Changed T-stat, Coolant, Hoses, Now its Misfiring???

[91LTDProject]

My radiator let go on my way to work last Wedsday, so I decided to do some work on the car. I had another rad that was about 5 months old from the 91, and a set of upper and lower hoses the same age. I also had a 170* thermostat that I got by accident through the shop instead of a 195*, so with the super hot weather we've been having I put it in. Well during the job, I ended up having to replace those little hoses that run off the water pump cause they looked ready to explode. I get everything back together and fired up, bleed the cooling system, set the timing back, and go for a drive. The car now has a low speed misfire, like say parking lot cruising speed, foot just tapping the gas. It also misfires when cruising down the road at about 40km/h with very little pressure on the gas pedal, and if you come to a stop and brakestall it, you can really feel it. Only thing I can think thats causing it was something to do with my moving of the distributor to get better access at the right t-stat housing bolt, but I marked it with chalk before I moved it, then re-timed it afterwards to 14*btdc (what I set it to last time I went to the track, ran great until now) to verify that my markings were accurate. Its kinda annoying me. And on the way to the mall tonight, the hood released a large white plume of smoke, another heater hose blew up. Had to nurse the car home and will have to get supplies from work tommorow to fix it. Guess the 19 year old rubber had enough.

[85crownHPP]

could be you just disturbed the wire connector for the TFI module and its got a bad connection.... wiggle it around with it running see what happens

[91LTDProject]

thing is that its not missing at idle, only under load with your foot in the gas a bit, whether it be hitting the brake and the gas at the same time, or just cruising at low speeds with the gas on just a bit.

[gadget73]

Sounds like moisture in the distributor cap or under the plug wires. Might want to pull them off and make sure everything is dry and all the connections are tight.

[91LTDProject]

That was the first thing I thought gadget. I had hosed down the engine bay cause everything was covered in coolant. Took off the cap and blew it out right afterwards, next day after I noticed the misfire on my drive home, i took off all the plug wires and blew them out. No such luck

[gadget73]

water in the tfi connector? water in the black and white connectors on the side of the intake? damage to the vacuum line for the evap canister? it runs down behind the ac bracket (well, used to), but its up front there somewhere.

[87mercman]

Turn down your timing, or run try 93 octane. IIRC 10-12* is stock timing, 12-14* is advanced, and running it advanced like that almost always REQUIRES 93 octane to keep from misfires and such.

[gadget73]

if its over advanced, it will just ping. If it ran that way before, that shouldn't be it.


Might want to just buy all new hoses. You're going to blow one after the other till you change them anyway. Its just irritating as hell to be stuck somewhere because a hose went kaboom.

[FordInPossession]

By the way, a 170 thermostat in a near stock car is not a soilution for it being hot outside. More than likely, that 170 stat will just stay open and not allow the coolant to cool in the radiator before ti goes back into the engine. Keep an eye on your gauge and if you see the temp climbing at idle, change back to a 195 and make sure your fan clutch is working properly. More often than not, that'll cool better than dropping the temp in the stat. Also check for water near the sparkplugs or trapped in the boots there. Make sure to used dielectric grease at the plugs and at the cap to make sure any water still there won't make a difference and so that new water won't get in

[91LTDProject]

I changed the other hose that blew yesterday and it seems to not be misfiring as much now. I turned the timing up to 14* last time I went to the track and put 94octane in then. AFterwards when I filled up with regular, I checked for pinging, and there was none to be found, so I've kept it at 14*. All my sparkplug boots are allready packed with dielectic grease, one of the first things I did. And my 90 and 91 both had a temperature gauge, this car has no gauge at all, not even a temperature idiot light. It has nothing to tell you the temperature of the motor. Something I have to take car of, but I'm still trying to figure out where I'm gonna start mounting gauges so that they dont look ghetto.

[Lincolnmania]

sounds like it needs a tune up!

[91LTDProject]

Did plugs, wires, ran a seafoam-like treatment through the engine, and put a new coil in about 3000km ago.

[OVERKILL]

A 170 is a bit low, a 180 T-stat is pretty much the "ideal" T-stat for an EEC-IV equipped vehicle because anything much above 190 degree, and the ECM starts pulling timing. Will you notice a performance gain? Probably not The low-temp "Chevy" T-stats like the 160 and the like, will prevent the engine from reaching ideal operating temperature and can contribute to sludge build-up, and the like. The temperature reaching 170+ degrees is also one of the items the ECM looks for with the ECT before switching from OL into CL........

[91LTDProject]

I see, looks like the old ones goin back in.

[OneBadLSE]

I had a 91 GM with a mystery misfire. Turned out to be the TPS shorted out. The car was acting all kinds of weird. No start condition, racing like crazy, hesitating like you wouldnt believe, etc. Disconnect the TPS, start up, and drive. Your miss should dissapear. It did so on my 91. Plug it back in, and you should get your miss under a load again.


Please let me know what happens! You may actually leave it disconnected as it will refere back to its default value. Oh, and you will smell a richness comming out of the exhaust. Dont fret. You gas milage WILL REMAIN THE SAME!

--Len