Stumble at 105 mph

[SacDoug]

I was driving the truck last night. I have not tried to go over 100 yet with it so I decided to floor it and give it a try. I got up to 105 and then it stumbled. It was as if the engine cut off for 1/2 second then continued. I tried a 2nd run at it and it did it again twice. I could not go past 105.

Everything is stock with a few exceptions:

MSD super conductor plug wires with less than 5k miles on them.
NGK Iridium IX plugs gapped at .035"
New K&N air filter
Re-routed IC hoses
Added a tranny cooler and filter
Ported Turbo exhaust side

The cap and rotor are brand new. The ignition is set dead on at 0*.

Any suggestions as to the cause or what to look for would be greatly appreciated.


Thank you.

 

[dgoodhue]

Re: Stumble at 105 mph

Is the engine going into OD around 100mph? You might be hitting the rev limiter in 3rd gear.

 

[attackdog]

Re: Stumble at 105 mph

Yep. Sure sounds like the rev limiter to me...
-Deano

 

[wantingasy]

Re: Stumble at 105 mph

Cutting off for a 1/2 a second then it goes again sounds like it's overboosting. Does the check engine light come on for like 10 seconds after that then turn off?

 

[SacDoug]

Re: Stumble at 105 mph

Is the engine going into OD around 100mph? You might be hitting the rev limiter in 3rd gear.

I didn't even think of that. I forget that it is only a 4 speed. The truck is still in 3rd. Should it have shifted or do I have to get off the throttle for it to shift into OD?

 

[wantingasy]

Re: Stumble at 105 mph

Do you have it in OD when you're getting on it or D. If in D, manually shift it into OD at about 4300 rpms? Someone correct me if I'm wrong.

 

[dgoodhue]

Re: Stumble at 105 mph

I didn't even think of that. I forget that it is only a 4 speed. The truck is still in 3rd. Should it have shifted or do I have to get off the throttle for it to shift into OD?

If you shift it, a syty tranmission should goto into OD.

 

[SacDoug]

Re: Stumble at 105 mph

I have it in the D next to neutral which I assume is the OD "D". So if I want to go into OD while staying open throttle then I need to manually shift it such as 1-2-D-D?

 

[GM TURBO]

Re: Stumble at 105 mph

If it is a stock trans - it will upshift at WOT. If it has been rebuilt there is potential it won't and you'll have to lift your foot to get it to upshift.

 

[TYTILIDIE]

Re: Stumble at 105 mph

If its not your trans it may be that youre leaning out. My truck used to do that at that speed. If its your trans, Im sorry. Try it in OD

 

[Black Knight]

Re: Stumble at 105 mph

If its not your trans it may be that youre leaning out. My truck used to do that at that speed. If its your trans, Im sorry. Try it in OD

Mine was the same, at high WOT runs in 4th it would cut out, put in the Walbro and haven't had a problem since.

 

[SacDoug]

Re: Stumble at 105 mph

It was in OD when this happened and the tranny never upshifted to 4th. As far as I know it is the stock tranny. I have only owned the truck since May.

Does this mean that there is something wrong with my tranny since it did not upshift or might there be another cause?

 

[Big Mike]

Re: Stumble at 105 mph

What chip is in the truck? Stock chips were speed limited. Mine is an early SY and would not go over 100 mph.

 

[SacDoug]

Re: Stumble at 105 mph

What chip is in the truck? Stock chips were speed limited. Mine is an early SY and would not go over 100 mph.

I have the stock chip. Mine is #1004. Does that mean that I have the same top speed limit as you? I thought all SyTy's had a top speed limit around 125 or so.

 

[Quickstop [UK]]

Re: Stumble at 105 mph

speed limit was to about that - 125 or so. Mine is doing the same thing. I DM'd the run if anyone had some time to look over it.

No CEL / SES came on, but the exhaust sounded like it backfired. Did you get that?

Walbro going in as soon as the fuel hanger gets here.

 

[Big Mike]

Re: Stumble at 105 mph

It was long ago but I have since then changed the chip to an Ultimate, problem solved.

 

[dgoodhue]

Re: Stumble at 105 mph

I have it in the D next to neutral which I assume is the OD "D". So if I want to go into OD while staying open throttle then I need to manually shift it such as 1-2-D-D?

I have found that with some stock SyTy tranny's, I have to do the D to OD shift myself. I never use 1&2, I let the tranny shift itself.