Another new member from Metro Detroit

[VIIIain]

Hey everyone, I've been visiting this forum for a few months now but haven't introduced myself yet. I purchased a Garnet Red '95 Mark VIII LSC back in 2016 and it's been an absolutely fantastic vehicle for cruising around in every day. Currently it has 177k miles, and I'm in the process of getting most of the bugs ironed out. So far I've done a coil spring conversion, solid rear sway bar, spark plugs, 9mm wires, idle air control valve (ugh), oxygen sensors (ugh x2), fuel filter, and other basic maintenance items. I just recently graduated college and started my career as a powertrain engineer, and it was forward-thinking cars like the Mark VIII that inspired me to pursue a career in this field.

Recently the car's been bucking and stumbling under load, particularly at lower RPMs with the converter clutch engaged, and it's been getting difficult to turn over unless I prime the ignition a 2 or 3 times. My gut says fuel pump so I measured the pressure to be at around 30 psi at idle, but at WOT it wouldn't go above 37 or 38 psi. I can still drive it around normally, the problem only arises during hard acceleration like on ramps or passing. What do you guys think?

Thanks

 

[billcu]

Welcome to the Lincolns of Distinction!

Your pressure sounds ok, you should get around 40 at idle with the regulator vacuum disconnected.

It sounds like it might be a weak or intermittent spark problem to me. A couple weeks ago I had wet coil boots (gen 2) from all the rain we had. I've never seen wet spark plug wires near the plugs on a gen 1 before, but it might be worth a check.

 

[driller]

Welcome!

Sounds like fuel pump?

 

[VIIIain]

Thanks for the welcome guys, as well as the technical input.

Yeah, it was the fuel pump. It started making grinding noises this afternoon when I turned the key on. Seems fitting that it fails the day after I take interest in fixing it, but that's the Ides of March for ya.

Fortunately, RockAuto has a decent deal on a Airtex fuel pump/hanger assembly, it's designed and manufactured in the U.S. and has a warranty.

 

[billcu]

Strange, usually they just stop working. When you checked the pressure, was the vacuum disconnected from the regulator?

 

[steve]

Welcome

 

[redn8]

Welcome

 

[VIIIain]

Strange, usually they just stop working. When you checked the pressure, was the vacuum disconnected from the regulator?

I was parked at the time and I immediately shut off the car after I heard the clattering/grinding noise coming from the pump, fortunately I wasn't going anywhere important and I caught it when I was at home. If I had been driving it may have gotten to the "just stopped working" point while on the highway.

I did not measure the pressure with the regulator disconnected. That would give a more accurate diagnosis since it keeps the pressure constant at maximum, right?

I don't think it's an ignition problem, the power loss always happened as soon as it went below 15 MPG at freeway speeds and it gave codes 172 and 176 (lean on both banks). Anyways, the new pump should be installed by the end of next week. This new one puts out about 370 lb/hr(!), which gives me some room to grow in case I plan to swap in an engine from the Saturn V rocket.

 

[VIIIain]

So I replaced the fuel pump a couple weeks ago, that really improved the drivability while the engine was under load. There was still an occasional misfire at idle and low speeds once the engine was warmed up. You were right Bill, it turns out the 9mm Ford Racing ignition wires I installed over the summer were arcing at low engine speeds. I've replaced them with Motorcraft OE spec wires and it runs as good as new, from 600 RPM to 6000 RPM.

Lessons learned: Don't overpay for lousy quality, no-warranty parts because they say the word 'Racing'. And don't rule out that an engine problem could be caused by both fuel and spark deficiency.