Topic: 86 TBI coolant bypass tryout

[TURBOD16V]

hi guys new here.
 in my search for more power on my 86 2.5 XJ TBI 5spd. i figured i could bypass the coolant flowing thru the manifold and free up some hp with a colder manifold.
 so i went to lowes got a 1/2" T fitting with a 3/8 port in the middle. 2x3/4"barbed 1/2" pipe thread adapters.
 removed coolant temp sensor from manifold and instaled it in T. cut and moved hoses from the manifold to a straight shot from t stat housing to heater thing with the coolant temp T pluged in the middle.
 ok did not turn it into a power house but it cruises way better on the highway! going up hills, i travel everyday to work, without downshifting from 5th -4th now!  :shock:
 great right...wrong
 for some reason now it sometimes stumbles at low RPM, always lacks power at low RPM and ocasionaly dies when droping to idle.
 but it runs so great above low RPM!!!  :evil: (how low i don't know, no tach! but maybe under 1500rpm,a good blip of the throtle will get it going)
 any ideas how to get it running better all the time?
 does coolant run around the EGR on this? an maybe the EGR is causing the problem? tried unpluging the vacuum but no dif.
 gonna try resetting the ECU today while at work.

 also should i try increasing plug gap as i have a hotter coil but stock gap.
any other sugestions?
 thanks guys. :D

[chardrc]

hmm i never thowt of doing that.. if we can fix your lowend power ishue i might just have to do this myself..

[TURBOD16V]

Well i went to move my jeep and it was fine no stumble or bog or stall'n.
 but it is a lot warmer out in the evening than it was early this morning when it was realy acting up.
 just disconected the battery 10 minutes ago see what hapens after it sits abit.
gonna increase plug gap this weekend and also see how that works.

[TURBOD16V]

UPDATE
well i put it all back to stock. I miss the top end power.
 i tried regaping plugs,reseting ecu and it still stumbled on the low end.
perhaps the TBI computer just cannot compensate or adjust enough.
 i use this trick on other vehicles and it always works but none of them had TBI.
 on a plus side between playing with the plugs i found it does run better with them gaped at 45 with the hotter coil.
next i plan on having my freind make me a 1" TB spacer outta high temp plastic. see how that works!  :?

[YJmechanic]

drastically changing the temperature to the manifold can make the sensors change how they apply the fuel and timing.  with the heat taken away your motor thinks it is not getting hot and is sending improper signals.  you caould probably have your ecu flashes for a higher altitude and your setup may work.  cool idea by the way never thought of that.  but then again i'm multiport

[chardrc]

my dad said they put the collent thow it to warm up the fuel so it burns beter which i why it would work for mpi but not tb1

[TURBOD16V]

I figure that the old 86 TBI ecu just can't adjust enough for the drastic change in temps.
 also i saw that the MPI 2.5's temp sender is in the t-stat housing and that there is no coolant flowing thru the manifold.
lucky MPI's

[Jeffy]

I wonder if you'd be able to swap to a later thermostat housing then run the sensor there...  It would trick the PCM.  The other option would be to later the signal from the original temp sensor which would require some research.

[TURBOD16V]

I thought of switching T stat flanges, but puting the sensor in the bypass hose with a T made it easier to put back to stock.

[YJmechanic]

jeffy's got a good point in theory at least that should work and it shouldn't cost much a junk yard for the housing.