Hi, I recently installed a howell tbi system into my amc 360. I am running an msd ignition and they put the resistor in the harness for me. My problem that I am having is after it runs for about 15 mins then the idel starts to roll. It will fall down to 500 rpm and then back up to 1200 rpm and then it keeps doing this. If i rev it it does not bog until it comes back to regular idle. If I turn it off and start it up again then it goes away for another 10 min and then starts up again. Does anybody have any ideas as to what has caused this. Any help would greatly be appreciated.

Hi, I recently installed a howell tbi system into my amc 360. I am running an msd ignition and they put the resistor in the harness for me. My problem that I am having is after it runs for about 15 mins then the idel starts to roll. It will fall down to 500 rpm and then back up to 1200 rpm and then it keeps doing this. If i rev it it does not bog until it comes back to regular idle. If I turn it off and start it up again then it goes away for another 10 min and then starts up again. Does anybody have any ideas as to what has caused this. Any help would greatly be appreciated.

sounds like it's lean or has a vacuum leak.

Make sure the intake valley pan is completely sealed, and then you can adjust your fuel mixture by increasing your fuel pressure by 1 psi increments. Put a 0-20 psi fuel pressure gauge in line so that you can check to make sure your pressure is within specs.

One other thing you need to do is make sure your TPS voltage is within specs with your idle speed set to where you want it.

Some basics... Do you have a SES (check engine) light ? yes- see what code(s) you have... Check your howel manual (or get one) and see what base timing the ECM is set for and make sure that your engine is timed right (you will have to unplug 1 wire on the engine to set the timing)

All your sensors hooked up ?

Start there first...

Yes, I have a check engine light set up and there are no codes. I have base timing set at 10 degrees advanced. But I am not running the electronic distributor that the computer controls, I am running a pro billet MSD distributor. Do you guys think my timing is too far advanced. Howell never mentioned anything about that. I was also told to put in a tach adaptor. I will be checking the idle air and the TPS for proper voltage. Any other suggestions would be great.
Thanks
guys

My howell system did the same thing on my 258 and I discovered i had a vacume line in the wrong place on the manifold. I can't remember which one it was but i think the manifold has two different vacume ports. One has constant vacume and one the vacume increases as you raise the RPM's. You need to put the vacume line on the constant vacume. Call Howell.

Thanks guys, I will look into this stuff and see what happens. If anybody has any other answers that were missed here please let me know, and I will let all know hat happens when I diagnose what I have found out already. Thanks again.

Cheers

I had the same set-up as you and it did the same thing. It seemed it was trying to idle too low, then try to catch up before it stalled. Always did it at warm idle. I finally got a smooth idle by turning the idle up with the screw on the throttle body that opens the throttle up a little. Got it settle at about 750-800 rpm idle.
Side note, I ended up ditching the MSD (whole system with the dist too); the box went bad, had to ditch the whole system to diagnose it. Went to DUI and never had a reason to reinstall the MSD (different Howell resister for HEI, had to change it). MSD tech sucks.

One other item to check is your battery voltage. Make sure you have a good solid battery feed to the system and that you battery and altinator are in good shape. If your voltages drops down to around 12 v at idle, that could create problems. It's my understanding that the Howell like at least 13 volts for proper operation.

Thanks to all, I will be trying to resolve the problem this weekend with all your suggestions.

Sam

Thanks again to all. I will let you know what happens after this weekend when I try all the tips and tricks you guys have suggested.
Sam

Thanks to all, I think I have solved the problem. There is a problem with the oxygen sensor, when I unplugged the sensor and took it for a boot, the problem was solved. It can be one of 2 things. I have not yet completely welded the bung in the exhaust, and this is causing problems, or the sensor is just buggered. Next week I will get the bung welded and plug it back in again and see what happens. Hope it will solve the problem and I don't have to get another oxygen sensor.