Bangkok Dean

Hi, My L98 motor all of a sudden has started bucking or pausing when driving. It idles OK cold or hot 183*. I set the TPS to .54 volts using two paper clips + to the center wire and the – to the top wire.

The fuel pressure with key on is 30lbs and after 30 minutes key off it drops to 16lbs.

When running the fuel gauge bounces all over the place 10 to 50 very fast.

The Trans is a 700R4 I drive in drive and overdrive with the same surging.

Please let me know what you all think the problem is, thanks

billschroeder5842

My quick guess is that you have a fuel pressure issue. There are four major components that you need to check 1) Fuel Pump, 2) Fuel Filter, 3) Fuel Pressure regulator or a leaky injector. And I'd do it in that order.

But, My hunch is that you have a FPR issue as it wont hold pressure.

Bangkok Dean

How long after shutting off the motor should it hold fuel pressure?

billschroeder5842

Theoretically, indefinitely, but on these old cars I'm a little forgiving.

When ever I start my LT5 or the L98, I turn the key, pause for 2 seconds and then spin the engine. In the morning both spin/start in 2-3 seconds. After running and sitting for an hour both pop off in 1/2 turn.

whalepirot

Had that issue with the initial tune on my engine. More timing cured it, so I wonder if your MSB box is failing.

Can you post a vid of the FPR jumping about? That's quite the variation! No aroma of gasoline, I guess.

BlowerWorks

Bouncing at idle = issue !!!

Bangkok Dean

I tried posting the video but it won't take. There is no gas fumes.
I don't have an MSB box just the stock dizzy.I will try sending the video to you now.

whalepirot

I don't 'do' f***book and couldn't view the vid, as I PM'd.

I know the reputation of failures with MSD boxes, and saw the Blaster in the pic.

It's probably fuel related and Bill gave a good checklist to find it.

Bangkok Dean

Yes fuel pressure gauge bounces when idling so fast you can't see the needle.

Bangkok Dean

Fixed, changes the in tank fuel pump and the fuel filter, now 43 lbs fuel pressure. runs like it should.

hcbph

Glad it's fixed and thanks for getting back with the root cause. So many times things may be fixed but resolution never reported so can't help the next person with that issue.

VikingTrad3r

thnx for reporting back!

do you mean the pump and sock assembly or do you mean pump and on-frame rail filter? thnx.

Bangkok Dean

I have an intank fuel pump and an inline filter before the fuel rails. The only problem now is when at running temps it is difficult to start. I have to try several times to finally get it to start.

Bangkok Dean

Japanese in tank fuel pump.