Rough/looping idle with ac on | Ford Explorer Forums - Serious Explorations

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Rough/looping idle with ac on


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August 9, 2021
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Year, Model & Trim Level
1993 Ford F-250 XLT, 351W
1991 Ford Explorer XL (mileage exempt).

Alrighty so here is the gist of my problem, when I bought the car the engine was trash, so I had my mechanic install a new motor in her, however he transferred and used all the old electric parts. To the new/used 100,000 mile engine (keep in mind that was the best that could be found in our area, the old engine was suffering horrific rod knock that the original owner drove for well over 80,000 miles).

Alrighty, whenever I turn on the vehicle she fires right up, however whenever I turn the AC on she chugs, her idle starts coming in waves, and you can visibly hear and feel the engine shaking excessively when in D and R when first moving, however with AC off she idles rather smoothly (although I do suspect one of the cylinders is misfiring). This and the fact it is only getting 10MPG and running extremely rich (with ac on or off). She is getting no O2 codes. So yesterday I installed a new ignition coil, and IAC valve. This actually did smoothen out the idle, but only when the AC is off. The main thing that is killing me is the gas mileage, I bought this car to be my economy car for my wife, my 93 F250 gets 9.5mpg on average.

I have 6 remanufactured fuel injectors on hand, as well as 6 new spark plugs, and a fuel pressure regulator (I have already installed 6 new spark plugs prior when getting the car). I am going to check for spark on each plug when I get home as well as the gap to see if there was a error on my end. (she has new wires). I am really trying to avoid pulling the throttle body off to get to the plugs. Part of me wonders if its a dying o2 sensor that hasn't been picked up yet. You can smell the gas coming from the exhaust. Another part of me wonders if I have a fuel injector or 2 stuck open. When my mechanic was switching my engine the new/old engine (it came from lkq pick and pull) it was running very rough, he discovered the engine had worn out fuel injectors so switched my old ones over to save me a dime (my decision which I am regretting now).

So I feel I am stuck on my course of action right now, and was curious if any of you have experience this before, and or know how to possible fix/find a solution for this.

Other than this the car is wonderful, beautiful red interior, clean, well kept on the inside, except for the arm wrest which have fallen apart, but not from neglect.

Thanks to any who can help in advance!!

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Clarifying, Is the smell coming from the exhaust actually the smell of gasoline or the smell of rich condition? If it is gasoline then that more suggests a no-fire situation.
Perform a fuel pressure test to confirm possibility of stuck open injector. Can also remove the plugs and cycle the fuel pump , smell/look at each cylinder .

Does the AC actually work? Work without excessive noise?Compressor shaft could be bent causing extra load at idle. Not highly likely but possible.

You might save yourself much diagnosis time by first opening up the PCM first to confirm there are no leaking capacitors. Seriously, consider this.

An aside, I have never heard the explorer referenced as an economy car.

Edit: Welcome to the forum.

To clarify a bit there is a strong smell of gas coming from the exhaust, and a slight rich condition smell coming through the ac vents when idling (nothing that would overwhelm the senses, just a slightly mild smell).

And yes the AC works just fine, in fact it runs cooler than my truck. The compressor and drier are both brand new. They replaced the older non functional unit. (which I later found out I was a dumb#### for buying when I found out the power plug for it was unplugged below the alternator. When I tried to get the new one up and running.) Tomorrow/day after I will try and locate the PCM to check the capacitors, will update you on that.

Thanks for the guidance!

While the recommendation to check out the capacitors stands as a matter having faith in your PCM just as a matter of age, if you are smelling unburned gasoline from the tailpipe with a smooth idle (sans AC load) and no codes (and you have verified that your MIL/CEL is illuminating at startup) then 1 or more stuck open injectors makes the most sense to suspect. To solve this I would start with the fuel pressure test. Also verify that the connectors/pcm is/are pulsing and not constant on with noid light .

If you are smelling the rich mixture through your fresh air intake, try to verify if it is coming only from the charcoal canister. If it isn't then you may also have an exhaust leak in the engine bay.

When driving , does the engine lope at all uphill/under extra load with the AC off?

About the misfiring cylinder, a common mistake made when changing spark plugs or spark plug wires from the distributor is to switch the fifth and sixth cylinders. For whatever reason, the cylinder order is 1-2-3-4-6-5. While this might not be the main source of the problem it might be a possible cause for a suspected misfire, especially since the spark plugs are new.

Update: Checked spark, it seems cylinder 6 spark was very weak. As well as 2 and 3. Also when verifying testing for spark found that passenger side valve cover gasket had gone bad since I got the engine and is leaking oil along the entire bottom side. Will be taking spark plug wires and using the lifetime warranty to replace and test again.

On side note very frustrated with rockauto right now, the fuel pressure regulator I had purchased stripped its threads immediately when trying to hand tighten the fuel line on it. Rockauto is forcing me to pay shipping on the return. Now im not going to say im never going to buy from them again because that would be a lie. They are to convenient sometimes. So for now I am going to reattach the old fuel pressure regulator and hope that it isn't bad. (I know how to test it, had to replace my trucks even when it was showing no visible bad test symptoms). I have also yet to pull the pcm, was planning to last night, but after a fit of rage of fighting the fuel pressure regulator for over a hour I was in no mood. It gets like that sometimes though. Planning on pulling it out tonight.

Having to wait on installing the new fuel injectors however until Saturday, no need to have to take apart the engine that far twice. Will update you on what I will break (probably vacuum line).

Note: forgot to add I did replace the pcv valve, but after fuel pressure regulator incident vehicle is in no running condition until reinstalled. Normal symptoms of non plugged in fuel pressure regulator would overshadow whatever fix the pcv valve would inquire.

cylinder 6 spark was very weak. As well as 2 and 3
Even your new ignition coil could be bad out of the box.
Your ignition control module could be suspect, but I think that would fail in coil pairs due to the way the EDIS operates. Not positive though.
Quick work to check for corrosion on the harness connector to the coil pack/ICM.
Before taking your spark cables in for replacement, consider swapping them between cylinders (length allowing of course) to see if the weak spark follows.
I've not yet had a negative experience with rock auto, being aware of the return policy but sympathetically crossthreading, stripping , needing Helicoils etc suuuxxx .

Consider not throwing new parts at this without being 100% on necessity. You've got a replacement engine with a new coil pack , new IAC, used fpr in place, used injectors you haven't confirmed are bad with pending new (remanufactured) ones , you can't be 100% are any better.