Dr. Jekyll... rough running 2.9

[brokencase]

Joe, those original wires look like a corroded mess.

No wonder you are having troubles. Make sure the big wire and it's connections from the alternator to the battery is in good shape.

[Ed Lijewski]

Several years ago a long-term Scorpio/auto trans owner/neighbor of mine lusted for a manual trans Scorpio. One eventually appeared on Craigslist in Washington state (we're in MD) near Seattle. My neighbor liked what he learned from contacting the owner of that manual Scorpio, especially as that owner said it was in good condition for a long road trip. So my neighbor and his wife flew there in late July to check it out in person and make the deal, with intent to drive it home to MD.

My neighbor wasn't a deep wrencher having done mostly simpler maintenance jobs, e.g. oil changes, brake jobs.. But that manual Scorpio was running okay, and the owner said the a/c had been recharged and worked good.

So they departed with the title and headed out east bound. A few hundred miles out on the Interstate the engine began to function erratically, losing power. My neighbor didn't know why that was happening, but it was too late to turn back towards Seattle, and his visual glances under the hood gave him no clues. So they continued on as best they could, finding it necessary to almost floor the throttle while keeping transmission in third gear to get enough speed to stay with traffic on the Interstate. Then entering South Dakota the a/c stopped cooling adding discomfort to their frustration.

After two+ days of dealing with the issues they arrived home.

A Saturday later my neighbor invited me to see his new purchase, which looked to be a decent buy from exterior and interior views, and then related to me the details of their saga bringing the car home (which I had not yet heard until then).

I had nothing specific in mind re the reason the engine ran poorly. He started the engine, raised the hood, and manually blipped the throttle to show how erratic and unhappy the engine ran.

I was going to check for loose/dirty electrical harness connections as the possible or contributing cause, but my eyes first fixed on the battery positive terminal bus wires there. I noticed one fusible link wire in very bad shape close to the battery, insulation missing as well as a few strands lost, with the other less so but also needing attention. So we spliced in 2 or 3 inches of new wire to those two, added new connection ends, and cleaned the battery terminals (temporary fix). Then my neighbor started the engine which ran fine, I got in to the passenger seat, and we went for a short ride proving full power and performance flexibilityhad returned.

I relate this experience to note how for FB MCA and/or MCA Forum members trying to help diagnose an engine issue from afar based only on symptoms can lead down paths that might not resolve the complaint. A visual underhood careful inspection as the starting point isn't only good practice but also might zero in on the main or associated problem, Starting the diagnosis with downloading computer trouble codes may lead to many parts replacing without resolving the original symptoms. Including photos of the engine and associated components (battery, alternator, fuse box, e.g.) along with a narrative is good practice.

YMMV

[andyofcolumbusmerkur]

What is truly sad is that the mechanic couldn't diagnose the problem or come up with a solution. This is probably the same with 99 percent of shops in the county. They will swap out a fuel filter, scan for codes. Scratch their head, suggest higher octane fuel or a fuel injector service for 300 bucks. Then one by one remove genuine Motorcraft parts that are working fine and replace them with new parts that may be of lower quality all while charging for the full shop rate. Bob's advice good. Parts cannon bad.

[Ed Lijewski]

What is truly sad is that the mechanic couldn't diagnose the problem or come up with a solution. This is probably the same with 99 percent of shops in the county. They will swap out a fuel filter, scan for codes. Scratch their head, suggest higher octane fuel or a fuel injector service for 300 bucks. Then one by one remove genuine Motorcraft parts that are working fine and replace them with new parts that may be of lower quality all while charging for the full shop rate. Bob's advice good. Parts cannon bad.

Just a surmise: from what Joe wrote it seemed he spoke to the mechanic, rather than having him check out the situation.

YMMV

[brokencase]

I relate this experience to note how for FB MCA and/or MCA Forum members trying to help diagnose an engine issue from afar based only on symptoms can lead down paths that might not resolve the complaint.

Agreed, but one can often make an assessment of what it NOT related to the problem. Thus avoiding someone from going down an expensive and laborious procedure that was not required.

A visual underhood careful inspection as the starting point isn't only good practice but also might zero in on the main or associated problem, Starting the diagnosis with downloading computer trouble codes may lead to many parts replacing without resolving the original symptoms. Including photos of the engine and associated components (battery, alternator, fuse box, e.g.) along with a narrative is good practice.

I don't know if photos are needed. Just ask the simple question "What are the state of the wires going to the battery?" before diagnosing a problem for someone. Important on the Scorpio as the positive battery terminal connection has been altered by previous owners, not to mention the age of the vehicles at this point.

But I must admit, wiring is fundamental to me. It is something I check as a matter of course and I take it for granted that someone else does the same. Given the condition of the wires shown in the photos, I am a bit surprised that Joe had not noticed the condition of these wires much earlier.

[Ed Lijewski]

My memory is that Joe implied more than once in separate posts that he didn't have confidence/experience dealing with electrical matters. Nothing wrong or even uncommon there for many; often that's just a characteristic of limited time or experience spent delving into identifying an resolving and issue.

For me from the onset of the narrative of this Scorpio's issues I took for granted that battery cables/wires/connections had been checked/serviced/maintained at least occasionally. I'm now, after years of Scorpio ownership, probably anal about checking those a few times a year, because I observed years earlier that both positive and negative connections would loosen slightly; a nut or bolt would need a half or full turn to firmly snug up a connection. And yes the Scorpio positive terminal bus bar, or a modification of it, would especially be included.

I think engine compartment photos accompanying opening narrative posts of a problem will always be helpful whether they immediately identify something amiss or not as they are part of the post record, and in taking them the poster may even realize an Aha Moment as e.g. corroded battery terminals, frayed wires somewhere, suspicious aftermarket wiring, etc.

On the fuel pump replacement, the Service Manual states unequivocally a determined value for fuel pressure. Neither XR nor Scorpio SMs say a pressure range is acceptable. 30 year old fuel pumps shouldn't be assumed to be ruled out of consideration in trying to resolve a persistent engine performance issue.

BTW, Joe had already focused attention to the alternator, had had it tested and it tested good, but the voltage regulator was bad and so he installed a new one.

YMMV

[andyofcolumbusmerkur]

He said the following
The car was towed to the shop I’ve used lately near my home.
- The old fuel was dumped, some fresh fuel, new fuel filter, fresh coolant, oil & filter. They felt the car was running better the more it ran. The thought was the injectors could be fouled up. Of course, their intake-injector service for $300+ was suggested. Nope - no guarantee this is the issue.
- They told me the ignition coil was checked and it was fine.

[Ed Lijewski]

He also said this:

I did talk to a friend who's a mechanic and he gave me some other ideas of what to check. So, the over-the-phone thoughts are and not in any particular order...
... check fuel pressure. I don't think this is it because the engine has tended to run ok once warm. I'll do just the same.
... one by one, pull the spark plug wires out & put back in for each cylinder and listen for any differences. Difference?... plug is firing. No difference?... something wrong, e.g., wire, plug, injector
... check for bad vacuum lines. I considered the canister while we were talking.
... PCV valve. I'll check parts list as I think it's new.
... are injectors firing? Check with a noid light which, of course, I don't have.
... exhaust smells. My friend suggested running the car and placing several thick layers of paper towels against the exhaust pipe. If it's black, too much fuel which could be a bad MAP sensor.
... compression test. I may have the line for this.

YMMV

[brokencase]

On the fuel pump replacement, the Service Manual states unequivocally a determined value for fuel pressure. Neither XR nor Scorpio SMs say a pressure range is acceptable. 30 year old fuel pumps shouldn't be assumed to be ruled out of consideration in trying to resolve a persistent engine performance issue.

The fact of the matter is the fuel pump replacement is an involved job and was not the culprit in this case.
I've measure my fuel pump pressure Ed, it was on par with what Joe measured. As stated previously the fuel pressure for the 2.9L on the Ranger is well defined online and is specified as a range and there is no difference between this and the Scorpio's 2.9L engine. Same injectors, same fuel pressure regulator, etc..

It helps to have an engineering background. To know that the flow through an small orifice is proportion only to the square root of the pressure across the orifice. So a difference of a few psi on the max pressure makes little difference on the flow of fuel through the injectors

It also helps to have actually disassembled a Bosch fuel injection pump and to understand it's inner workings. I have done so, their design is such that they don't fail by slowing loosing pressure over time. Typically they just stop running.