Rough idle and long crank

[nameskreen]

I have a 97 Mountaineer 5.0 with 210k miles. It has a slight rough idle but it runs great no hesitation or misfires, no check engine light. When it's warmed up, and I try to restart it, it cranks longer than normal. The coolant sensor is ok because my scanner reads 195 degrees when it's warmed up. The fuel filter, air filter and plugs and wires are new. I cleaned the EGR, MAF sensor and IAC. I poked around with a propane tank for vacuum leaks, my vacuum gauge reads normal at 19Hz. My fuel pressure gauge reads 31 lbs but drops rapidly to 0 after shut off(with in 30 seconds) I pulled the vacuum line off of the regulator and the fuel pressure went up to 40 lbs and no fuel spilled out of the vacuum line. I'm leaning toward a leaky injector but I'm not sure how to figure out if that is my problem. Any help is appreciated.

 

[ghosttrain2]

Next time you go to start it, cycle the key on and off a couple times before trying to start it, and see if that makes a difference. If it does, there is a check valve on the fuel sender that may be bad.

 

[nameskreen]

Would that cause a rough idle also?

 

[ghosttrain2]

maybe Seafoam in the fuel tank to help clean the injectors.It could also have a leaking intake gasket, I don't like using propane to look for vacuum leaks, have seen an engine go up in flames at a shop I was at.

 

[J_C]

No misfire codes set? I'm doubting a leaky injector if there's no misfires and would hook it up to a scan tool capable of live data to see what your long term fuel trims look like.

 

[azstang]

Did you ever find a solution to this? Having the same issue for the last couple months with a 2000 5.0 with 180K miles. Stumbles and feels like it’s going to stall at idle - but never has. I’ve been waiting for it to get worse or turn the check engine light on but nothing so far.

Only does it once it’s warmed up but otherwise runs great without any issue at all other engine speeds. All maintenance items are in check. Plugs and wires have 50K on them. Motorcraft IAC has 10K on it. No codes on scan tool and ECT sensor is reading correct. Fuel pressure is steady at 65psi at all times and only drops a little from that an hour after shutting down. Ran a bottle of Red Line fuel injector cleaner through it without any change. Have never touched the EGR or MAF but assume I would have a code for those if they were the problem.

Anyone have any ideas?

 

[nameskreen]

I still haven't figured it out. Mine had a slight rough idle warm or cold, but does not act like it is going to stall. Mine may have 2 separate problems. One causing the rough idle and one causing the long crank times when hot. Im just not sure

 

[974X4BLACKSPORT]

The fuel pressure should not drop to zero so fast after shutting off the vehicle, this is the same problem mine has, but intermittently. Fuel pressure in the rail is necessary after shutting off so that the next time you go to start the engine, the injectors give a "prime" pulse when the key is turned to "ON" just before the starter is engaged, this is necessary to give a fast clean start, but if the fuel pressure is "zero" in the fuel rail, then the "prime" pulse is inaccurate and can make the engine hard to start (as has also happened to my X). From what I understand, there should exist a check valve in the fuel pump to hold the pressure in the fuel rail after the engine is turned off, and because my Explorer also drops fuel pressure when the engine is turned off, I have a new fuel pump on hand ready to install when either the pump completely fails, or cooler weather gets here in Fl, which ever come first.

 

[nameskreen]

Yeah, I'm leaning toward fuel pump as my problem for the hard start. The pressure is good while it's running, that's why I think my rough idle might be caused by something else

 

[azstang]

Thanks nameskreen. Mine seems like it might have a bit of longer crank to start as well. I forgot to mention though that the fuel pressure is steady at 65psi at all times and only drops a little from that an hour after shutting down.

 

[azstang]

Figured it out. Connected to scanner the other day and found cylinder #3 had recorded a few misfires but not enough to turn the check engine light on. Everything else looked good. Pulled the spark plug on that cylinder and it was toast. It has some oil fouling going on in that one. Changed all eight and it's fixed. Will keep an eye on it going forward but with 180K miles it's probably about normal I figure.