Lack of power above 60 mph. - Off-Road Forums & Discussion Groups
Jeep-Short Wheelbase All discussion of short wheelbase Jeeps: CJ, TJ, YJ and JK

Reply
 
LinkBack Thread Tools Display Modes
post #1 of (permalink) Old 01-31-2007, 11:56 AM Thread Starter
Journeyman
 
Join Date: Mar 2000
Location: Spokane, WA USA
Posts: 115
Thanks: 0
Thanked 0 Times in 0 Posts
 
Lack of power above 60 mph.

I have complete rebuilt stock 258 w/ added Howell California TBI, Pace Setter Headers and RV1 Comp Cam 68-231-4, TFI coil and stock distributor and ignition module. Engine rebuilt and installed by a (then) local engine re-builders. All vac lines and timing set per Howell instructions. Engine pulls fairly strong at low rpm’s but flattens out and runs out of power at full throttle in the higher rpm’s. Engine runs rich at cold start-up with lots of black condensation out the tail pipe. At operating temperature tail pipe exhaust looks a little rich. Moved from California to Washington State and passed smog test with excellent tail pipe emission readings. (Not running rich) New cat and 2.5 dia. Muffler.

Any ideas to what to check? I was thinking of bumping the timing up from specified 8 btdc.

My older over 200K stock carb with the Crane HI6 CD ignition had more power!
GeCJ7 is offline  
Sponsored Links
Advertisement
 
post #2 of (permalink) Old 01-31-2007, 12:59 PM
 
Join Date: Nov 2000
Posts: 2,687
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: Lack of power above 60 mph.

There aren't any gearing issues are there? What rpm are you at @ 60mph?
TiminMb is offline  
post #3 of (permalink) Old 01-31-2007, 01:23 PM Thread Starter
Journeyman
 
Join Date: Mar 2000
Location: Spokane, WA USA
Posts: 115
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: Lack of power above 60 mph.

No, running a T-5 trans and 4.56 gears. 60 mph in 5th is about 2,500 rpm. 35" MT
GeCJ7 is offline  
Sponsored Links
Advertisement
 
post #4 of (permalink) Old 01-31-2007, 01:43 PM
 
Join Date: Nov 2000
Posts: 2,687
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: Lack of power above 60 mph.

Have you recalibrated your speedo? I run a T5, 4.56's and 33" tires and run around 2400 rpm at 60 mph. Engine issues aside, maybe you are going a lot faster than you think?

My 258 has reasonable highway power, but I won't go too fast, I don't like the way my jeep handles at over 70 mph. It will certainly pull to 4000 rpms strong in 4th gear. It can't hurt to carefully experiment with timing if you watch for detonation.

If I had a Howell system, I'd ditch that nasty looking adapter plate that comes with it. Two barrels going into a sharp tapering plenum going into the two barrels in the intake looks like a performance nightmare to me. The adapter should maintain constant volume and run smoothly into the intake's two holes imo. But you may have other issues.
TiminMb is offline  
post #5 of (permalink) Old 01-31-2007, 01:50 PM
I Might Just Know What I'm Talking About
 
JeepDawg's Avatar
 
Join Date: Dec 2006
Location: S. CA
Posts: 1,503
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: Lack of power above 60 mph.

Your gearing is fine....
My first guess would be fuel pressure/volume. The TBI needs a good supply and proper pressure of around 15PSI. I assume you added an electric fuel pump at the tank? Did you replace the stock fuel line? It is a bit on the small side.

BTW...for all the money you put into that engine, which I would estimate at at least $1600 for the rebuild + about another $1500 for Howell and headers...you would have been better off with a swap using a SBC....but that's my opinion....
JeepDawg is offline  
post #6 of (permalink) Old 01-31-2007, 02:39 PM Thread Starter
Journeyman
 
Join Date: Mar 2000
Location: Spokane, WA USA
Posts: 115
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: Lack of power above 60 mph.

Yes, I put way too much $$ into this. Long story….What’s a SBC (Short Block V8?)

I will need to check the fuel pressure. Stock fuel line (5/16’’)to inline fuel filter to inline fuel pump to TBI. Stock fuel line return (1/8’’) per Howell installation requirements.

When looking at the fuel spray pattern on the TBI it seems a little drippy. I wonder how fine the spay pattern needs to be and how is should look?

Thanks!
GeCJ7 is offline  
post #7 of (permalink) Old 01-31-2007, 03:04 PM
I Might Just Know What I'm Talking About
 
JeepDawg's Avatar
 
Join Date: Dec 2006
Location: S. CA
Posts: 1,503
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: Lack of power above 60 mph.

Drippy is not good.....it should be a nice conical spray...

What kind of fuel pump are you using?

SBC - Small Block Chevy
JeepDawg is offline  
post #8 of (permalink) Old 01-31-2007, 03:26 PM
 
Join Date: Nov 2000
Posts: 2,687
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: Lack of power above 60 mph.

The spray pattern should look like its coming out of a spray bomb, even at idle, just that its pulsing.

The pump supplies the force, the bypass built into the throttle body provides the back pressure to get it to around 14 lbs/psi and the return line is necessary to allow unrestricted return to the tank. Leve says the stock return line is too small. From your description it is, but that would cause too high of pressure, not too low.

I'd start by T'ing in a fuel pressure guage on the input side of the TBI unit and looking for proper pressure. Its also possible it has nothing to do with pressure and its the tbi unit's injectors dirty.

Pressure low? pickup clogged, fuel line leaking on input side, pump faulty, filter clogged, voltage to pump low, regulator in TBI bad.
TiminMb is offline  
post #9 of (permalink) Old 01-31-2007, 03:59 PM
Way Outta Control
 
Join Date: Sep 1999
Location: usa
Posts: 10,815
Thanks: 0
Thanked 1 Time in 1 Post
 
Re: Lack of power above 60 mph.

Back to basics --
First check the total timing advance - it should be about 35 degrees at 3000 RPM.
Then check to make sure the advance is about that 8 degrees at idle - vacuum connected!
The instructions probably say disconnect the vacuum to set timing - that's fine, but when you re-connect it at idle it SHOULD NOT CHANGE if it's the correct vacuum.

Howell has been sending throttle bodies out that do not have ported vacuum like the distributor needs to operate correctly. Last time I talked to them they had no idea of the difference between ported and manifold vacuum!

Either over or under advance can limit top end.
Remember - the people at Howell are are harness builders, not car people!

IF the timing is correct at BOTH idle and 3000, then suspect the fuel system, but do the timing check FIRST.

Do a search for "propane trick" - follow the instructions on adding propane at speed - if it helps, it's lean. It'll cost you about $9.95 to make the tool - simple. It's a very simple and easy way to tell if it's a lack of fuel.

If it is too lean, then suspect fuel pressure. Use a gauge right at the throttle body to check pressure.

Let us know what you find!
RRich is offline  
post #10 of (permalink) Old 01-31-2007, 04:14 PM Thread Starter
Journeyman
 
Join Date: Mar 2000
Location: Spokane, WA USA
Posts: 115
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: Lack of power above 60 mph.

Thanks, I'll take a look at what was said.

How hard is it and how do you clean the injectors?
GeCJ7 is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Off-Road Forums & Discussion Groups forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome