Howell varying idle when warm and engine dies after hitting it hard

[bORGEL]

I have a AMC 401 with a 260 cam, Mallory ignition and Howell TBI. I had the same TBI on a AMC 360 and it showed much the same symptoms.

The engine starts right up when cold and idles fine. When driving it is fine with the exception that it sometimes dies, without stuttering, after I hit it hard. It fires right up after it without problems.

When the engine has warmed up the idle is fluctuating all over the place, presently varying between 1250-1350 RPM's (in Park) but sometimes goes much lower and the engine dies. I could not leave the engine running for long without it dying on me.

I have changed the fuel filter (I have two, one before the fuel pump and one after) and checked the sock in the tank and cleaned the IAC.

Do you have any advise on what might be wrong'

Many thanks,
Palli

[babywag]

bad MAP sensor?
vacuum leak

Those are the first 2 things I'd check.

[FSJ Guy]

If you're using Howell's system designed for a 360 on a 401, you will have problems with it leaning out.

But you said it did the same thing on a 360. Hmmm....

Do you have datalogging ability?

[autogatto]

For sure as you've been already told if you're using the same eprom calibration that you had on the 360 this setup on the 401 will not work. 304 and 360 share the same eprom calibration but the one for the 401 is different. And I would think that you would probably have injectors not big enough. (but I'll leave this to be confirmed or not to people that are more expert than me).

I had really similar symptoms to the ones you are experiencing over 10 years ago and it drove me so crazy that I came really close to taking the fuel injection out and put back my carb. But my case was a little different since I had built the kit by myself with really little to no knowledge. In my case the whole problem was caused by a wrong O2 sensor. Replaced the little [rule-violating language removed - consider yourself warned] my jeep has run like a champ ever since.

[Blake]

My Howell TBI on the stock 360 in the waggy also has a similar problem with the idle. When warm, it fluctuates. Otherwise runs perfects and has never died.

I kinda attribute this behavior is due to lack of setting up the initial system setup procedures on Bill's site here:

http://www.binderplanet.com/forums/showthread.php?p=345737#post345737

If I were you I would start with this.

[PlasticBoob]

Do you have datalogging ability?

x10!!!!

It's very easy to find the problem with the appropriate graph in front of you. These aren't carbs; things are much easier to troubleshoot here.

[bORGEL]

Thanks for the advice. I do have data logging ability but could not upload the log when Itried including it in my original email (got an error stating that theattachment exceeded the limit – even though it was zipped and only 19kb insize). Is it possible that the administrators of this forum have to allow me toinclude attachments?

I failed tomention that the EPROM is a new one received from Howell (Troy) who made itspecifically for this engine. He did say that the injectors where “big enough”(if such a thing exists!”) for this application and he did see from the log that the engine is at, or close to, “14,7 something” that meant it was receivingwhat it needed – if I understood him right.

Troy atHowell had recommended that I would drive the Wagoneer like this for few days,but I find it unlikely that it will heal itself – hence my post here.

[chef]

Having the same problem with my Howell, idles erratically, when warm or cold, it is rich at idle 108BML. It leans out when I stomp on it from a stop light, lean berween 3-4000RMP. I have sent Troy several data logs, I am on chip number 12. 360 with 9-1 comp ratio, porteds heads, stock pistons,edelbrock performer intake,shorty headders,"3"exhaust, cold air intake, DUI ignition. We have been tuning for a year, he is sticking with it though

[bORGEL]

I do feel that the break pedal is a bit sluggish so perhaps that would indicate a vacuum leak?

If that is the case, can something be assumed in regards to the source of the vacuum leak if the engine runs OK when cold and the breaks are sluggish ?

Tks,
Palli

[FSJ Guy]

If the brake pedal is hard, that would indicate problems with the vacuum booster. If the pedal is spongy, that indicates problems with the hydraulic system which is separate from the vacuum booster.

[bORGEL]

I followed the procedure of setting the IAC as per the procedure on binderplanet.com posted by Blake. The idle RPM was set at about 800 RPM but as the engine idle speed was oscillating, even with the IAC disconnected, it was impossible to set the RPM?s lower.

When I started the engine the day after, it was hard to get it going as it died for the first starts and when pressing the gas pedal it would choke. I got it running after few attempts but I still have the problem of the engine dying while driving ? particularly immediately after starting driving after briefstop (e.g. stopping on a red light).

The engine idled high while in Drive, even after warming up, but when I put it in Park it started lowering the RPM and the RPM's started oscillating.

I have removed one fuel filter so now there is only one remaining (between the tankand the pump) as per recommendation from Troy at Howell.

So currently I have all the same problems but now with lower RPM?s after the IAC calibration procedure.

I tried spraying Carb/TBI cleaner on all hoses and the base of the TBI without any change in RPM.

NB! I have now been able to upload the attachment showing a log I did this morning (tks to moderators).

Thanks,
Palli

Any further ideas on what the problem could be?

[Bill USN-1]

A couple suggestions.

1. Disconnect all vacuum connections and cap them except for the map sensor.
2. You have a map error in your log so you need to disconnect the batt or the ECM to clear the fault prior to the next log.
3. Your data cable is not setup properly. You are in 10K aldl mode. That means there is a resistor in the data stream making the ecm go to aldl mode.
You should only have the gnd to pin A and the data to pin E. Nothing else. No jumper to B and no resistor.
If you made the cable then you may not have followed the correct diagram like i have on the BP.
4. You are max rich at 108. So either the tune is pig rich or you have a vacuum or exhaust leak driving it rich. (see #1)
5. You should also save the BLM table along with the data log when done logging.

Edit: make sure the map is connected to the map port on the back of the TBI.

You also did not complete the initial setup procedures. The TPS is at 3.6%.

[FSJ Guy]

With the cable in "10K" mode, the IAC usually would stay wide open (145) on mine. I noticed that your IAC actually would go as low as 108 or so, but where your idle was rolling from 900 to 1,400 rpm, the IAC was wide open at 145.

See what happens without the cable in 10K mode. If you're not sure, simply unplug the ALDL cable and see if the idle still rolls.

[Bill USN-1]

ALDL mode sets the idle to a fixed rpm (1000 normally) as set in the bin.
It also adds timing (8*) as set in the bin.
I don't remember if it's for all aldl modes but it's easy to verify. Just use a jumper and then a 10k resistor.
There was also a 4.7k mode.

[FSJ Guy]

ALDL mode sets the idle to a fixed rpm (1000 normally) as set in the bin.

I have experienced this, too.