5.0 Engine Max Rpm ?

[lowflyingbird]

I've asked this before, since then I've done some work on my truck. I have a 98 5.0 and it cant break 4800rpm. If I floor it it makes it to 4500-4800 and shifts no problem, but other 5.0 Explorers I've driven even in stock form seem to rev out much higher. One friends EX passes the 6000 on his tach, it may have been chipped/reprogrammed? we dont know. He was not the orig owner.
With my truck parked, and I floor it goes to the same 4800 and seems to weakly hit a rev limiter. I've had other Fords that had limiters I hit normally hard, but easily.

On my truck I had the bad and cracked stainless exhaust manifolds. They are gone, as well as the rear cats. I now have the cast manifolds which look like they flow much better, and a 2 1/2 Dynomax superturbo exhaust.

Does anyone have any ideas why this truck wont rev up? I have several thoughts; First, the computer sucks!!? Second, possibly clogged upper cats? Third, suggestion by a friend that the torque converter is crap?

PLEASE HELP :thumbdwn:

 

[Dan Whitaker]

It's not the torque converter as it would not be spining with it in park.

 

[Turdle]

I think the v-8 rev limiter is 5300 rpm's at least mine is-

 

[CougarX]

Maybe your tach is just off?

 

[tktrain]

I think the v-8 rev limiter is 5300 rpm's at least mine is-

Jon: I hit about 5500-5600 on floor-boarded in-drive 1-2 shifts (realizing, of course, that the factory tachs are not very accurate). I do agree that the TC would have nothing at all to do with it.

I would be looking at the primary cats, the ignition system, and the cam/springs. The stock valve train could easily start to float out at around 4800 RPM. The OEM springs are very light in these motors. Also remember that the stock cam is smaller than the old HO cam. Only about a .421 lift versus .444 for the HO.

 

[Turdle]

Keep in mind (before calling me crazy) my engine is built for 7000+ rpm's

I can hold foot to floorboard in park-or neutral, rev limiter kicks in, and highest reading on scantool (displayed on laptop) is 5260 rpm's. My tach does read aprox 5500 though, when this occurs.

The torque converter is spinning BTW--it is attached to the flexplate---

The pump also pumps in park and neutral in our transmissions.

 

[IAmTodd]

My limiter kicks in at 5200. Normal shifts are from the high 4ks to 5k.

 

[lowflyingbird]

Hi,
I could believe its cats. But, valvetrain float is a strong possibility too. This engine has 165K on it, runs otherwise good. Tach I believe is about right, I've had other 5.0's and I know very well what 6500 is like, not like I would expect it from this truck.
I had a thought on ignition, but I doubt it unless the computer is doing it. Another thought was fuel delivery????? It has the origional pump in it and might be weak???? Just a thought?

 

[IAmTodd]

Pull the battery for a while to let the ECM reset. May not be a bad idea to try the fuel filter. Its located on the frame rail under the drivers door. Pick up the tools to remove it as well.

 

[lowflyingbird]

Hi,
I cleared the ecm a bunch of times, and have changed filters. Its probably due for another though anyway. I'm leaning more and more toward the valve springs. When I floor it parked, before hitting what I think is the rev limiter, it does sound like its starting to break up . And when driving and flooring it, the power does fall off at high rpm. just before shifting.