258 power loss - 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 03-24-2008, 10:53 AM Thread Starter
Journeyman
 
Join Date: Feb 2004
Location: Arizona
Posts: 155
Thanks: 0
Thanked 1 Time in 1 Post
 
258 power loss

Vehicle:
88 YJ, 258(maybe 30K on rebuilt long block), MC2100, "TR" ignition with HEI module.
Situation:
Loss of power during accelleration or when the gears shift(auto trans), my air/fuel gauge reads WAY too lean(when power is lost) but reads rich when cruising and at idle. The gauge also fluctuates from time to time, rich to way lean back to rich to slightly lean...etc.
What I've done:
Checked for vacuum leaks...over and over again...repaired as necessary. Set timing to 9-10*, gapped plugs to .035, higher grade gas, pulled distributor/cleaned/replaced. timed again...and again. checked curve...no change in timing from idle(700rpm)til about 1300rpm then jumps up til i cant see it, this occurs progressively until about 2500rpm or so. thats with ported vac connected...w/o vac connected, same thing but it jumps up about 4* and stops...thats the mechanical advance. I drove with and w/o vac advance connected, not much change. I've adjusted the diaphram on the distributor in and out...doesn't seem to help much.
I'm not going to blame the carb yet since the same thing happened when the weber was on there. From what I have read, mech advance is supposed to kick in from idle until about 1200 rpm, then vac advance takes over and should not bring timing above 35*. I've read, researched, asked you guys but still I'm missing something.
Your thoughts and suggestions are welcome...

'88 YJ
USMCYJ is offline  
Sponsored Links
Advertisement
 
post #2 of (permalink) Old 03-24-2008, 12:11 PM
Apprentice
 
Join Date: Oct 2007
Location: Amherstview, Ontario, Canada
Posts: 63
Thanks: 0
Thanked 0 Times in 0 Posts
 
with my hei im runnin .045 spark plug gap and timing about 10-12 degrees
markr1001 is offline  
post #3 of (permalink) Old 03-24-2008, 12:27 PM
Moderator
 
Jim_Lou's Avatar
 
Join Date: Dec 2001
Location: Belleville, Illinois
Posts: 11,485
Thanks: 15
Thanked 22 Times in 17 Posts
         
If it's running too rich and then way too lean, forget about the ignition sysem for now - it can't affect the mixture.

If it behaved exactly the same way before the Motorcraft carb, it must be related to the fuel supply or the air supply. Does it still have the stock air intake system? Maybe there's a flapper that's not operating properly. Or maybe the fuel filter is clogged, or the pickup in the tank is clogged, or the pump is old and not putting out enough pressure, or the line form the tank to the pump is rusted through and sucking air. Have you given the entire fuel system a first class checkout?

EVERYTHING's easy for the guy who doesn't have to do it.
B. Dash Fabrication
Jim_Lou is offline  
Sponsored Links
Advertisement
 
post #4 of (permalink) Old 03-24-2008, 12:32 PM
Way Outta Control
 
Join Date: Sep 1999
Location: usa
Posts: 10,815
Thanks: 0
Thanked 1 Time in 1 Post
 
Your advance isn't right, but I don't think that's the problem right now. We can address that later.

Please clarify - HEI but you say TFI also.
Does that mean you are using the square TFI coil triggered by the GM HEI module?

You said you have an adjustable vacuum advance - the distributor - a GM HEI? The original Ford? Or an aftermarket adjustable?

Is it just lacking power, or is it a progressively loss of power - like it's slowly getting worse?

If it is the remote TFI coil, check the coil wire - swap it with a known good one.
If it's using a GM coil - either in the cap or the square remote ones, look very closely at the ends where the core goes through the windings. Look for grayish marks - where the insulation is flashing through - looks like dried smoke. TFI coils can also do that.

It sounds like an ignition problem.

But to make sure it's NOT fuel related - do a search for "propane trick." Make the tool, do the test while driving. Make it lose the power where it should be more power - then add propane. If it gets better it's fuel, otherwise ignition.

And - check the timing chain for excessive slop. Rotate the crank BY HAND in either direction till the timing marks line up. Then watch the disdtributor shaft while turning it in the opposite direction - when the shaft barely moves, STOP. The difference between where yiou stopped and the original position is the chain's loosenes.
But that's only after you check the more obvious - usually when the chain loosens up you get a little more power bottom end, not less - since the cam's running retarded.

Let us know - and answer the above questions.
RRich is offline  
post #5 of (permalink) Old 03-24-2008, 12:55 PM Thread Starter
Journeyman
 
Join Date: Feb 2004
Location: Arizona
Posts: 155
Thanks: 0
Thanked 1 Time in 1 Post
 
Stock intake...and...flapper???
Fuel pump is maybe a year old...pressure is good. haven't checked the fuel system before the pump but everything after is good...filter, lines, etc.

HEI module only...tfi coil only...sorry bout that. original fomoco dist.
went to lowes for the parts for the propane trick...they were closed last night at 6. no slop in the timing chain but i will re check tonight.
lots of frusteration...probably gonna be one little thing that i have missed.
thanks

'88 YJ
USMCYJ is offline  
post #6 of (permalink) Old 03-24-2008, 01:21 PM
Way Outta Control
 
Join Date: Sep 1999
Location: usa
Posts: 10,815
Thanks: 0
Thanked 1 Time in 1 Post
 
Is it just lacking power, or is it a progressively loss of power - like it's slowly getting worse?

The propane's going to eliminate - or tell you that it's fuel.

If equipped, EGR disconnected? Valve is totally closed? Just disconnecting vacuum doesn't insure it's closed all the way.

Flapper - moves freely?
Exhaust sounds normal at the tailpipe? Often a plugged exhaust makes a hissing sound.

Vacuum reading - idle, unloaded, loaded, and when it's faltering?

Check that coil wire! Progressive getting worse could be the end inside is wearing away - not always visible.'

Check the spark itself at a plug - put a Phillips head screwdriver in the plug end of the wire. Hold the blade close to ground while running - it should be a crispy bright blue spark. Rev it up to make sure it stays the same.
A bad coil will make a red wide hissing spark.

You did eliminate the ignition resistor - running a full 12 volts to the module (+) AND coil (+).

As you said, probably something stupid, just hard to find.
RRich is offline  
post #7 of (permalink) Old 03-24-2008, 05:32 PM Thread Starter
Journeyman
 
Join Date: Feb 2004
Location: Arizona
Posts: 155
Thanks: 0
Thanked 1 Time in 1 Post
 
Quote:
Originally Posted by RRich View Post
Is it just lacking power, or is it a progressively loss of power - like it's slowly getting worse?

-same loss of power at the same time each time...doesn't get worse or better. With consistent pressure on gas pedal, the air/fuel gage will read rich then way lean when the transmission changes gears. The same thing happens under acceleration but eventually goes back to rich once the engine catches up with the speed<<<possibly not worded right.

The propane's going to eliminate - or tell you that it's fuel.

If equipped, EGR disconnected? Valve is totally closed? Just disconnecting vacuum doesn't insure it's closed all the way.

-EGR not used, port plugged and sealed, will check for a leak there too.

Flapper - moves freely?
Exhaust sounds normal at the tailpipe? Often a plugged exhaust makes a hissing sound.

-sounds normal as applicable to an engine running rich...no hissing. new muffler as of last year. cat is free flowing, its actually "fake", no honeycomb.

Vacuum reading - idle, unloaded, loaded, and when it's faltering?

-not sure yet, will check with vac gage.

Check that coil wire! Progressive getting worse could be the end inside is wearing away - not always visible.'

-will check/replace if needed but its had these symptoms with the old 258 that i replaced a few years ago...nothing has changed...as far as this issue goes anyway.

Check the spark itself at a plug - put a Phillips head screwdriver in the plug end of the wire. Hold the blade close to ground while running - it should be a crispy bright blue spark. Rev it up to make sure it stays the same.
A bad coil will make a red wide hissing spark.

-not sure of the process you speak of here, please clarify. how do i put a phillips head (assuming you mean flat head) screwdriver in the plug end AND put the blade to ground...wouldnt the blade be in the plug wire?

You did eliminate the ignition resistor - running a full 12 volts to the module (+) AND coil (+).

-haven't tested the actual voltage but i've got the module relayed to the battery.

As you said, probably something stupid, just hard to find.
Like I said before, the same problem I am having with this engine, occured with the engine I replaced, so I am assuming it's external engine components. I did not replace the old components with the engine, except the fuel pump. Thanks again. off to lowe's to get the propane trick materials.

'88 YJ
USMCYJ is offline  
post #8 of (permalink) Old 03-24-2008, 05:34 PM Thread Starter
Journeyman
 
Join Date: Feb 2004
Location: Arizona
Posts: 155
Thanks: 0
Thanked 1 Time in 1 Post
 
sorry bout the above post i made. first time using the "quotes" in a post. my replys to what you wrote start off with a dash.

'88 YJ
USMCYJ is offline  
post #9 of (permalink) Old 03-24-2008, 06:53 PM Thread Starter
Journeyman
 
Join Date: Feb 2004
Location: Arizona
Posts: 155
Thanks: 0
Thanked 1 Time in 1 Post
 
for the propane trick, it says use the smallest size drill bit i have to drill out the hole...smallest size i have is a 2.5mm, seems too big to me. Yes, no?

'88 YJ
USMCYJ is offline  
post #10 of (permalink) Old 03-24-2008, 08:53 PM Thread Starter
Journeyman
 
Join Date: Feb 2004
Location: Arizona
Posts: 155
Thanks: 0
Thanked 1 Time in 1 Post
 
Found a leak at the throttle shaft...kinda expected that one...and another one at the base gasket...kinda expected that one too. I used my new vacuum leak detector...the "propane trick". replaced the coil wire. the old one had a little corrosion on the connectors at either end.
Now is the fun part...
I had posted a while back about my throttle shaft being loose and the fix would be to re sleeve it. I'm all about doing things myself instead of paying someone else do it for me so if anyone has any idea how to re sleeve a throttle shaft, enlighten me please. I was told a hand reamer would work...what's that?
Next, are there any updated "cures" for that base gasket? I read a post from a few years ago at JU and they were talking bout using sheet metal or aluminum to fab a new adapter. Dont really want to do that. What's the latest and greatest? Thanks for all the help so far.

'88 YJ
USMCYJ 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