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Thread: 1990 TBI 350 refuses to start and idle nicely, I have log files.

  1. #1
    Carb and Points!
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    1990 TBI 350 refuses to start and idle nicely, I have log files.

    So, I have tried everything on this truck before getting a cable, and now I have logs of this stubborn thing refusing to work. Im a newb and would love some other folks to look at this with me.

    Fresh tune up, IAC, New map sensor, TPS, temp sensor, and vacuum leaks have been checked and fixed. I have a second complete throttle body with brand new injectors that hasnt given me any better results. Im not having any luck at all.

    During these logs you can see me attempting to adjust the idle speed. All tests were at 0% throttle. To simplify the diagnostic I wanted to keep it in closed loop so during one test I unplugged the O2 sensor. The software reported the TPS at 15% so I attempted plugging in the new TPS without installing it, where it began reporting a negative 12%. You can see this in the log. My final test was to use a different ECU.

    My goal is to get the truck running well enough to give it to my sister. I have access to a Moats Burn 1 but I have never fussed with custom chips yet. I would love any input you have.

    Link to Log files hosted on GitHub.


    If you are not used to downloading things from Github, here is a photo showing how to download it. Click "Clone or Download", as shown in the photo, then "Download as zip".
    Last edited by The_Joe; 02-25-2020 at 08:48 PM.

  2. #2
    Carb and Points!
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    I guess my links didnt work, epic fail on my part. I have fixed my previous post and re-uploaded the files to github.

  3. #3
    Electronic Ignition!
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    Start by checking all fuses under the dash. Then check fuel pump relay under the hood behind the black plastic cover beside the coolant overflow tank. If all check good have some one crank the engine over and the other person spray a little carb cleaner in the top of the throttle body. If it fires up give it a couple more shots of carb cleaner and see if it runs for a little while. If it does you probably have a bad fuel pump. There are other ways to check that but if you don’t have a fuel pressure tester then the carb cleaner works good to. Don’t use to much. If it didn’t fire up then you probably spark issue. Bad coil or bad distributor.

  4. #4
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    Quote Originally Posted by GearGrinder View Post
    Start by checking all fuses under the dash. Then check fuel pump relay under the hood behind the black plastic cover beside the coolant overflow tank. If all check good have some one crank the engine over and the other person spray a little carb cleaner in the top of the throttle body. If it fires up give it a couple more shots of carb cleaner and see if it runs for a little while. If it does you probably have a bad fuel pump. There are other ways to check that but if you don’t have a fuel pressure tester then the carb cleaner works good to. Don’t use to much. If it didn’t fire up then you probably spark issue. Bad coil or bad distributor.
    Thank you for the reply!

    I have tested the fuel pressure and it is within spec, (I dont remember exactly but I could check) and with a bit of starting fluid the truck will start but it cannot hold an idle under about 2000rpm.

    Edit, I guess my title was confusing. I just meant that it doesnt start nicely, requiring starting fluid and such. I was unclear.

  5. #5
    Electronic Ignition!
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    Need a bit more info from your truck. How many miles? Is it a bone stock truck and no modifications? Has the distributor been pulled and reinstalled? Has the truck been sitting for a long time and was it running well when it was parked?Start by checking all connectors on the coil and distributor as the plastic over time gets brittle. I’ve seen a truck be hard to start and run like crap and die just like you describe only to find that the connector from the main wire harness to the coil pack. Just a guess but I would say you issue is with the distributor or coil or the connectors.

  6. #6
    Fuel Injected! brian617's Avatar
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    One of the most common TBI running issues is coolant temp sensor reading that is erratic. Log the temp sensor and make sure it looks normal. The fueling is heavily dependant on CTS. Examine pins in connector for corrosion.
    89 K1500 Scottsdale 5.7L 5spd 3:42

    Build specs: 97 4 bolt main block 350ci, Eagle rotating assembly with flat tops and 4 valve reliefs, Dart 165cc/67cc Iron Eagle heads, Manely SS valves and springs 110lbs seat @1.7, GM Ram Jet cam 196/206 @.50 .431/.451, stock intake and throttle body, heads and intake gasket matched, Delco EP377 fuel pump @ 22 psi, 427 PCM.

  7. #7
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    Quote Originally Posted by GearGrinder View Post
    Need a bit more info from your truck. How many miles? Is it a bone stock truck and no modifications? Has the distributor been pulled and reinstalled? Has the truck been sitting for a long time and was it running well when it was parked?Start by checking all connectors on the coil and distributor as the plastic over time gets brittle. Iíve seen a truck be hard to start and run like crap and die just like you describe only to find that the connector from the main wire harness to the coil pack. Just a guess but I would say you issue is with the distributor or coil or the connectors.
    Truck has 250,000 miles and is completely stock. Sis purchased it in the fall and it had a high idle and dying in gear issue that had led to it being parked for a while. I worked on it for a month and the issue was getting worse instead of better, then I gave up during the holidays and I'm just now getting back to it.

    Distributor was out when I did the intake manifold gasket, I checked the timing after and set it back to 0 degrees. It's possible that is having a connection issue, but I haven't been able to see any evidence with the timing light.

    Quote Originally Posted by brian617 View Post
    One of the most common TBI running issues is coolant temp sensor reading that is erratic. Log the temp sensor and make sure it looks normal. The fueling is heavily dependant on CTS. Examine pins in connector for corrosion.
    That was the first thing we did on the truck, and in the logs it looks fine to my eyes.

  8. #8
    Electronic Ignition!
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    Hmm. 250k on the mileage. Pull that distributor and junk it. Normally I would say go back with a good one but an engine with 250k on it I would go back in with a cheapo from your local auto parts dummies. I couldn’t get my 89 truck to pass emissions until I put a cheapo distributor in it. That same year I blew a head gasket in it ��
    Did you change the coolant temp sensor on top of the intake or the one in between number 1 and 3 spark plug. I’m sure Brian617 was referring to the one on top of the intake as the one by 1 and 3 spark plug only shows the temp on the cluster.

  9. #9
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    Quote Originally Posted by GearGrinder View Post
    Hmm. 250k on the mileage. Pull that distributor and junk it. Normally I would say go back with a good one but an engine with 250k on it I would go back in with a cheapo from your local auto parts dummies. I couldnít get my 89 truck to pass emissions until I put a cheapo distributor in it. That same year I blew a head gasket in it 😞
    Did you change the coolant temp sensor on top of the intake or the one in between number 1 and 3 spark plug. Iím sure Brian617 was referring to the one on top of the intake as the one by 1 and 3 spark plug only shows the temp on the cluster.
    I have another 350 tbi parts truck that is running well and I could barrow the distributor for testing.

    I'm not at the truck until this weekend but I'll give it a shot.

    And as for the sensor, yeah I got the one near the Tstat.

  10. #10
    Electronic Ignition!
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    Double check all grounds!!! One from the fender to the negative battery cable and of course the negative battery cable itself. One by the charcoal canister on the core support. One on the backside of the passenger side head to the firewall under the AC drier. Another one that runs from the frame to the firewall under the AC drier. Those last 2 on the firewall attach on the same stud sticking out from the firewall. Some models have one that runs from the frame to the block off plate under the ac compressor beside the water pump inlet. Another beside the ALDL connector under the dash screws to a price of sheet metal. Another bolted to the frame on the drivers side by the rear bumper brackets. One more by the gas tank door that bolts to the bed and the last one is under the bed coming off your fuel pump bolting to the frame. I wouldn’t worry about the fuel pump one though if your fuel pump is working and running at the correct psi then that ground is good. I think that covers all the grounds.
    Last edited by GearGrinder; 02-26-2020 at 11:46 PM.

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