TJ with L98 Mechanical Issue -
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post #1 of 3 Old 04-30-2013, 11:15 PM Thread Starter
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Location: Edmonton
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TJ with L98 Mechanical Issue

I have a 1997 Jeep TJ with a 1990 Corvette L98 TBI motor in it. It is using the stock jeep in tank fuel pump unit (Fuel pressure regulator I think, can't remember). The L98 motor also has a fuel regulator under the plenum which I know is still operational

Recently it has developed a driving issue:
- Starts warm or cold like a dream
- Hesitates a little till warmed up
- Idles like a dream
- revs up while not in gear like a dream
- seams to run fine at 60 mph

Here is where it goes bad:
- under hard acceleration it bucks violently. Best way I can describe it is like some one is flickering a light switch off and on.
- This tends to be somewhat intermittent...but is happening more than it isn't

I have checked the minor things plugs, wires, and distributor. All good, have yet to check the coil...

Did a fuel pressure test off the Schrader Valve today with the pressure regulator and here is what if found:

- When key is turned on but not started, and cycled 3-4 times, the furl pressure only build to 10 PSI
- with the motor idling it sits at 35 PSI
- While performing a driving test the pressure fluxuates a little from WOT to no throttle. Of course while trying this test today it did not act up and buck.

I am going to continue to try road test in hopes that it will repeat the symptoms and then monitor the fuel pressure for drops or major fluxuation while driving condition exists.

Failing this I am 95% sure this is a fuel pump do to extremely low key on only fuel pressure build up. the pressure while idling and driving is still low from what spec is (L98 fuel regulator should have 40 - 42 PSI while running) so it is definitely 5 PSI low.

I believe the fuel pump is the problem, but question this without seeing what happens with the fuel pressure when driving condition happens.

Any input or thoughts would be greatly appreciated

Thanks for all you help to date...this site is my new evening entertainment.

Wanted opinions on something else with the fuel system...
I believe the stock TJ fuel regu;atur is still in place, and there is also the stock fuel While the GM Allows 41 PSI..
What do you guys think about leaving it this way, or should I remove the stock TJ one?

Last edited by 95harley; 05-01-2013 at 07:09 AM.
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post #2 of 3 Old 05-01-2013, 06:33 PM Thread Starter
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Location: Edmonton
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Of course when your trying to trouble shoot something it won't replicate the problem. Drove it 100 miles today and it worked flawlessly...
key on test 40 PSI every time
Idle with vacuum attached to the regulator test 35 PSI (would like to se 40-42 PSI).
expected fluxuation depending on throttle under load.

So now that I have returned my buddies fuel pressure gauge it'll probably start acting up

A really good friend who is a pretty good Mechanic thinks that sitting for the last 8 months, and probably bad fuel are the culprit.
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post #3 of 3 Old 05-05-2013, 05:14 PM
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2003 TJ Wrangler 
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Location: Skamokawa
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Usually quick jerking type misses are ignition related. Slow hesitation type problems are either fuel or exhaust. What you describe sounds to me like a secondary ignition problem. This will show up worse under high load low rpm situations and may go away if you gear down. This will be coil, cap, rotor, wires, plugs.
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