Wierd Problem...

[99V8SHO]

For some reason my car does not want to go over 100mph. I got a little spirited today on my 350 mile drive from Fayetteville, NC back here to MD. I was going about 75, punched it, it dropped into 3rd and pulled hard all the way up until 100mph at which point it just stopped pulling. It was like I hit a brick wall. It started bucking and refused to go over 100. I let off a bit, let it drop into 4th, then tried pulling past 100. No luck. Just sat there bucking. I am stumped. The only thing that I can think of is there is something wrong with my ECU. My speedometer reads dead on, so I am pretty sure the VSS is ok.
Tomorrow I am going to have it scanned for codes and see if that turns up anything interesting.
Any ideas??

 

[SHOZ123]

Fuel Filter?

 

[99V8SHO]

I am just shy of 60K miles, so it is time to replace that anyways. But why would that keep me from going over 100mph? Lack of fuel pressure? I would think that would take effect well before 100mph.

 

[Steve Dionne]

Just thinking out loud Roman, but how clean is you air cleaner and MAF. It may be that when you get to that speed you're not getting enough air. I know from experience that cone filters left exposed in the engine bay get very dirty very quickly. I'm going back to the panel filter next weekend. Just a thought.

 

[SHOZ123]

The fuel filter would be a restriction at high speeds. When going 100 mph you are using much more fuel per minute than at any speed less. Where as at lower speeds the engine might be at higher speeds it does not stay there for the long term.

If it was the MAF you would be setting a code, if it was the air filter it would show up at the lower vehicle speeds but higher engine speeds.

 

[Shakey]

Just for the discussion here...

I replaced my fuel filter lately and experienced a noticeable increase in performance. It's not too difficult to do and it may help, if not correct the problem. It's worth a shot.

 

[99V8SHO]

Today I went and bought a new fuel filter, I will be putting that in tomorrow with my 24mm fsb. I had it scanned for codes today, nothing to write home about. Steve, about a month or so ago, I reverted back to the paper panel filter and a new MAF as my old one went bad. I think for now I will leave the cone out. I know for a fact the filter and MAF are clean.
Speaking of the ECU...I had my mechanic strap a scanner to it that reads everything the computer does. Everything looks ok, except for the injector pulse width and timing advance at higher RPMs. He told me that at higher RPMs instead of richening out the A/F and advancing the timing, they just stay the same. He said it is a coding problem inside the computer. He also informed me that a TSB was put out for all SHOs built after 04/99. The computers needed reflashing. Mine was never done. He recommended that instead of having it reflashed (may hinder performance) to just go get a chip. (When I say "he" I am refering to Kevin Mahoney at Protech if anybody here knows him).
Any suggestions?

 

[99V8SHO]

Well, I changed out the fuel filter, problem is still there. I guess I will look at the fuel pressure regulator and fuel pump next. Something just is not adding up here.

 

[Ian Macoomb]

Well, I changed out the fuel filter, problem is still there. I guess I will look at the fuel pressure regulator and fuel pump next. Something just is not adding up here.

Have you ever felt a miss at idle? My car lacks midrange power when a coil is going bad. Try putting it in 2nd and flooring it from a stop. It will bog pretty bad but it should run okay. When I've got a bad coil it will totally run like **** when bogging it like that.

 

[99V8SHO]

I don't think any coils are going bad, my idle feels fine. Unfortunately I have one of the 99.5 SHOs, so I don't have the option of starting in 2nd. I am pretty sure all the spark plugs are good, as they were all replaced when my cams were welded 12K ago.

 

[ricky]

Just a thought, but isn't 100mph about 34/3500 rpm in top gear or about the speed the IMRC kicks in?

 

[99V8SHO]

In top gear, yes. But this also happens in third gear, and that is right about 5K-ish.
I know that the IMRC is working fine. I can definately hear (and feel) the secondaries kick in at 3400.