Hello,
I just finished installing a Crate LS7 connect and cruise 4L75E transmission in my 69 convertible.

It cold starts every time and runs great when already running.However after I stop the engine she refuses to start until she sits for about 1/2 hour. Then she starts perfectly again.
For example, jump in car, run to gas station a few miles away, shut her down, fuel her up, and sit for 30 minutes to get her to start.

I have 57.9 lbs of fuel pressure, air intake temp is 120 degrees, coolant temp is 198 degrees, and she cranks over very strong and fast. Just no fire.
I've cleaned the MAF and have a fresh battery with enough cold cranking amps for C6 Z06.

I'm looking for ideas to look at next.
My only thought is to crawl under her and look for cooked wires like O2 sensor, crank position, etc.

Help anyone?
Scott

 

That's usually a crank sensor issue.

Seen fuel pumps do it a few times too.

Hook up a fuel pressure gauge and run it and shut it off. See if it builds fuel pressure right away when you hit the key. Also see if the fuel pressure drops rapidly when you shut it off or if it holds and lingers.

Have a test light handy. Run it and shut it down, hook your clip side of the test light to the battery ground or a good part of the engine that will have ground (alt bracket etc) and then pull a plug wire and crank it over while holding the tip of the test light near the coil pole, it should jump a spark out of the coil to the test light tip.

 

sounds like a cooked starter, Z06 corvettes are notorious for this happening.

 

He said it cranks over hard and fast or I would have said the same thing. I'm a tech and starters not starting when the engine is hot is a common thing, when they are on their way out.

 

very true i didn’t read into that fully.
My bad

 

If you can edit the tune, increase startup airflow adder a few g/s

 

Sounds like a good idea, should be able to confirm if this is needed by cracking the throttle open a hair while cranking. Don't hold it to the floor though, some systems go into a clear flood if you hold it to the floor and you won't get any fuel. Just apply about 10% throttle or so while cranking

 

First,
THANK YOU for the replies!
As stated she cranks just fine. I am familiar with heat soaked starters and this does not seem to be the case. She has a very strong spin when the key is turned.
I have done very little to trouble shoot since posting given the Easter Holiday and visiting family.
However, last night I fired her up, rolled her out of the garage maybe 30 feet and shut her down. Took about 5-10 minutes to unbolt the hardtop and put towels between the top and paint.
I fired her up ( no issues) , rolled her back into the garage and under the hoist for the top and shut her down. 5-10 minutes to put the harness on and lift the top straight up. Went to fire her up again to go for a drive and no fire. She turned over perfectly but no fire. She did have a smell of gas though so being flooded sounds like a possibility.. I waited another 15 minutes, she fired right up, I went for a drive, she ran GREAT, I came home and put her away.

If I remove the air cleaner and give a tiny bit of throttle next time she fails to start, maybe she'll get more air and fire up?? I do not have the ability to change the tune at this point.
IS there a recommended software package and cabling that I should get or am I better off finding a tuner in the North of Seattle area?


Again, your input is greatly appreciated!
Scott

PS: Other than the won't start after running issue the motor seems great! my car is now extremely quick to the point the happy pedal is almost a scary pedal! LOL!

 

Sounds like you're losing spark if you can smell fuel, or it could also be no air is getting in.

But if this problem occurred out of nowhere it shouldn't be the tune that's a problem. So I would clean the throttle body (they get dirty and sometimes cause issues starting and or idling low or stalling). If that doesn't get it done try swapping the crank sensor and see what happens.

You said you just finished installing the engine. Is everything new like sensors, plugs, throttle body etc?? If so and it's always been a problem (not started out of nowhere) I would lean more towards the tune being the issue.

 

Yes, Everything is brand new. The motor is a GM Crate with all new everything except starter however I bought that new also. It came as a "Connect and Cruise" kit including the GM computer, wiring, 4L75E transmission and computer all new. Basically driveline to radiator is all brand new. She starts perfect on initial start up. Drive a bit, shut her down and she will not start for 20-30 minutes.

I've had zero issues with the motor other wise.

HOWEVER . . . . . .
The steering was also replaced with a brand new rack and pinion. The idiot who did the install, I'll not mention my name so you won't know who it was . . . reversed the power steering hoses. The rack blew her gaskets in short order spewing power steering fluid EVERYWHERE like running water. What a mess that was! Yes I have since used MAF cleaner on the sensor just incase.

I am now wondering . . . . if the engine is showing signs of being flooded after startup, is there a possibility I plugged the air cleaner up badly enough with power steering fluid causing a low volume air issue?
The bluethooth dongle and software show no codes being thrown. I trust the reader works well as I have used it on my PU with twin turbos and it reads everything there including boost.

Again, the input is greatly appreciated and do not assume I know the little things. If it is dry tonight, I'll get her out and take the air cleaner off for a quick run and see what happens.
I have a small attached garage so running the car inside is not good and it seems to rain a lot North of Seattle so I have to wait for a weather window to play.

Thanks!
Scott

 

Ok,
tonight I had some dry weather and time to play.

long story short it seems when I shut the engine down and go for a restart the timing is advanced to 9 or 9.5 degrees. If I do not touch the throttle it will crank and not start. If I press the throttle to 15% she fires up!

on cold start the timing is 6 degrees and she fires up.

Does this make sense to the experts?

Thanks,
Scott

 

Cracking the throttle lets more air in. The fact it starts right up shows you need more airflow on startup.

Since you've put the motor in, have you let it set and idle for about 10 minutes? If not do that, if it's an auto also let it idle in gear for about 10 minutes. Your issue could just be that it needs to fully idle learn.

If that doesn't work a tune adjustment should take care of it.

 

I have a 1970 Camaro with this same setup and I am having the same problem. Went through the basics first. Found 10ga wire with self tapper used for battery ground to body. replace with 1/0 cable and grounded to frame. installed new ground straps for engine and trans to frame. replaced starter, wrapped headers and installed heat wrap on starter. Got car tuned, and I am still having the problem. The tune that was in the car was way out of whack. Fuel was maxed out at idle and running very rich, and way to lean at higher RPM. Now after the tune and new starter if I run it to operating temp, shut it off and try and restart immediately it will start. but if I go inside a store of eat food and come back it wont. The car has about 1,900 miles on it. Bought it a few months ago at Barrett-Jackson in Arizona. It seems like someone started to put a lot of money into it and then rushed the rest to get it to auction. I have fixed most of the crappy work that was done by the previous owner. but this crank no start is killing me and I cant really take the car out anywhere unless its going to be parked for an hour before I leave.

 

Welcome to my heartburn! LOL! You describe my issue perfectly. I thought I had a possible way to get her to start but yesterday proved me wrong. I drove her to work with no issues.Went to lunch and ate there. Time to leave and she cranks perfectly but no fire. 45 minutes of wait with periodic failed attempts to start, she fired right up like nothing was ever wrong. Back to work no issues. Time to go home? Not a problem! She fired right up and we went home together!

My next thing to try is to use one of those cans of air to clean keyboards. I will use the air to try to cool the MAF since it is easy to get too. It is the only thing I can see changing while sitting and waiting. The air intake
temp. One added thing I have confirmed is to hook my timing light around the plug wires and it shows spark while cranking.

Please keep me updated as to what you do or try and I will do the same. Between us, SOMETHING will be found.

Thanks
Scott

 

Your throwing mud at the wall at this point.

You need to hook up equipment and or take it to a tuner to see what is really going on.

But if you want to try a few more things you can try this..

Next time it wont start pull the hose off the brake booster and don't touch the throttle and see what happens.

If that doesn't do it turn the key on for 3 seconds then off for 3 seconds then on repeating this a few times. If it cranks right up after that that will indicate that you needed to prime the fuel system first. However, if that is the case you should have the worst issues after sitting over night.

 

I am happy to give that a try.
After pulling the brake booster vacuum line, there would be a vacuum leak and crappy expected idle. Is that what you want me to try?
Or, should I plug the vacuum line to avoid the expected leak?

I will not be able to do it tonight but tomorrow looks promising.

. . . . and yes, I feel like I am tossing mud at a wall . . . .

Thanks!
Scott

 

the point of pulling the vacuum line is to get more air in while cranking, yeah it will have a leak but what you need to know is does getting more air in make it start right up. If so then you know what you're chasing. If it fires right up go over and plug the hose in right after it starts running.

 

Got it, Thank you for the clarification!
I will try and get to it tomorrow!

Scott

 

LIfe got in the way again.
I hope to get back at it tomorrow evening for a while.

A couple of things I have to try.
First warm her up with a 15- minute drive.
Come home and let her sit turned off for about 5 minutes.
Confirm a no start situation.
pull the vacuum line off my brake booster to allow intentional vacuum leak and test for start. Make notes and come back here.
I also picked up a fuel pressure gauge and will hook it up looking for fuel pressure issues. Concern was noted the blue tooth dongle might not be accurate.

So that is my Friday after work plan. That is unless my bride comes up with more fun plans! LOL!

Again ALL input is appreciated!
Scott

PS: I did drive her last Saturday and OMG she is quick!

 

Tonight took her for a drive. About 40 minutes to get her nice and hot. Well, up to temp anyway. I shut her down at home. Hooked up my new fuel pressure gauge and turned the key on. It reads to 100psi. It pegged as soon as I turned the key on.

maybe I need a regulator in line? Could this be the issue?

Scott