Just picked up a 87 454 4dr dualie, upon purchase, truck idles about 2500 rpm and had horrible part throttle manners.
Found throttlebody gaskets to be bad - both of them real bad.

After fixing, idle came way down to normal ranges, but still dies when in gear and part throttle is still bad..
Removed IAC and cleaned and seems to work fine, and can hear on initial startup..

Also manifolds are real real hot, like 700 surface temp and smells rich - checked after noticing extreme heat under hood.

Since this problem I have changed plugs, wires,cap,rotor, Removed cat and made free flowing 3" exhaust (Fur fun, Checked EGR - moves just fine, Scanned to check BLM, IAC,TPS,Park/Neutral switch.. Checked timing.. and changed O2.

Everything seems ok, no trouble codes present...

Did find that after removing ESC wire truck idles in and out of gear just fine until you restart then starts missing and stalling... Im guessing it idles because its in limp home mode when wire disconnected.
Tried timing about 20* each way just to make sure, no change for better.


Any thoughts?

Truck runs great WOT, horrible part throttle.

 

replace the injectors

 

That's a TBI right? Hook up your timing light and point it at the spray comming out of the injectors. You should see a nice even spray (to check the injectors).

High temp on the exhaust usually means not enough timing, which causes the combustion to continue into the exhaust cycle. If you put your timing light on it at higher rpms does the timing look right?

 

Well thats the first thing I thought - and it just so happened that the base was set about 6 degrees retarded, so I bumped it up and though for sure that was problem!! Nope, still runs the same, Stronger but the same.

Injector spray seems uniform from what I can tell, even spray and trickles down walls of throttlebody. But also seems to spray alot to me.
Driver side has a slight flicker every once in a while but does not seem related to truck dying in gear..

Also I think if it was injectors that it would not idle great with esc disconnected like it does.. I also though that maybe the balancer moved on the elastic ring, so I hooked up esc wire and moved timing down to where base is set at 5* and it just got worse which tells me its something other than timing. And it runs good because its forced into limp home mode with esc disconnected and ignores all sensors.
Ill pull the map off my car today and try it, but looking at that one on scan tool it seems fine and linear.

Thanks for input guys, in appreciated.

 

Have you checked the bin (program)? It sounds like you have checked all the hardware thoroughly. If your sure all the hardware is good then I'd go after the ecm. Good luck

 

Sounds like an EGR problem.

 

Well thats next,
May try new ecm or prom - just seems weird there is no check engine and ecm scans ok.. usually if they are bad there will be no link..

Want to send ecm to craig moates to kave him solder adapter in so I can burn proms for and figure I can fix, but would rather find actual problem first..



Sqxbox:
EGR deffinetly makes sense, but I removed it and gasket was fine, its sealed when closed and opens easily... also put to vacuum and it opened..

I may try blocking off and see what happens.