I have competed my LTX swap and am beginning to take it to work again. It is afterall, my daily driver. I have now had it stall after driving at highway speeds for 20-30 mins two times. It stalls when I get to an intersection after driving it for a good while. It stalls and will not start again. It only seems to do it in the afternoons, mornings haven't had the problem (yet). After it cools back down, it will start up and run again.

Some specifics. LT1 swap into an 84 Z28. I used the A/C relocation bracket from Browers and the coil is mounted on that. I have already swapped the ICM, seems to be the most likely culprit. YES, I used the grease on the heatsink. I cannot pull codes due to a data link issue (working on that). I am going to try to do the ICM cooling mod tonight and see if that helps. If not, I'm going to MacGuyver some weird cooling scheme, mabye move the ICM out of the engine bay completely???? Any other issues that it could be? engine is a fresh rebuild and only has about 100 mils on it. LT4 hotcam kit, 355 bore. I do have the CEL on, but again, until I can figure a way to pull codes, not much I can tell from it. Any help or ideas would be great.

 

Did you buy AC Delco/GM ICM? My old LT1 car would do the same thing if I used a crappy one from the zone or Advanced Auto. I used to carry a spare with me all the time just in case it failed. Mine would just die and would not start until I replaced the ICM with another good one. Once I swapped to a factory one I had 8-9 years of trouble free driving. Just an idea. Good luck!

 

Nope, an autozone one. I don't mind spending for the gm one, but I'm not completely sure that it is the problem.

 

Take it to autozone and have them test it a dozen times to heat the ICM up, to recreate the situation. If its not ICM I think its still ignition/ignition wiring related.

 

Could be a lot of things.

Might be fuel related. Fuel pump sound weird? Does the gas cap hiss when you remove it after one of these stalling episodes? If you don't hook up all the fuel stuff like the vent in the back near the tank or the charcoal canister up front then issues may arise.

Also, will it start if you floor it while trying to start it? If so, then that may be a IAC issue or other sensor. Maf, map sensor for example.

If you have a can of pressurized canned air (like what they use to dust off office equipment) then try turning the can upside down and spraying the ICM heatsink. Very cold air will come out which would cool the icm quickly.

 

Also do you have a set of Noid lights to check for the injectors firing when it does this? I would also say check for spark as well, but if the noid light does not light up chances of having spark are slim in my experience. Especially if it is the ICM.

 

ok, opti is new 50 or so miles, coil is new same milage, no hissing from gas cap, fuel pump only makes noise when priming and has pressure when I try to start it after stalling. I really think its the ICM in this situation, but I just swapped it. Granted it is from Auto Zone, but damn, really that important for it to be GM? I'll buy a GM ICM just for grins. If need be, I'll relocate the ICM to outside the engine bay and put a computer heatsink on it.

This only happens in the afternoon and will restart after cooling for 5-10 mins. Definately heat related.

 

Can I replace the ICM with an MSD 6A ignition box?

 

Ok, I moved my fuel lines away from the headers to rule out vapor lock. Today I drove it and it actually died while moving. I pulled out my old ICM, and plugged it in and it started right up. I think I am sure it is the ICM now.

Does anyone else use the bowersrodshop a/c relocation bracket? I wonder if it is part of the problem as it is powder coated and the elbow blocks some of the air flow from the fans.

 

I ordered the GM ICM and will swap it when it gets here. If that doesn't work, I'll move the ICM completely out of the engine bay. I can't keep stalling out I need my car to run RELIABLY.

 

Ok, keeps stalling. I have swapped to a GM ICM and done a modified ICM mod. Remember, I am using an A/C relocation bracket, so the ICM is no longer mounted on the head. I put 3 washers behind each bolt holing the coil bracket to the A/C bracket to allowfor air to pass behind for cooling. Then, in true MacGuyver overkill mode, I put a computer cooling fan directly on top of the ICM and heat sink to ensure that it cools. Still stalling after highway driving at stoplights.
I need to mention that I have my ECM wedged between the battery and the radiator. I wonder if the temp is having the ECM cut off?? I am hesitant to say it is the optispark because I just swapped it like 100 miles ago. I AM aware that just because it is new, does not mean it is not the problem.

So, in summary, still no method of pulling codes. (working on that) Having a thermal situation that stalls out the car AFTER highway driving at stoplights. Starts again after cooling. ICM has now been replaced 3 times and SUPER modified. Any other potential culprits?

 

Maybe your ICM has a bad ground, or there is a bad ground somewhere. Im sure its hiding in plain site, dont forget the easy things first.

 

Just because the fuel pump has pressure doesn't mean its enough pressure. I don't know if its been done already but I recommend buying(or borrowing from a friend) a fuel presssure gauge tester. See if it has enough psi on startup then also when the stalling occurs. Should be around the 30s or 40s. If the reading is showing wrong psi, then could be clogged fuel filter, faulty fuel pressure reg, leaky injectors, bad pump, etc.

 

al of the fuel parts are brand new (about 100 miles on them). Fuel pressure is about 45 psi prior to stock regulator. I run 2 fuel pressure regulators. the 1st is brand new AEM with aguge and then runs to stock FPR. Gauge is on AEM FPR. Reads about 45 psi at stall (normal). 1st FPR acts as step down to OE FPR. Even if fuel is getting low enough to cause stall, it's the failure to start until cooldown that is driving me nuts.

 

Read through this , other possible causes

http://www.ls1lt1.com/forum/lt1-%7C-...ease-help.html

 

Ok, a few updates. First thing is that it is still stalling at stop lights after a good 20-30 min drive. I thought it might have been vapor lock. So I moved the incoming fuel line from the frame to vertical behind the intake to avoid the headers all together. I drove it to work and it stalled in the morning. This is the first time it stalled in the morning. I needed to get gas anyway so I pulled into a gas station (or rather coasted). Filled it up and continued to work. It did stall immediately after filling up, but then made it 5 more mins to work.

I drove it home after work with no gas cap on after reading the link posted by Firebat (thanks for all of your tips btw). It made it all the way home without stalling. This was my first return trip without stalling yet. It has become a running joke for my friend who acts as a tail car for my tests. I have 3 theories on the successful run. 1. The removal of the gas cap made a difference due to allowing pressure to release from the tank (I have deleted my canister long before the swap). 2. The full tank, now bear with me, perhaps it is vapor lock after all. Not initially vaporizing, but when the fuel returns from the engine compartment to the tank I am sure it is hotter than in the tank. Maybe it is heating up over the course of the trip and making the gas in the tank hotter so it takes less to vaporize. Having the full tank would have made the process take longer (eg. Making it home without stalling). Or 3. Just dumb luck.

I am going to use a compressor to blow out my canister line to ensure it is not clogged. But I really think it may be the heating of the gas and vapor lock due to the return style system. I have 8 feet of braided fuel line under the hood and it is very hot under my hood due to the headers. I am trying to convert an extra fuel rail I have into an LS1 style "return less" system (just returns next to the tank). This should provide fuel at near ambient temps to the injectors and will completely rule out vapor lock.

Any ideas or suggestions? Am I completely crazy for trying to convert my fuel rail system?

 

Bump

 

UPDATE

I think I have finally fixed the problem. I replaced my Walbro 255 lph inline pump with an intank pump. I changed the tank to a fuel injected tank (for the baffles), but I don't think a car that was origionally carb'd would have to swap tanks. I put a new Bosch in-tank pump in and wired everything back up. No stalling. I think the issues was 2 fold. 1st was the inline setup. I was having cavitation and vapor lock. The gas does get heated in the return style system in the LT1. Having an inline pump places the fuel under vacuum. When under vacuum, it lowers the boiling point of the gas causing fuel to boil in the line prior to the fuel pump (cavitation). Since the fuel also lubricates the fuel pump, the bubbles from boiling would allow the pump tp heat up and make the effect worse. Once this process started, it would become a downward spiral.

The 2nd part was the fuel pressure regulator. I replaced the on rail regulator with a spare I had and now it runs much better. I am still having hard starts, but I think that is because the "newer" FPR is better than the other, but not 100%. I also noted that after a 30-45 min drive, it would bog down at WOT and not spin the tires. While this still needs addressed, it is not needed for daily driving. I have been driving it now for 3 days to and from work (22 miles each way) plenty of time to heat up and have been in bumper-to-bumper traffic for upwards of 30 mins, still with no problems. I ordered an on-rail FPR from Aeromotive and that should completely fix the entire situation.