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I'm thinking the TPI ECM needs the reference pulse from the distributor ignition module to get the spark going. I'm thinking the TPI ECM also needs the reference pulse from the ignition module to enable the fuel pump relay for more than a few seconds. dave w

The vacuum advance distributors are a 4 pin module and the TBI is a 7 pin IIRC and the ECM needs a reference signal for spark and also for the fuel pump. Also remember that the vacuum advance distributors have a mechanical advance system as well and you need a distributor with NO advance mechanism at all since the ECM controls it.

Thursday Update; using road test after,,,above The problem was stiil threre, I went to mufler shop,had the Even side Cat replaced, Then went for road test ,,after "battery diconect" "clearing', 1 hour freeway driving,,fine 2 hrs or town driving,,fine 3rd hour later on rural road,, it started bogging again,, at only half throttle,,? I returned to Muffler shop and instaled; the odd side cat which was realy hot,,...

suggestion- cummins first, then gear swap, you might be surprised! i had an '03 f350 with 3.73's a 6 speed and 35's that didwell with the powerstroke.

if i remember right theres a brown wire that sticks out off the main wiring harness on firewall helper side. and you unplug it to time.will check today at work if i,m correct! if i get it right the tv cable adjust line pressure for a firmer shift when you step on the gas hard,this is why when not ajusted right transmission may slip on w o t !

I've got a 90 CC with 8" lift & 37's with 3.73 gears. At best I get 12mpg. After a gear swap I'm definately going with a cummins.

Ohh, you just used the Holley throttle body itself. Okay. The fuel pump relay is fed a low current 12 volt sorce by the fuse panel with it's own fuse for fuel pump. The ecm grounds the control side of the relay (low current switching side). When the ecm grounds the circuit, the relay "turns on" allowing B+ to go to the pump and turns on. Of course the fuel pump is grounded external of the relay. Ecm using grounding...

I never tested the TPI module, just the one in the dizzy with vacuum advance. I'll just swap the distributor out since I have one and see, if that doesn't work I'll get a new computer. Can I ask why I can't use the vacuum advance distributor? It should still have spark, unless the TPI ecm doesn't read the old 3 pin module since TPI with a big hei distributor has a 5 pin module...

Quote: Originally Posted by 4X4HIGH Anyone that claims to get 18-20 from a gasser burb has bumped their head. It isn't going to happen in this lifetime. I know it's hard to believe but my old man back in the late 80s early 90s drove a 87-89 2wd 1500 suburban and always got 18 on the hwy. Back then the speed limit was 55 though. He does get better milage than other people in the same vehicle, could be in his head or maybe it's...

My mom had an 89 burb with a 305 in it. On the highway we always got a steady 18mpg. But that was also in Oregon with a 55mph limit.