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Chasing down a hard start issue, 98 TC

LincolnJosh

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Hey all first time poster,

I have been having a hard start issue on my 98 TC and been trying to figure it out.

The issue had been intermittent at first, so I bought a new Motorcraft fuel pump. The issue went away for several months. Then appeared again a couple months back. I finally replaced the pump and thought that that would take care of the problem, couple days later after replacing the pump it started to happen with the new pump. Which leads me to believe it was not the old pump at fault and some other issue causing it.

As a side note, when I do get it started it runs perfectly fine until the car is shut off. Whenever the intermittent hard start issue is happening it seems to be more so during colder temperatures in the morning (currently 60-75 F) and starts fine during the hotter part of the day (90-100 F); but can not start once in a while during a hotter times. When the hard start issue happens it seems that I have cycle the key to on > off > then back to on and start it that way.

What I have done so far:
- Replaced pump
- Replaced plugs
- Replaced fuel filter
- Not sure if this matters, but EGR valve was replaced last year.
- Fuel relay replaced last year.
- Checked fuel lines and I don't see any leaks.
- Checked fuel pressure and it rests between 35-40 psi, which should be fine.
- Checked the fuel pressure regulator and it seems to be fine.
- Air filter looks good.

What I am planning on doing:
- Going to clean the TB and upper intake to plenum tube.
- Check IAC valve when I clean the TB.
- Check other vacuum lines ( recommendations on this one )
- Clean MAF sensor


Any other ideas if anyone has experienced this would be appreciated. This definitely has me scratching my head.
 

bmarler

New member
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there's probably a coolant temp sensor or engine temp sensor involved in the start functions to adjust the fuel mixture when the engine is cold. i'd have a look for that too.
 

LincolnJosh

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there's probably a coolant temp sensor or engine temp sensor involved in the start functions to adjust the fuel mixture when the engine is cold. i'd have a look for that too.
Thanks I need to check those, forgot about those sensors.
Would throttle position, crankshaft position and camshaft position sensors be good to check as well?

I managed to pull the TB and upper Intake tube. They covered up in carbon. This inherited TC is finally getting some TLC.
 

LincolnJosh

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So turns out my car and most other Lincoln TCs after mine don’t use a coolant sensor, instead the infer the reading off of the cylinder head temp sensor, which is under the intake manifold toward the front LH side
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bmarler

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Sounds reasonable. It's working ok? How about air temp sensor in the intake? Or air flow sensor? (just thinking about possibilities)
 

LincolnJosh

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I have yet to check those other sensors, reason I say the hard start is weird is that everything seems to run fine after it's started.

I will look into the forscan.
 

LincolnJosh

New member
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Do you have forscan software? It's really good for looking at all the input devices. And it's free...
Got forscan and a compatible scanner. It’s nice you can see all the input.

I guess the next item is what would be useful for this issue?

I was able to get the coolant temp off of the cht sensor output, which floats around 96-98C while warmed up and driving.

If I get those in here on a post I guess I would need to know what is nominal expected results for the sensor output.
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