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'97 12v Won't Go Over 45mph

Mad Maxx

Mad Maxx

See, what had happened was...
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I Picked up my Truck from the Dealer just before.

When I Left, it was Driving Perfect...then the Shit Hit the Fan.

The Truck won't go over 45mph, and the RPM's stay at about 2k-2.2k and no matter how Far I Push the Gas Pedal, nothing Changes. The Truck doesn't Speed Up, Kick Down, Bog, nothing. It just Stays at 45mph. But then just the Slightest Incline in the Road, and the Truck doesn't have enough Power to Pull itself up it, and I Lose Speed FAST.

Also, when this happens, if I don't Slow Down Slowly, like if I just Get Off the Gas and get on the Brakes, the Truck will Stall Out and Shut Off.

The First time it happened, after it Stalled, it had some Trouble Starting back Up. Once I Finally got it Started, it Ran Fine, got it up to 60mph no Problem, Shifted fine, then all the sudden, it Slowly Slowed itself back Down, and wouldn't got over 45mph.

It's back at the Dealer now, and they said they'll get it Fixed ASAP.

Anyone have any Ideas what it could be?
 
Do you think it could be something as simple / stupid as that the dealer didn't prime / bleed the system when they changed the fuel filter?

Would that cause these Symptoms?

It didn't Buck or Chug like there was air in the Fuel though.
 
Well that doesn't exactly give you a nice warm fuzzy feeling about your new work truck...
Hope it's something simple. Not priming the filter isn't likely it though. That would probably have cleared up pretty quick by itself.
 
Well, it's hard to speculate since they have the truck and are supposed to be fixing it but I would say the LP. IIRC it's a Mech one on the 12v. Atleast the older ones I am pretty sure were. That is a good engine. Don't forget to address the KDP.
 
Governor springs in the pump.

The stock springs start pulling fuel back right in that range and by the time you hit 60 MPH, the truck only makes about 60 HP.

Swap the gov springs for a 3K set, or 4K if you upgrade the valve springs and it's a whole different animal.

Also, check the fuel pressure going to the pump. The P pump like a lot higher pressure than the VP44's or CP3's. 45 psi and you have a happy pump and make good power.
 
Cumminalong said:
Governor springs in the pump.

The stock springs start pulling fuel back right in that range and by the time you hit 60 MPH, the truck only makes about 60 HP.

Swap the gov springs for a 3K set, or 4K if you upgrade the valve springs and it's a whole different animal.

Also, check the fuel pressure going to the pump. The P pump like a lot higher pressure than the VP44's or CP3's. 45 psi and you have a happy pump and make good power.
Click to expand...

When I could get it up to 60mph, that's when it was Driving Fine, when it was having the Problems, it would Top Out at 45mph.
 
Could this also be a Tranny Issue....ALREADY?

Something Stuck or Clogged in it, not letting it Shift, thus keeping it right where the Motor Defuels?
 
Doesn't sound like a trans issue. If you have your foot buried and there's no power, the trans isn't going to upshift, it thinks the motor is loaded down.

It sounds like a fuel issue.

First thing I would check is the fuel pressure to the pump and change the fuel filter.

If you have good pressure to the pump, the next thing I would do is change the governor springs. Just swapping the gov springs makes a HUGE difference in the 12V's performance.

Once it can actually fuel all the way through the RPM range, it picks right up.
 
Didn't Hear from the Dealer Today, so hopefully that Means they Found something and are Waiting on Parts.

I'm gonna give them a Call Tomorrow and See what's up.
 
Definately check the fuel pressure. I know that I have heard of the older 96 and back style fuel heaters plugging up and causing them to starve out and fall on there face. Sounds to me like your runnign out of uel which is turn not giving you enough boost to allow the aneroid to let the RPMS go up anymore. And yes they use a mechanical fuel pump on the drivers side rear of the block. And the infamous rubber fuel lines on the 96- trucks can cause alot of issues as well. Replace them with marine grade EFI fuel line and don't worry about em again.

Also this may sound stupid, but I have seen problems with the fuel shutoff solonoid not pulling the shutoff all the way up and limiting the power to only about 2K RPMS.
 
I just went throught the same problem it wasn't my fuel filter that was cloggged it was the fuel water seprater. there is a screen in there that clogged solid. cleaned it out and the truck runs like new again
 
Well, Big Surprise here, the Dealer just Called and said they Spent all Yesterday Looking at the Truck, with 3 different Mechanics on it, and they didn't Find anything Wrong with it.

I told them to Check the Overflow Valve and gave them the Pressure Range that it should be in.
 
Just Heard back from the Dealer, and they said they got it to have the 45mph problem.

So now they are Looking into it In Depth.

I'm glad it happened for them now, so they don't think I'm Crazy.
 
Acesneights1 said:
is that what they run ?? 45 PSI ? Also Rich does that gen of 12v use a mech or electric LP ?. I know my 8.3 has a mech LP.
Click to expand...

The 12V has a mechanical lift pump.

And yes, 45 psi is ideal on the P-pump.

The VP44 and CP3 likes to be between 10 - 20 psi, with 13 - 17 bing ideal.
 
john65td said:
I just went throught the same problem it wasn't my fuel filter that was cloggged it was the fuel water seprater. there is a screen in there that clogged solid. cleaned it out and the truck runs like new again
Click to expand...

That's actually not a water separator, it's just a pre-screen to keep trash out of the lift pump.

And yes, that can get funked up.
 
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