Howell TBI Acceleration Problem!

[jzak]

Hey Guys,

So i'm been having this issue since I bought my CJ and nothing I do seems to completely fix the problem. The Jeep accelerates great as long as you keep the gas peddle in a certain position. If i push the peddle to the floor the engine will start to sputter and die.

I have replaced literally every component of the fuel/injection system:

*Completely Rebuilt TBI Unit
*ECM
*Vacuum Lines
*Fuel Pump
*Fuel Filter
*PCV Valve

The only thing that i haven't replaced are the fuel lines and tank.

Since the TBI unit isn't factory to the AMC 258 i6 / 4.2l engine, i'm beginning to think that maybe this is just the way the injection system is, but i would love to get a second opinion.

 

[Posi]

Did you replace the parts you listed because they were bad?
What is your TPS set at? I set mine at 54.5
Do you know your block learn (BL) #? Should be within 10 + or - of 128

 

[Torxhead]

I would also think the problem would be the TPS, But a new preset one should come with the rebuilt throttle body. Some of the throttle bodys have a fixed tps and cannot be adjusted. Did you purchase it from Howell or somewhere else? Did you get any engine codes sent from the computer? A phone call to Howell's tech line would be a good choice.

 

[jzak]

Replaced everything over the past two years because I've been trying to find the cause of this problem.

New TPS came with the rebuilt TBI which was installed six months ago. I don't think my TPS is adjustable. It's just a plastic piece that's screwed into the left side of the tbi unit. There's nothing to adjust.

The Howell TBI unit was installed by the PO. There is a Howell chip in the ECM with all the presets for the vehicle. The chip has a sticker on it which says it's for a AMC 258 i6 / 4.2l CJ5 . I have never tried to adjust the settings on this chip, or know if you can.

 

[Torxhead]

Hopefully there was a Check Engine Light installed to possibly determine just what the issue is. Howell does have a website and a tech line to help you out. If you received any of the installation literature that was included in the kit that would help also. You could take it in to a fuel injection shop or try to do it yourself by downloading the installation manual from their website along with some internet research on a throttle body injection: Howell Engine Developments, Inc.

 

[Lumpy Grits]

Have you confirmed the fuel pump PSI to the TBI is with in spec? Not just at idle either--
When the fuel psi drops below a certain amount. The TBI won't 'fire' till the psi comes back up to a certain minimum psi spec.
LG

 

[jzak]

Cant remember the PSI on the Fuel Pump, but it was the one recommended by Howell.

I also think I may have to contact Howell, and get their input. This whole thing really hasn't been high on my priorities recently, because I've gotten to the point were I can position the gas peddle just right, getting excellent acceleration. I just wish I could slam on the gas once in a while without the engine dying on me.

Merry Christmas!

 

[Posi]

Check the fuel pressure as LG mentioned, if/when you call Howell that will be the first thing they will have you do.

I have a fixed TPS, to make it adjustable just elongated the holes. This is what i did to set it at 54.5

Edit: the BL numbers will tell you how lean or rich your engine is running.

 

[jzak]

Check the fuel pressure as LG mentioned, if/when you call Howell that will be the first thing they will have you do.

I have a fixed TPS, to make it adjustable just elongated the holes. This is what i did to set it at 54.5

Edit: the BL numbers will tell you how lean or rich your engine is running.

I installed the Howell recommended fuel pump a year ago, and it has made no substantial difference.

I think your Throttle Position Sensor is different from mine. I attached a photo to this post. Please show me exactly how i change the TPS to make those adjustments, because when you say, "elongate the Holes" and "Set it to 54.5," I got no idea what your taking about. If you could forward a link to a instruction page or video, that would be great.

Thanks!

 

[Posi]

Same one I have. There is more to it then setting the TPS, I'll post more after the holiday.

 

[Lumpy Grits]

Something else to think about-
Confirm your wiring to the FP. Those FP's for FI, pull a healthy amount of AMPS.
Your looking for voltage drop which slows down the pump.
Low voltage will also kill the pump over time.
What gauge wire did you use to wire the FP? Where is the power(+)lead coming from? How did you ground(GND)this pump?
Also-What dia(ID)is the fuel line? When was the last time you ck'd the fuel filter for crud?
LG

 

[Posi]

The pic below isn't great, but if you look closely you can see where I elongated both holes so I could adjust my previously non-adjustable TPS. Howell will tell you 5-7 is an acceptable range, but 54.5 is ideal.


There is two steps that should be done before setting the TPS, timing and IAC settings.
Before you attempt to set the TPS read below.

I have replaced literally every component of the fuel/injection system:

*Completely Rebuilt TBI Unit
*ECM
*Vacuum Lines
*Fuel Pump
*Fuel Filter
*PCV Valve

The only thing that i haven't replaced are the fuel lines and tank.

Other components in the fuel injection system that you didn't include in your list, IAC. O2, TPS, and MAP.

Since the TBI unit isn't factory to the AMC 258 i6 / 4.2l engine, i'm beginning to think that maybe this is just the way the injection system is, but i would love to get a second opinion.

Absolutely not, it should run flawless.


I always test any suspect sensor or component to confirm it's bad before I replace it this way I not wasting my money without solving the problem. All the sensors can be tested, even the O2 using a meter and propane torch. You can trouble shoot any FI sensor by doing a search on the net.


You have a choice, do the work yourself, or pay someone else to do it for you. If you call Howell they won't have any magic answers for you, nor will I. The best way is to start from the beginning with the process of elimination, it's the only way I know how to do it.


Start with a complete tuneup,
Check the plugs,
Ignition wires (check each wire for the correct specs)
Timing
Ignition (make for you have 6v at the coil with key on)
Fuel pressure
Filters
Vacuum test
Compression test


Once the above is within specs check for any ECM codes


Locate the Assembly Line Diagnostic Link (ALDL) typically under the dash below the steering wheel. With the key off, install a paper clip between A (ground) and B (diagnostic terminal) in the ALDL ((look closely they will be stamped A, B, first two slots, top row right). Turn key on, the engine light will flash 12 three times then any codes if stored.




Or you could buy an ALDL cable, and down load a free program to read your engine's performance


Just a random link you can make your own cable (I did) or buy one for less elsewhere.
OBD Diagnostics


Free program to read actual results

WinALDL - 160 baud ALDL reader


Using the reader with a laptop you can get documented engine output while your driving down the road.


Post your results.

 

[Torxhead]

Good info there Posi, thanks for sending in that pic. I could use some fine adjustment on mine setup also.

 

[Posi]

An alternative to enlongating the holes is finding an adjustable TPS and plug at the boneyard. I just like to use what I already have if possible.

 

[76cj7chick]

Hey, These guys are offering some great advice. Another thing I would double check is the rebuilt throttle body. Did you get it off line? I purchased several "rebuilt" throttle bodies a few years ago from an eBay seller but had seen issues you are currently having. I finally took the throttle body apart and the guy NEVER replaced/rebuilt the regulator diaphragm. In fact on all throttle bodies they had a used and many times torn diaphragm. Once I replaced that it ran better.
Double check your injectors that they are for the I6 too.

But if that is good, I would check what the guys are saying. Personally I would NOT adjust the screw for the TPS. It is preset at factory and should remain so.
If you have your old throttle body, double check the numbers on it match the rebuilt one.
Also, could check your MAP sensor. Make sure its within specs.

Just some more ideas.

One other thought... When ever you get a new/rebuilt throttlebody you're supposed to RESET the TPS needle. Unfortunately, I can't remember exactly how its done. I think you key the ignition on (but don't start the vehicle) then it should reset the needle. But double check on that.
Good luck.

 

[Posi]

Personally I would NOT adjust the screw for the TPS. It is preset at factory and should remain so.

It was preset at the factory, for “factory engines”. Since then the TB's have been rebuilt, and installed (in this case) on a AMC engine. When I purchased my Jeep it had howell FI installed, when I checked the voltage at the nonadjustable TPS it was 7.2v and ran crappy, once I set the timing, IAC, and set the TPS to .54 it ran great. Howell says 5v to 7v is acceptable, I say it will not run as it should anything above 6v. The TPS should be set at .54v, it will read 0.2% a digital screen if you have one, if it's over 2% it may never enter idle mode.

When ever you get a new/rebuilt throttlebody you're supposed to RESET the TPS needle. Unfortunately, I can't remember exactly how its done. I think you key the ignition on (but don't start the vehicle) then it should reset the needle.

No TPS needle, I think you mean throttle plate. You adjust the throttle plate with the IAC setup procedure. As I previously mentioned there are steps that need to be followed to set the TPS.


-Set Timing
-Set IAC
You need to put a jumper between pins A and B of the ALDL connector.
Turn the key on (not start) and the IAC should drive completely closed. You will normally hear a buzzing from the IAC, wait 30 seconds.
Now unplug the IAC connector. Turn the key off. Remove jumper. Start motor.
On the front drivers side of the TB is the adjustment screw. Use a T-20 bit to adjust the idle speed to at least 100 rpm less then your warm idle speed.
You are looking for the lowest consistent idle your motor will do. When set, turn off motor and reconnect the IAC.
-Set TPS
Loosen 2 screws and adjust as needed.

 

[gyvrr]

Very interesting post. I also have had issues with Howell injection. I've had a series of code 44 for a lean exhaust. The engine would lay down and flash the check engine lite. Then the lite would go out and the engine would revive. Later it would lay down again, but no light. This is on a single run up hill at about 35 MPH. I installed the Howell myself per their instructions. I've followed all their trouble shooting per service manuals provided with the kit. The Howell has been in place for about 5 years and other than this issue, I have been very happy with the performance. Now, with this info I'm looking into picking up the programs and another laptop. Wife not happy about using this one outside.

 

[Torxhead]

I think you guys with t.b.i. issues should know what fuel pressure you are getting into the back of the throttle body. The fuel pressure can be increased from the underneath rear of the unit. Providing the correct amount of fuel is at least getting the far. Fuel delivery can get complicated as the tank has to be vented and the fuel pump placed in the correct position. The plug that the Howell system came with from the pump is pretty weak and I would suggest removing. The fuel pump wiring came with #18 wires and that is pretty skimpy.

 

[Posi]

FYI, some have a tamper-proof security star screw, you would need a tiny T-10 security bit for removal. Chances are the screw will be frozen, and the small T10 will break if you put too much pressure on it. The one I had wouldn't budge the spring, so I drilled out, and tapped for a 1/4" 28 bolt (what I had handy). Made for an easy adjustment after this fix.

Not all have the security star screw.

 

[76cj7chick]

My bad! I meant IAC senor.

Its been a while since I had the howell wiring on my 76 CJ7 and AMC 258 i6 / 4.2l i6. So, I'm just trying to go by memory. Which is not the.most reliable.

If memory is right, I think the fuel pressure for the Howell is supposed to be 11-15psi max.
When I had my howell harness, I would get limp home mod only (and it always seemed over jetted). but it could be because it wouldn't go out if limp home mod as I didnt have the howell ecm and didn't have spark control with the harness.

If its nothing to do with the fuel pressure or delivery, it could it be a faulty ecm? Bad ground?
Also, there is a "needle" in the IAC sensor that closes when you key on the ignition but don't start. You may hear it resetting if you're near the engine bay with hood up. --you may even be able to see it in the throttle body closing. (I was able to see mine set)
But by the sound of it, it may not be the issue.
I agree with all of the guys. Check all of the volts and fuel pressure. Check to make sure no codes are being thrown.
Do you have the howell programed prom and chip in your ecm?