fine and would run for 1000 miles if you never shut off without a miss or a hiccup but after the engine was hot and you shut it off it would spin over without firing - I found this out at a fuel stop. After twenty to thirty minutes it started right up and I was on my way. After this initial incident it would reoccur like clockwork. This car was a driver so I did not have time to tinker with it myself. I took it to the dealer and 3 hours later they called and said it needed a crank sensor. They replaced it and the problem was eliminated. This was last summer and the symptoms have never reoccurred. Hope this helps but can't guarantee.

Clay

LS1 Transplant won't start
 

Thanks, Clay.
You described my symptoms to a tee....
Thats exactly whats happening.
It's strange that the car will start after 20 or 30 minutes but that's exactly what it does.
I ordered a new sensor. The're only 50 bucks.

Dogtag

intresting.. if this solves your problem, please post up.. ive never heard of that happening...i wonder why the wait "fixes" it.....

If you do the crank sensor and still have a problem, put a pressure gauge on the rail and watch the pressure when you shut it down. If you have a questionable injector that sits there and dribbles fuel for 20 minutes, it may not want to start real well or not at all.

Special thanks to Clay.
Replacing the sensor seemed to solve the problem. What a pain in the ass that
was.
I'll bet your ride had you pulling your hair out.....
Anyway, time to put some miles on the thing now.

Thanks again
Dogtag

i seen that problem happening on various cars ...some where low fuel pressure when warm others....bad check valve at fuel pump when warm...also leaky fuel injectors when warm

Good to see it running, I have seen things like that often. Most know some parts just heat up faster and hotter after the engine shuts down. The test I always did was, when it acted up in your case get some cold water in the area to see if the pattern could be changed. If so the part cooled off by the water is likely the skewed one. Surely you have to have control of the test conditions.
The "odd" part of your situation is a skewed crank sensor wont signal the ECM to pulse the injectors so somewhere that was missed in the diagnosis of the list of sub-systems.
Good team work by the forum! :hail:

my first thought was waporlock as well, may be getting to hot and boiling ur fuel. but glad to hear it was a simpler problem.