95 5.8 auto 119k. Still making it mine... Previous owner did a bunch of stuff to it.

So, I've been having an issue with what seems to be a misfire and a slight surging. At idle you barely get a hint of a misfire and the rpms fluctuate approx 100-200 rpm (hot and cold). Throttle (in gear at any point under load) it misses pretty bad. Let off the throttle it smoothes out. I've checked codes... As follows.

24-ACT or VAT sensor out of range
45-Thermactor air flow is always upstream during ERST.

I replaced the ACT (or IAT) and the ECT. No more CEL. But still missing. As far as I can tell there are no vac leaks. Cap, rotor, plugs and wires (plus more) all new. After a bunch of research I'm thinking it's got to do with the timing. I go to check the timing and TDC is on cylinder #4, dead nuts. Will this cause an issue? Is it required that TDC is on cylinder #1? If so do I need to re stab the distributor?

 

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well first off that year should be giving you a 3 digit code so something isnt correct with your 2 digit codes. Stock timing on your motor should be 10*btdc. many guys will do whats called a sixlitre tune up and bump the timing to 12*.

a vac leak will cause surging, as will a bad tps. If the vac lines are stock i would suggest replacing them with rubber lines.

TDC must be on cylinder #1 and your distributor rotor should be pointing to #1 post on your dizzy cap. so if this isnt happening then you need to pull and restab the dizzy.

are the plugs new and if so what brand/type. how do the plug wires look? is the coil stock?

 

The timing is squared away. I couldn't tell with codes, some seemed like they should've been 2 digit and others seemed they could've been 3 digit. Plugs are newer Motorcraft platinums, wires are newer super stock accels with heat protection by the headers, coil is aftermarket (accel). I had planned on swapping all vac lines to rubbers.

 

well the plat plugs are known to not perform well on our rigs. copper motorcraft or autolites perform the best.

I would also recommend going back to a motorcraft coil. make sure you have the plug wires separated and keep #7 & #8 wire from crossing/touching as those are prone to cross fire causing a stumble.

 

seeing how it hasn't been stated yet, did you pull the spout when setting the timing.

compression test would be good to rule out a bad cylinder.

 

Alright... So I swapped the plats for Motorcraft coppers and I happened to stumble across a half melted #4 wire (previous owner had done some of his own work to it) caused by it practically laying on the header. Fixed that. Tore the whole upper intake off, cleaned everything (throttle body, iacv and manifold were pretty caked in carbon deposits), replaced all vac lines with silicone, new pcv, new tps. Also checked the timing, again. Initial reading was, apparently, 26*btdc with the spout in cold. Let it heat up, shut it off, pulled spout and set the timing at 10-11*btdc. Shut off/restart spout in... Now the timing is at about 15-16*btdc. Is that normal for it to be higher with the spout in? Some sort of computer adjustment? It sounds and runs great.

 

Yes that’s one of the items the ECM controls.

 

Now my battery light is on... All the time. Battery gauge says everything is good. I took it to autozone to get the charging system tested and everything checked out. A poorly connected ground wire I'm guessing? It stalled once but fired right back up. Only issue now.

 

i believe there is a ground wire that connects to the upper intake. also one towards the back of engine to the body.

great work and yes the system advancing like that with spout plugged in is correct.