Engine Howell 4.2 TBI ongoing idle and WOT fuel issues with new system

[CJKen51]

Hello All, I have around 1 hour of actual drive time on my Howell TBI it ran "mostly" well to begin with and I was excited to drive it. Then, it just started leaning out and dying. Was towed home, by my son, that day. That was back in early June. Anyway, I've messed with this forever. The list of tests is a long one.
When I unplug the MAP sensor, it will actually idle. It idles smooth. Granted, it's rich and in a limp mode, which lines up with the service manual that was included in my kit. Plug the MAP back in and back to dying within just a few seconds. Here's the kicker: I've tried two different MAP Sensors. I also picked up an extra computer, since they were $95. Tried both of those and switched the PROM over, of course. I've talked to Troy, at Howell, 3 or 4 times now and I checked and verified everything he asked. Looking for a tip on anything else I could check. Thanks, in advance.

 

[Manic Mechanic]

What's your 02 reading? Also what's your IAC? (Idle air control)

 

[CJKen51]

Hello-
I tested "movement" of voltage O2 sensor in a vice with my torch. Moves between .3 - .9 which, I believe is good.
IAC - only tested with key "on", engine "off".
Lt Blue = 11.47v
Dk Blue = .391 mv
Lt Green = .4 volts
Dk Green 11..47 v.
I have not back probed the IAC while the MAP was unplugged... only time it will stay running.
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[Manic Mechanic]

I've not messed with Howell to much (not as user friendly as Holley sniper or ACES)

But the IAC should be giving you a reading between 1-3% during idle.

Does Howell have a handheld for tuning or diagnostics?

 

[CJKen51]

As far as I know, they do not have a hand-held. I can hear and feel it pulsing (the IAC) when you do a base idle test. That's about it. They give you an ALDL connector which has 3 wires. It's an 80's style OBD1. Engine trouble light, in the kit will flash codes. i.e. 22 or 33 etc.. The only time I've ever had a code is when I unplugged the MAP, which is to be expected.

 

[boney]

I'm not a deep knowledge base on these. I wish you were closer though, I have a BT connector for the ALDL plug and use ALDL droid to monitor my system (I've built a custom ADX streaming file if you need it). It's made by Red Devil River. Not that you want to spend money on that stuff right now. I've had a bad O2 sensor and a bad MAP sensor, but both would throw codes and effect the performance while it was running. Like when you D/C'd the MAP sensor.

The injectors should pulse. That's proper action. The IAC should be (relatively) constant. It should open to keep an idle and then vary in open-ness to keep it. It shouldn't be opening and closing fast enough to feel it, as far as I know. At least, that's not how mine behaves.

Make sure your throttle is closing all the way to the stop. The IAC should open at idle and close once you've revved up a bit. One of the guys I know around here was chasing idle issues for a year, and it turned out that the throttle was hanging open sometimes, and not others. The end of the shaft didn't clear (I'm working from memory) something mounted nearby. The IAC? Maybe the TPS. We caught it because the throttle position sensor would give different readings when we revved it by hand then let it settle. This was leading him to mis-adjust the throttle position sensor, and then get a poor idle every time the throttle closed all the way. Or conversely, a high idle every time it hung.

That's all I've got. I'll ask if he's got any other thoughts. He spent a lot of time chasing things for his issue, so he has a lot of knowledge on it.

In the meantime, Troy is your man.

 

[boney]

Ah yes: I remember now. The throttle position sensor is mounted on the valve cover side. It was mounted too close to the throttle body and it was binding with the throttle shaft. As a field repair, we moved the washers from under the screw heads to between the TPS and throttle body. Don't know if this will help you, but it's worth having a look at, I suppose.