Hi Tadge
i just found this section and have a question.

I recently installed a connect and cruise LS7 4L75E combo in my 69 convertible.
All seems to run and drive well with one exception.

She cold starts every time without hesitation. Seems to dive and run great.
However she will not warm start. Once cool, she fires right up.

using a Bluetooth dongle and iPad, fuel pressure is 57.9 lbs, air intake temp 120 degrees F , coolant 198F.

no start.
i’m letting Her sit for 30 minutes and am confident she will fire right up. I have used MAF Clean to clean the sensor and no help.

I am a rookie car hack with no idea what to do now. Assume I know nothing and offer any ideas you may have!
thanks in advance!

Scott

 

Just a guess, could be starter heat soak.

 

Thank you Ntfday,,
I failed to mention in the first post that she turns over just fine, she just does not fire. Would that be a symptom of heat soak starter?
One thing I have done was thinking maybe there was a voltage drop because my battery was long in the tooth, was to replace my battery with a much higher than 600 cold cranking amps rating.
minimum 600 is required for a 2013 Z06 so I went to interstate battery to get a stronger battery.

I also removed the MAF and used MAF cleaner on it in hopes of that being the issue.

I can hear the relays in the fuse block energize when I turn the key.

I guess my next step is to jack her up and look for any wires that may have been cooked. O2 sensors, crank position sensor, etc.

I do appreciate ideas and if the heat soak idea is still on the table, I'll get some wrap of some sort and give it a try. Otherwise a high torque mini starter might be on the table.

Thanks
Scott

 

Slow cranking is one indication of heat soak. What are you running for ignition?

 

Then engine is a complete crate motor LS7 from GM. All parts are GM new. The wiring is the GM hotrod connect and cruise wiring with various uneeded items dissabled for example the keyfob stuff. It included the computer and connections for the tranny.

Scott

 

I don't have a lot of experience with computer controlled engines, I'm 75, but heat is the enemy of anything electronic. That being said the location of the computer, IMHO, becomes paramount.

 

Engine computer is inside the car under the passenger side dash.
The tranny computer is under the hood and was rated to be there.
Thanks for the ideas though!


Scott

 

Hopefully there are others here that have experience with your problem as I am out of ideas other than I believe it's heat related. Be sure and check the simple things such as grounds and possible frayed wires and any wires to close to a heat source such as headers. As wiring heats up it's resistance to current flow increases.

 

On my LS swaps I've never had a heat soak starter problem. I always use the tin heat shield on the starter solenoid. Never bought a special mini-starter for a LS just stock rebuilt units. Even my 427 LS build.

Failure to start when hot almost has to be a sensor failing as the engine warms up. Crank sensor or cam sensor? If either is failing when warm your engine will crank but won't start. Also make sure they are fully plugged in. Cam sensor not so bad to get at but the crank sensor means pulling the header and starter.

Pull a spark plug and see if you have spark when starting warm? Be careful those coils put out a bunch of voltage.

When you turn the key to "on" when the car is warm can you hear the fuel pump turn on for a few seconds and then turn off if you don't turn the key to start? Just proves power to fuel pump is working correctly. External fuel pump or intank?

I haven't used a blue tooth to read the OBD2 but how does the ECM know what you have for fuel pressure? I haven't used the GM connect and cruise harness but the aftermarket harnesses I've used (Speartech and Howell) don't have any sensors to determine fuel pressure. Have you checked the fuel pressure at the fuel rail when warm?

You might post your question over on LS1tech. Those guys are good at helping out.

 

Thank you for the reply 71_Vert_LS1 !
Yes, I am leaning away from heat soak for now as she cranks just fine.

I like the sensor issue idea. Yes the crank sensor is a bugger to get to. I will get the car on ramps and check that the sensors are plugged in and wires not burned by headers.
Have to wait for a dry day though, my garage is not big enough.

I can also check the plugs!

When I turn the key on I can hear the relays clicking and the fuel pump coming on, then turning off if not started.
The fuel pressure is reported via OBDII interface and displayed on my IPhone. I have no idea how or where it is measured. It is clearly listed though and changes slightly.
I have not hooked a mechanical gauge to the fuel rail.

FYI I had fuel pressure gauge on my previous Ramjet motor for about 30 minutes. It filled with gas then leaked raw fuel onto the manifold. I'm lucky I did not lose my car that day and have not used one since. I am however open to a suggested pressure gauge that is of higher quality and testing the rail pressure.

I have posted on the LS1tech.com sight in the gen 4 section. Hopefully I'll get a response there too.

Thank you very much for your reply and suggestions!

Scott

 

I'm thinking you can "borrow" a fuel pressure gauge at the chain auto parts stores. I've never installed a permanent fuel pressure gauge on the fuel rail.

I still struggle with how the blue tooth can determine fuel pressure. I can't think of any part in the typical LS fuel system that includes a sensor that feeds back to the ECM.

Now this is a bit out suggestion wise but it happened to me with my E36 BMW LS swap. Similar to your problem. I would drive the car for awhile and it was great. Shut it off and then restart while warm and it would stumble a bit and then run fine. After a time it maybe a month or so it would just quit all be itself. It drove me crazy. Checked all the sensors. Replaced the crank sensor and cam sensor. Still did it. Then one day in the shop as I was looking for anything I thought was causing the problem I smelled melting plastic coming from under the dash. The fuse block for LS swap harness is mounted under the dash. I started to look around and come to find out the 12 volt constant wire for the ECM in the fuse block was loose and over heating enough to loose contact. Got hot enough to melt the area around the connector in the fuse block. I pulled that wire out of the fuse block and added a in-line fuse and everything has worked great ever since. Might want to check the fuse block wiring to make sure everything is good.

 

Gas cap issue. Loosen the cap. Rubber gas lines collapsing? Sounds dumb, but it starts after sitting for 30 minutes. Sim-le things first as it does run.also check your connectors, make sure none of them are loose or not fully seated. Any codes? We need pictures too.

 

Yeah I was thinking gas cap too. How is yours vented? I ran a vented cap and vented the tank via the bung on the tank that normally ran to the charcoal canister.

 

I use a vented cap, stock on 78, internal fuel pump.

 

Thanks for all the ideas!
I'll certainly check the gas tank vent. It was purchased specifically for the swap and does have a dedicated vent. Maybe that is buggered up.
Tomorrow is supposed to be nicer maybe I'll get to drive her in and when I get to work I can open the gas cap and then see if she starts,
I can also crawl under her and check connections and wires tomorrow.


FYI there are no codes being shown on the blue tooth interface.
Scott


Saturday I move my fathers C5 to my brothers house. Things are tight at the moment,

Scott

 

Pictures!

 

This , plus with the hot engine not firing , we had a similar problem here , mainly with the v6 GM engines , one way that worked was to pour cold water on the crank sensor , which on the v6 was at the front of the engine .Used to work so you could get the car home and replace it. Found it by googling "starting problems with V6..... '. MIGHT be relevant to your problem

 

Compression, ignition (at the right time), fuel (proper ratio WITH air) are the 3 things needed.... so.... whats missing? You said that during the warm NO start condition the engine cranks normally. You can hear the fuel pump prime but have not actually verified fuel pressure, and you don't yet know if there is or is not spark present when it will not start. Compression is usually not a consideration especially with a new engine. Fuel can be a concern if pressure is too low and can also be a problem with the percentage of ethanol. Spark, if not present, can be caused by a few different things, and as stated previously, I would look at the crank sensor signal (if it was in the shop and I knew it had no spark). One thing I have seen, is a throttle body that has not been calibrated on some cars can cause a warm no start condition. Try pushing down on the gas pedal just a little bit when it doesn't start. The engine may not be getting any or enough air to allow the engine to start and run. If fuel pressure and spark are confirmed and it still doesn't start while opening the throttle slightly, you really need to have a decent scanner hooked up to the OBD2 data connector (ALDL connector) to get info from the computer. HTH

Woody

 

Final resolution!
I checked the fuel pressure at the rail and found I was way OVER pressure. Literally pegged my gauge the read up to 100PSI.

LS Fuel pressure regulator added to the system near the tank resolved the starting issues.
Speedway Motors was very kind and sent me the correct part!

After install, all my starting issues were completely resolved!

Thanks for everyone's input on this thread!

Scott

 

Scott,

Thanks for the update.
Glad to here you found the problem.

-Chris