I installed one of GRONK's TFI ignition upgrades a few months ago. The car was running and starting great up to a couple weeks ago (I maybe drive it once a week). Today I pulled the wires one at a time while it was idling, and found # 5 & 6 make no difference in how it runs. If I pull any of the other wires, it stumbles so bad it almost dies. I pulled the plugs on 5 & 6 (properly gaped NEW plugs that came with the kit), and checked the compression. Both had 150 lbs. I switched the 2 wires with others, and no change. I put a spark plug on one of the wires while it was running, and it has spark. I can only assume that the problem is ignition related because the fuel/air mixture can't decide not to go in those two cyls, and 150 # compression means that the valves are good. I can't imagine the coil being bad either, because it can't choose when to fire and not (the same every revolution of the dist). What would cause this? Anyone know what I can try?
So the wires from 5 and 6 are sparking correct? If so, that sounds very strange, and IIRC somebody else once had the same problem, and I believe they said when they replaced the timing chain and the symptoms went away.
Since #5 & #6 draw from the same intake runner, you might check to see if the intake gasket has failed and allows a vacuum leak.
Quote from: txjeeptx on January 31, 2012, 09:28:52 PM
Since #5 & #6 draw from the same intake runner, you might check to see if the intake gasket has failed and allows a vacuum leak.
Dude!! You might be on to something there! I will check that tomorrow. However, I did notice the smell of fuel when I was checking the compression. On second thought, it does miss a little at speed, so maybe that may rule out the intake gasket? Even though it is getting spark through the wire, could I have gotten 2 bad spark plugs out of the box?
There are a couple of big vacuum ports over the 5-6 runner running accessories. Plug those and see if it makes a difference. I think 5-6 run cooler too, last time I changed plugs those two were fowled, I was surprised that 6 ran at all, the gap was bridged with ash.
Quote from: BenM on January 31, 2012, 11:15:48 PM
There are a couple of big vacuum ports over the 5-6 runner running accessories. Plug those and see if it makes a difference.
Dude! you are the bomb!! (whatever that means). That was exactly the problem. There was a large vacuum line that was off the fitting just above the 5&6 intake runner. I am usually not stumped by something that simple, but this time I was. Thanks to all in this community (the 'Nest) that help make it the best automobile related forum on the WWW.
Quote from: BenM on January 31, 2012, 11:15:48 PM
There are a couple of big vacuum ports over the 5-6 runner running accessories. Plug those and see if it makes a difference. I think 5-6 run cooler too, last time I changed plugs those two were fowled, I was surprised that 6 ran at all, the gap was bridged with ash.
My 88 has a maor vacuum leak that I haven't found so far. I've sprayed ether around all the usual suspect places.
Can someone furnish more detail about locating these ports, or even a picture?
Stuck open EGR valve?
Quote from: jim on February 03, 2012, 08:38:55 PM
Quote from: BenM on January 31, 2012, 11:15:48 PM
There are a couple of big vacuum ports over the 5-6 runner running accessories. Plug those and see if it makes a difference. I think 5-6 run cooler too, last time I changed plugs those two were fowled, I was surprised that 6 ran at all, the gap was bridged with ash.
My 88 has a maor vacuum leak that I haven't found so far. I've sprayed ether around all the usual suspect places.
Can someone furnish more detail about locating these ports, or even a picture?
It varies from year to year, but it's a screw in vacuum connector with 1-3 ports that sits on top of the intake almost at the back. Mostly it's for 4wd and the heater head unit, but some years there were extra takeoffs for spark-control or other operations. Sometimes it had a larger then 5/16 hose port, but if it's loose or leaky, or anything connected to it is, then there's a lean idle misfire in 6 and maybe 5.