90 Town Car chugging at idle when warm?

[drhill]

Hi everyone,

Well, just got done doing a head gasket on my 90 town car 5.0....everything went very well, fired right up after I figured out the timing. runs great when it's cold but once it worms up it idles rough especially in gear...kind of like a chugging. Doesn't stall out. Exhaust smells a bit rich. Drives great and runs great off idle. I pulled codes and here is what I got: 41, 91, 33, 74. I ran a cylinder balance just in case - it came up even. Plugs, wires, cap and rotor are all in good shape.

My first thought was a vacuum leak but I couldn't find one....pulled all the vacuum lines from the manifold and plugged the manifold...still the same...maybe "slightly" better. I sprayed all the connections and seals with carb cleaner...no change.

As a side note, I had a decent amount of oil smoke puffing from the pcv and oil fill cap when I pulled the manifold vacuum from that system. As in, I wouldn't want to just have breathers on this car.

Any other thoughts?? As always I appreciate the wisdom!

[gadget73]

41 and 91 are system lean codes. If it runs rich, but shows lean, my guess is a fault with the air injection stuff. If that is pumping air into the heads all the time, it will fake out the oxygen sensors and cause the ECM to dump more fuel to fix the "lean" condition. Try just pulling the belt off the smog pump to see if that clears up. it will give a 44 and a 94, but if it runs better at least you'll have a place to start.

33 is EGR not opening. Could be a vacuum problem, and it could be related to a possible air injection issue. Make sure those lines over at the smog solenoids are where they belong. If something got mixed up, that might explain all of this.

[drhill]

thanks Gadget. Most of the original plastic vacuum tubing is present and in good shape so that makes routing everything much easier. I did find a disconnected vacuum hose with a check valve that is inline with the smog solenoids...hopefully this helps! I would think the solenoids can't open the valves at all without vacuum but....I'm no expert.

This would also explain why the idle got slightly better when I disconnected (and plugged the manifold vacuum port) the distribution block. That is where this line and check valve tee'd off from. Weird vacuum routing on this car compared to a traditional box...not nearly as straight forward but they seem to have reduced the quantity of lines.

If I don't see a fix, I'll pull the belt and see what happens. Also - I have heard disconnected and bad grounds could cause this....there seems to be one ground from the back of the engine to the firewall...looks original and in good shape...

[gadget73]

Oxygen sensors can fail like this too, but I'd want to be sure its not a fault somewhere else first. A stuck diverter valve could also do this. Popping the belt off the smog pump would eliminate any possibility of faults with that system. If it clears it, then you'll have to do some more poking around to figure out whats going on. Those valves really aren't that complex to figure out. No vacuum to the bypass valve pushes air through the hose. Vacuum on the valve dumps it to air. The diverter valve switches from one side to the other depending if you have vacuum on or not, though I don't know which end its supposed to come out for which condition. basically if you can put a vacuum pump on it and switch which hole the air comes out of, its working. Might be easier to pull those off the car and just blow through them for testing.

[drhill]

Ok, I ran with no smog pump/ac belt. Same issue, no difference. I also ran codes - same exact codes 33, 41, 91 and 74 only when KOER. It does seem like these codes are probably a related problem right?

[gadget73]

ok, so not smog related, cool. 74 is you didn't step on the brake pedal when it expected, ignore that one.

33 is EGR valve not opening
41 is system lean
91 is system lean

I don't remember which is which, but 41 is for one bank and 91 is the other. Since its showing on both, it says the whole thing is lean. Check the fuel pressure, if thats low it will do this. Large vacuum leaks can do it too, or if both sensors have failed in a strange way. Oxygen sensors usually do not give codes when they quit though. A large vac leak could explain the EGR not working, but a small leak anywhere in the plastic tubing on that particular circuit could do it too. Make sure the vacuum tree isn't cracked. Maybe just pinch off the hose feeding to it to see if it changes how things run. If there is a serious leak there, I expect that you'd notice an immediate change in idle by closing it off.


Also, simple questions, the timing is set correctly, and the plug wires are connected properly ? #1 on the distributor goes to cylinder #1 too right? These get funny if the distributor isn't clocked right. Are the gaskets between the EGR spacer and the intake and throttle body new with the head gasket job, or were those parts not disturbed? If they are new, make sure they went in right. I want to say if the two got mixed up, you'll get EGR leakage around the gasket and into the throttle body. It can leak coolant from the spacer into the motor too, so make sure its not pissing green juice into the throttle body if the cooler lines are hooked up. Make sure those aren't actually connected to a vacuum port. it will run fairly stupid with direct coolant injection to the intake.

[drhill]

Thx for the tips! I have actually covered most of these bases I think:

- I have thoroughly checked for vacuum leaks at the ports on the upper intake. I pulled all the lines attached to the upper and capped...no difference...so that hopefully ruled out the plastic vacuum tree and any of the other vacuum related items throughout the car. I even complete disconnected pcv and no change.

- upper/EGR/TB was all taken out in one piece - no new gaskets there.

- I moved the engine accidentally while the dizzy was out so I found TDC the old fashion way...finger over #1 cyl plug hole...air blew out and timing marker was right near 0 deg. set it to 10 BTDC with spout connector out. Yes - #1 terminal on cap is connected to #1 cyl on the car

- spark plug wire routing was checked three times to make sure!

- fuel pressure at 32 psi at idle with vacuum to FPR...a tick over 40psi with vacuum disconnected at FPR

- it runs and drives great other than the idle fumbling (at it's worst in gear)

- I did connect TB coolant passages correctly - and no white smoke from tailpipe


The head gasket was truly toast when I replaced it - big chunk out between all back three cylinders on driver side - none of them were firing. Cylinder balance test caught it on the first go around. I just remembered that I also had code 33 for the egr before I did the head gasket - but no 41/91 code at that time. so that kinda leads me to think I screwed something up during the teardown and install to cause 41 and 91? I was thinking maybe running it with blown head gasket for a while might have fried the o2s but unlikely because they were working fine just before teardown.

Also - just fyi - this is a MAF car from California for whatever that is worth.

I had the o2s both not grounding in my 5.0 HO MAF converted wagon and it ran much better than this lincoln. 02s in that car were not giving any feedback to the ECM. I really only noticed the bad hwy mpg in that car until I fixed it. I would think the car would still idle well even without o2s working.

Maybe coolant temp sensor? Or would that throw different codes?

Gosh this just feels like a vacuum leak somewhere but I can't find anything! I hope nothing is wrong w intake gaskets...and I also hope nothing is wrong with the other(pass side) head gasket. All of those cylinders checked out fine so I didn't replace it.

[sly]

I wonder if it's 180 out (dizzy vs crank). Cyl 1 TDC will happen for both exhaust and intake strokes, but the timing is only for one of those.

[gadget73]

don't think it will even run if its 180 out. I've done that before, usually it just backfires an does really dumb stuff.

hmm, MAF car, no chance there is a crack in the air tube between the MAF and throttle body is there? The tube from oil fill neck to the throttle body is installed? MAF stuff gets goofy with unmetered air.

If the head gaskets were that bad, it may have taken out the oxygen sensors. They will fail if they have gotten fouled with coolant.

Is the IAC working like it should be ? If thats not opening up it can make it idle low and rough.


Coolant sensor or air temp sensor might be it, and they can sometimes go in a way that doesn't produce codes. If they output a value that is wrong, but not outside of the normal range it might be it. You'd have to use a meter and compare their readings to the chart.



The coolant and air temp sensors have the same values as far as I know.

[drhill]

ok, coolant and air temp sensors are reading correctly voltagewise. Couldn't seem to get the resistance test to work right, but that's likely me and my crappy meter. air tube is fine after the maf. oil fill to TB tube is hooked up and in good shape.

IAC doesn't seem to do much if anything when I unplug it? I revvd and let it go back to idle...same as before? My experience has been that they usually help keep the car from stalling in this scenario. I'll try to swap it for a know good one.

I'll have the car in the air early next week so I can try to test the o2s...I'm sure they're not switching but I can check anyway.

Other than that?

[gadget73]

normally with the iac unplugged, it idles around 500 rpm. if the screw is wound in too far, it may not be able to work right. It could also be bad and someone screwed in the throttle stop to fake out the bad part. High TPS voltage is a clue that might be the problem. A bad TPS also makes it idle funky, depending how it failed.

[cld783]

It should barely idle if not stall when you unplug the iac. Unless the throttle stop has been screwed in too far (or vacuum leak somewhere) like gadget said.