Sorry for the delayed response I had a new line come in and it was wrong so I cut the hose and spliced it together with the proper barn. Ran the truck pretty hard with the regulator hook d up. Would idle at 32psi and under wot it would shoot up to 39-40. With the regulator unplugged it stays a constant 40 psi under work or at idle. The pressure does leak Down over night to 10 psi. I also noticed the missfire is more prominent when the lights are on.

 

Have you identified which cylinder is misfiring yet?

 

I have not I tried pulling plug wires while it was running good but I couldn't identify which one was actually misfiring

 

How closely associated is the misfire with turning the lights on?

 

It's pretty synonymous with the head lights. and en you turn them on it'll miss for a second especially when your driving then it catches it self and does it again. If I put my foot to the floor and gas it it moves pretty quick and the misfire goes away

 

Ok, you've confirmed that your fuel pressure is good, so....

The common possible causes of lean condition are:
-vacuum leans
-fuel system is weak/regulator is faulty
-injectors are not flowing property and/or are stuck closed

Rare causes are:
-o2 sensor sending faulty signal
-eec is faulty (would have other symptoms if this were the case)
-grounds/electrical; this sounds like it may be a variable in your equation, since electrical components (lights) seem to cause symptoms

So, you have essentially ruled out weak fuel pumps or regulator issues. Let's consolidate the info in the last 4 pages so we can deal with the remaining issues from here on. You checked, and double checked vacuum leaks, including egr valve, brake booster (not just engine side, but also cab side where the brake pedal push rod goes into the booster), vacuum reservoir canister (common to have rust holes in the bottom), vac lines, and intake gaskets?

Your fuel injector leak down seems ok, unless it drops immediately to 10 after shut down (leaky injector would cause rich condition 9 times out of 10, so even if this did occur I don't think it'd your issue). After confirming there are no vacuum leaks, the next logical (and cheap) step would be to test the injectors to see if they are all opening and flowing properly. This requires removing them and testing them with a pressurized liquid while energizing the injector solenoid. Also check the filters at the top of the injectors for clogs. When you do this test, order a full set of injector caps and o-rings, because you will undoubtedly break some pulling them out of the intake, having them on hand before you pull them out will prevent you from having to order parts before you get it back together.

Check all grounds, since it's a donor engine it's highly likely that a harness ground has been overlooked.

 

so at this point ive checked for all vacuum leaks, shes been smoked twice.
i replaced the egr with a block off plate and changed the pcv valve.
ive checked fuel pressure with vacuum and no vaccum and it checked out.
ive over looked the wiring for ground issues, cleaned all contact surfaces. i have a heavy duty negative lead battery cable that goes to a stud on the inside of fender where all my grounds meet up.
the misfire definitely shows its head more when the headlights or ac are on while the motor is cold.
i cleared codes again and im still pulling 41 and 91 both running lean codes.

so next step would be to pull injectors and check their performance?

 

Hmmm....a/c too eh? It may be that the additional load on the engine is magnifying the misfire, and not electrical/ground related.

Your situation at this point is diagnostic by trial and error, unfortunately. So, you've checked and re-checked vacuum and grounds, so moving on to additional free diagnostics is crucial, injectors being a logical next step to either find the problem or rule them out as a possible cause of your troubles.

 

So would it be in my best interest to just order a set off eBay instead of building a rig to test mine? Also I had my boss at work mention that it could possibly be the eec computer. What do you think? And what's the procedure to check o2 sensors. I'd like to find the problem before throwing any more money at it

 

Your problem certainly could be a bad eec, but it's highly unlikely considering it isn't showing any other symptoms besides the misfire.

Up to you as far as the injector replacement goes... if they're 25 year old injectors, then it wouldn't hurt to replace them anyway. If you do replace them, make sure it is a trusted source.

 

I think I fixed the misfire or it's not as bad at least. I reset timing to 10*. And it hasn't been happening much. I've been doing some reading on the lean code. And when I installed the motor I added a bung on the passenger side header cause I couldn't get the o2 sensor threaded in and my wiring diagram showed there's two o2 sensors. I read that there was only one 02 sensor and I'm thinking that's my issue with the engine running lean. Any thoughts? Or clarification

 

The 1990 Lincoln Town Car had a Left & Right 3 wire O2 sensor. 2 Sensors.

 

Color Code;
left; DG/Y-O/Y-BK/LG
right; DG/P-O/Y-BK/LG

 

Which means (maybe) since you are not getting a Code#42, one of your two O2 sensors is connected, and the other is not.

Your 1990 TC Computer/EECM is programmed to look for two O2 Sensors.

Are you still getting; "Code #75" - Possibly a connection no longer connected?

See post #25.

 

I am still getting code 75. I've visually checked that they're connected into the harness. How to i test the o2 sensors?