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Thread: 90 Corvette heat soak issue

  1. #1
    Carb and Points!
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    90 Corvette heat soak issue

    I have been working on a 90 TPI Corvette for 2 years now. I had originally posted a request for a tune file on this car as the owner had removed the factory failed engine and installed a ZZ4 crate engine, Edelbrock TPI intake, Holley 58mm throttle body, and headers. I was directed to contact David at Old School EFI, who did an great job tuning the car. Had it running better than factory in no time. I highly recommend David for any tuning needs. Great prices and very impressive skills. The owner drove the car about a year before it ended up having injector problems. Turns out a set of Python Injectors had been installed. I had worked with these back in the beginning of the import days and they would cost you an engine in no time flat. The injectors would get hot and the resistance would go nuts and they would stick open. I contacted Fuel Injection Connection and got a set of 22 psi injectors, David did another tune for it and the car ran flawlessly for another year. I believe the owner is averaging 1000 miles per year so it does sit alot. Now the car is back to acting up. The car had problems when warm idling. I pulled the TB back off and cleaned out the IAC passage and had noticed through logging the car that the IAC would stick so I installed a new IAC. Got the car to idle smooth at around 40 IAC counts. It has a non adjustable TPS but voltage is around .50 volts. The owner test drove the car for 25 miles and it did great. He left the next day and drove the car 35 miles, let the car sit for 2 hours and 20 miles into the return trip he got stopped for construction. The car started surging at idle and shut off. It refired after one try and he drove it another 10 miles until another stop light where it shut off and took 5 tries to start again. One more stop sign and the same results only this time when he went to WOT it acted like it was only running on a third of what it normally does and it set a code 44. I have installed an aftermarket aluminum radiator and a 180 degree t stat plus the fans come on at 190 and 195 respectively. I logged the engine when the car acted up and TPS percentage was smooth, CTS stayed right at 189 degrees at idle, and IAT's were 128 degrees. I have a brand new distributor, cap, and rotor coming for the car as the intake really traps the heat around the distributor. The car has an MSD box on it and I have blocked of the EGR and removed the air pump. The car has over 100,000 miles on it and it has the stock ecu. It is speed density and another thing to mention is if the car sits for 4-6 hours it will repeat the cycle all over. I am just looking for ideas. Thanks for reading.

    Sean

  2. #2
    Fuel Injected!
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    I really don't have much to add, but could the module in the HEI be going bad? Was it installed with the proper heat conducting paste?

  3. #3
    Carb and Points!
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    I have a new distributor assembly coming for it. Should be here this week.

  4. #4
    Fuel Injected!
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    Quote Originally Posted by sgtcjt71 View Post
    I have a new distributor assembly coming for it. Should be here this week.
    It could be the MSD box itself. I have run several of them without any issues myself but others have had issues.

  5. #5
    Fuel Injected!
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    Quote Originally Posted by sgtcjt71 View Post
    I have a new distributor assembly coming for it. Should be here this week.
    It could be the MSD box itself. I have run several of them without any issues myself but others have had issues.

    If the distributor does not fix it. Try bypassing the MSD as a test and see what happens.

    It could also be a weak fuel pump or even vapor locking. Weak fuel pump would prevent the fuel system from having adequate flow through the return system. The fuel flowing through the return actually cool the fuel rails.

    Finally I have seen fuel tank vent systems get plugged up from failing rubber lines and other issues. A fuel pump will have a very hard time pulling fuel out of vacuum even if it is in the tank submerged.

  6. #6
    Carb and Points!
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    I am removing the MSD unit as it was only put on to combat an overrich condition caused by running a ZZ4 on the stock speed density system and not tuning it. The vent idea is very interesting though as I had lawn mower doing exactly the same thing this Vette is doing. I converted the fuel cap to a vent style after reading your post.

  7. #7
    Carb and Points!
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    Found some things on the car. Found a fuel line sitting right on top of an intake runner. Evidently room was tight between the runner of the Edelbrock intake and the hose off the water line to the throttle body. I removed the water line and machined off the fittings. I also rebuilt the distributor with all new components including a gear from GM. I replaced the fuel pump, removed the MSD unit, and replaced the ecm so hopefully we get some positive results. Feel kind of dumb on the fuel line but I never seemed to get a clear view of the line since when I installed injectors I left the TB hanging so I didn't have to drain coolant and the same when I put the IAC in. I never removed the coolant line until the other day when I drained the coolant to fix a leaky t stat housing and run a new hose to completely bypass the TB.
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    Last edited by sgtcjt71; 07-27-2017 at 02:55 AM.

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