TBI 454...Pedal floored, wont rev past about 2500? (video)

[Biggershaft96]

Keep in mind we like pics

 

[454/4X4]

Well, ben about a year...still doing it. I bought a K3500 CCLB dually and been enjoying it and the other 2 trucks without a single problem...came back to this truck, and its still doing the same crap as before.

Ive decided that, it isnt fuel related, in the sense of demand, or supply...as I can go out on the road, hold it in 2nd gear..and go to 80% throttle and it will hit 2nd at 4000...and pull through 2nd to the redline...never miss a beat, smooth as silk. If I go out and floor it..it stumbles, sputters, misfires...gets up to about 30mph...tops out.

I dont think its spark, in the sense, same as above...its all new, and it all pulls hard to the redline...

It seems like, its something in the computer, telling it, at WOT....cut spark...It literally acts like a modern engine does with a rev limiter...

I made a new video, from the rear view.

First rev is about 75% throttle to 4500 revs....2nd rev is matted....hear the rapid on/off/on/off....but no smoking when it does this.

http://vid97.photobucket.com/albums/l232/RED-85-Z51/Mobile Uploads/20150110_135924_zps11pbefle.mp4

 

[SkyHighColorado]

If it were my truck I would start looking into the computer and sensors because to me it sound like its being limited electronically.

its a 95 correct? It would help a lot if you got an obd usb cable and hooked a laptop up to the truck with tuner pro so you can monitor everything going on. It would make life easy.

 

[454/4X4]

If it were my truck I would start looking into the computer and sensors because to me it sound like its being limited electronically.

its a 95 correct? It would help a lot if you got an obd usb cable and hooked a laptop up to the truck with tuner pro so you can monitor everything going on. It would make life easy.

I have a spare idientical ECM that has proven to work perfectly on another truck, it made no difference. The eprom is an updated reflash of the original BIN file, the original eprom was faulted and would not allow it to idle down, I suspect someone had tried to custom tune it and messed it all up. I never tried to take it WOT with the original eprom...so I cant comment.

Im thinking of trying a hypertech street runner, as it says it remaps the WOT inputs ONLY...so if my eprom WOT setup is bad, the chip should fix that..maybe?

I have no laptop and absolutely no skill when it comes to tuning or working those kinds of programs.

 

[PNDSND]

I know this is an old thread but I have tried almost everything. My 1994 dually is doing the same thing. I can watch the injectors shut off and on while it is doing this. It will also do this at a steady throttle around 2000rpm's. I'm at a loss. Just curious if OP ever resolved this issue.

 

[Schurkey]

I know this is an old thread but I have tried almost everything. My 1994 dually is doing the same thing. I can watch the injectors shut off and on while it is doing this. It will also do this at a steady throttle around 2000rpm's. I'm at a loss. Just curious if OP ever resolved this issue.

What is your fuel pressure when it's misfiring?

Connect a scan tool, watch the data stream. Verify all sensors and computer outputs. Verify EGR operation. Assure that the spark advance works properly.

How old are the usual "Tune-Up" parts--cap, rotor, plug wires, plugs, pcv valve, fuel filter, air filter?

 

[PNDSND]

The usual tune up parts you listed are new. I went back and swapped them back out with the old ones and some extra new ones that I have just to see if there was a change. Also have done new distributor, coil, ignition module, temp sensor.

I am going today to grab the adapter to test fuel pressure. If it is in park and I mat the throttle it will set there and act like there is a rev limiter at about 2500 rpm it also backfires through the TB when it is doing this. I can see that the injectors are shutting off and on repeatedly. If I am in drive and mat the throttle it takes off and doesn't miss a beat. I can also see the injectors shut of when I hold the rpm's at around 2000. It will also have this miss driving down the road. I have verified that the injectors are losing signal when they cut out.

My next steps are to check fuel pressure and go back through the TBI with another rebuild kit. Just to make sure I didn't do something to cause this.

The truck is a 1994 c3500 7.4l. It has around 145000 miles. The previous owner was using it to tow a large boat and was sitting around when it wasn't pulling the boat.

I started chasing electrical items because the Tach jumps up when it does the miss at 2000 rpm. I have swapped all the internal parts of the distributor with other parts incase it came with bad internals.

 

[Dropped88]

When you say swapped internals in the distributor did you just swap the module. Ive seen plenty of the new china distributors have pick up and the magnetic wheel have issues.

My 92 454 had a new JUNK auto zone dizzy installed by PO and never ran right and had a miss around 2k. Took a rough oem dizzy freed it up and fixed my odd running issues.

As for losing injector pulse that signal comes straight from the dizzy so if signal wire and ecm is fine. Then pulse lost has to be with dizzy. Atleast thats how its been in my experience with many tbi trucks

 

[Schurkey]

Distributor, or wire harness between distributor and ECM.

I would want a scan tool to verify cam signal (RPM signal) to the ECM.

 

[PNDSND]

I appreciate the feedback, I believe I have found the problem. I swapped the shaft of the new dizzy with the old one. It changed the miss to a different RPM, not sure what was going on with that but whatever, it told me I was on the right track. I then swapped out the brand new coil with the old one and that seemed to change everything. The new coil is a Delphi. The old one is original to the truck. As of right now the truck is running great.

BTW, I had checked the Delphi coil with a multimeter when this problem started and everything was within spec. I know this doesn't tell me anything about how it is acting when it's functioning, I was just ruling out overall failure of the coil.

Lesson learned: don't change a bunch of stuff at one time. I thought I was doing right with the parts that I had bought but I guess you never know.

Thanks again