Bucking when driving
Thread Starter
Le Mans Master
Joined: Jan 2004
Posts: 8,295
Likes: 30
From: one night in Bangkok you are never lonely
Bucking when driving
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
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
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,218
Likes: 1,174
From: Southlake, TX
But, My hunch is that you have a FPR issue as it wont hold pressure.
Thread Starter
Le Mans Master
Joined: Jan 2004
Posts: 8,295
Likes: 30
From: one night in Bangkok you are never lonely
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.
But, My hunch is that you have a FPR issue as it wont hold pressure.
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,218
Likes: 1,174
From: Southlake, TX
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.
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.
Melting Slicks
Joined: Jan 2008
Posts: 2,054
Likes: 120
From: AZ
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.
Can you post a vid of the FPR jumping about? That's quite the variation! No aroma of gasoline, I guess.
Supporting Vendor
Joined: Oct 2004
Posts: 761
Likes: 68
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
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
Thread Starter
Le Mans Master
Joined: Jan 2004
Posts: 8,295
Likes: 30
From: one night in Bangkok you are never lonely
I don't have an MSB box just the stock dizzy.I will try sending the video to you now.
Melting Slicks
Joined: Jan 2008
Posts: 2,054
Likes: 120
From: AZ
It's probably fuel related and Bill gave a good checklist to find it.
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Thread Starter
Le Mans Master
Joined: Jan 2004
Posts: 8,295
Likes: 30
From: one night in Bangkok you are never lonely
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.
Last edited by Bangkok Dean; Sep 1, 2017 at 01:54 AM.