Have an 88 460 that will hesitate off idle if you just barely roll into the throttle. If you hammer it it will run out perfectly fine. Sometimes it will hesitate to the point where it just stalls out. Usually when it hesitates, if you blip the throttle it will come back. The other day it started up cold, went to high idle, then just died out for no reason a second later.
Fuel pressure is solid the whole time it's doing this. Have had both parts store and Motorcraft throttle position sensors on it. New fuel pressure regulator. New idle air control valve. New oxygen sensor. New Motorcraft map sensor. Cleaned the throttle body, new gaskets for the throttle body, idle air control valve, upper plenum to lower intake, and egr valve. Egr valve isn't stuck, even tried driving around with a block off plate on it. New plugs. Cleaned the cap and rotor. Ran injector cleaner through it. Capped all the vacuum lines except the map sensor and it ran exactly the same. Pulled the cover off the computer and didn't see any bad capacitors, actually looked like two of them had been changed at one point already. I wiggled on the top of the distributor shaft and didn't feel any play but I haven't had the distributor out.
Has an EEC code for the canister purge circuit but that's disconnected and vacuum lines capped.
I've checked the output of the coolant temp sensor and it's within spec.
It wants to stall randomly, hot or cold, so it must be something major that I'm missing...
It's getting a carburetor swap but I wanted to try and figure out what the deal is with this garbage before I strip it...

 

Did you pull codes from the computer?
That is where you want to start.
I dont see anything about you changing the TFI in the dist.?
It is the thing with all the wires going to it.
Lately I have seen them doing some crazy stuff. Some will heat up and stop working, no spark till they cool off and repeat.
Some will cause a miss or like you have a bog off idle or just no power.
They are cheap enough so would not hurt to swap it.
Dave ----

 

I was thinking of changing the TFI, hadn't noticed it's the distributor mounted version and not the better fenderwell mounted type... No codes other than the canister purge that's plugged off. Check engine light stays off, I don't think it even flashes on when it's hesitating. I just put a motorcrap coolant temp sensor in it because I had it on the shelf, still nearly shuts off if you slowly crack the throttle. Will the TFI usually throw a code or was it the pickup in the distributor that will usually NOT throw a code?
Thanks Dave

 

Not sure how related it is but most of the time the idle will kick up when going from park to drive or reverse. Always thought it was odd because it's a C6 trans so the computer has no inputs from it, other than seeing the vacuum difference from the load. The last couple times I drove it the idle didn't drop down so low when going into park.
Starting to think it's the computer but I didn't notice anything odd on the board.

 

Well you may be right as they moved the TFI from the dist. to the firewall or fender well by the FW?
It would be mounted to a heat sink to keep it from burning up.
I am pretty sure it is not the larger box type used with the DSII systems and 2 large plugs.

Again it would not hurt to swap it out and if that was not a fix keep the old one as a spare.
Make sure you use thermal paste on the new part to heat sink.

It would be the TFI that dose not throw a code at least I have not seen any codes posted for TFI's when they start to act up.
The dist. pickup coil (PIP) I have seen codes posted for it.
Dave ----

 

I would for S&G swap the TFI and see what happens.
But before you do that get the motor up to temp and check the timing.
You will have to pull the jumper to see if it is set to factory spec.
Then with the jumper in bring the RPM up and see if the timing advance any.
I believe it should and if it dose not well then change the TFI and test again.
Then road test to see how it runs if the same then ???
Guess it could be the ECM but I dont know how to test it more.
Hope someone will be by that dose.
Dave ----

 

Well I picked up a TFI module and a 5.5mm deep socket. Socket slides in all the way but won't fit the bolts, nor will any torx bits. So this may be continued LOL. Supposed to snow tonight and I need this pile to run right so I may just stop screwing around and plop the carb on it... This Electronic Failure Injection is starting to get expensive to make it run just as $#!tty as it did to begin with 😂

 

I decided to be an idiot and just plug in the new module and run it for just a second, seemed a little better and I can hear the idle air control valve operating more than it usually does. Does the IAC operate off of an input acquired from the TFI module or is that just a fluke? Still has a stumble if you barely crack the throttle when in park. Couldn't road test without the module attached to a heatsink, didn't want to get the module hot by running it more than a second... I dunno. I can get a computer from Autozone for 100 bucks, other than the pickup in the distributor that's the only thing I haven't touched thus far for it to still stumble.

 

Dave I might owe ya one sir, I got the right 7/32 socket (of course I'm working 15 miles from my shop) and got the new module on with a good coat of thermal paste. Road tested the thing around the block and it seems ok. Time will tell, as it seemed to be an intermittent issue. The no-load stumble off idle seemed to be better once it was warmed up, it's still there but I can't remember if these things did that normally when they were new or not. It's not really that bad I'm just used to snappy throttle response. If you can't tell I'm a carb and points ignition guy so I dunno LOL. I will try to keep posting in this thread if anything else happens, going to button things up and try to put a couple miles on it.
Thank you!

 

Ok so I drove it across town, the hesitation seemed to barely start coming back when it was fully warm after driving awhile. I decided to stick a NOS motorcrap TPS on it instead of the new Standard branded one that's been on it. I didn't really like how it went on, seemed like it was at the end of it's range before the throttle was at the end of it's motion.... Anyway I put the motorcrap one on and now it cuts out when you nail the throttle. I'm sure the computer has to "relearn" the different sensor, do I need to disconnect the battery and stand on my head three times or how long before it will be "normal"? Or has this been my issue all along?

 

It may be worthwhile to check TPS voltage out signal while slowly manipulating throttle to see if it has a weird spot just off throttle. I’m unsure of the 88 pin out but on my 91 the voltage out signal is the middle pin. I think “throttle closed” spec is 0.6-0.9V with WOT around 4.5V.

You can also check Ref voltage and make sure it’s 5V. But I would bet the TPS signal is more prone to intermittent problems than VREF.

 

Sorry folks I had my dingus move of the day... It helps to plug in the TPS after you install it. I plugged it in, unhooked the battery for a minute, and drove it. It seems to start better and run consistently so far. Very slight hesitation off idle but it's consistent and really not an issue. So long as it remains consistent I think it'll be good enough to drive. The TFI module was probably the intermittent issue. I got a USA made MasterPro unit, we'll see if it lasts. New parts are hit or miss anymore.
Thanks again