I recently picked up a '99 v10 f250 with 158k. The coils and plugs were replaced with a rebuilt trans and torque converter feb/20 (8K ago). The truck is supposed to have a 5 star tuner/y pipes with 87/91 tow maps but I don't see a tuner or selector ****. It was installed by the original owner, PO didn't know anything about it except it was on the list when sold to him. I've got an email out the 5 star on where I should be looking for it.

I bought it and test drove it in the afternoon and it fired right up and feels strong. The seller pulled up right when I did and said it hadn't been started in over a week. I've noticed the last few morning start ups, it stumbles for a 1-2 seconds then idles smooth about 900 rpm. Mornings are not real cold here around low mid to upper 50's. The rest of the day it fires right up even after sitting for hours and getting completely cool (high 60s-mid 70s)

Started this morning, stumbled as usual so I turned it off after 30 seconds of initial start up this morning and it restarted just fine. I don't notice any colored smoke, very faint white but I'm guessing that's just moisture burning out from overnight.

I plan to take it in for a service, probably battery (4/19) and tires this week. I'm hoping to pull our 8k GVWR TT with it next week headed out to Williams AZ from Socal and would like to get this bug taken out of the mix.

Any input is greatly appreciated,

Matt

 

I took it into my local tire shop for some new meat and had them clean the throttle body but I am still having the AM stumble. Open to any ideas on where to start looking.

 

Here is a short clip of it starting up.
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Has anyone thought to check fuel pressure? The ECM doesn't really report the actual fuel pressure even though most scanners will have a "relative fuel pressure" PID---not the same as connecting the proper gauge and checking what the fuel pump is producing at the test connection port.

If below spec then you could be having fuel pump issues, the fuel pressure regulator could also be malfunctioning for those first few seconds. There are test procedures for testing the FPR.

 

I know the shop said they pressure tested the fuel pump but didn't mention anything about the testing the regulator so I'll look into the test procedures for it. Thanks for the heads up.

I was talking to a friend and he suggested I look into what sensor monitors engine temp since the issue only seems to happen when its cool outside. He was saying maybe the truck thinks it's warmer than it is cause that initial stumble after cranking but couldn't recall the name of the sensor. Any idea what controls that? Cylinder head temp sensor?

 

I pulled my IAC Valve and cleaned it out, was very dirty. I noticed it didn't have a spring on the shaft of the diaphragm, is this normal? I tore the gasket and bought a Standard IAC valve assembly for the gasket and noticed the spring on that unit. I stuck with the OEM IAC valve with and reinstalled but had the same issue.

Going to look into the fuel pressure regulator troubleshooting now.

EDIT: also pulled my MAF and sprayed it out really well. Appeared clean.

Initial idle rpm is 1100, then drops down to 950+-

 

That's pretty normal---my E-Series do much the same thing regardless of ambient temperature. Eventually it'll settle down to just about 650 RPM's while in Park. I believe that's a self-test of sorts the ECM performs on the sensors etc.

 

Did it help any? Sure sound like a carbon clogged IAC.

 

Good to know that's where it should be. Feels strong once I'm moving.

I feel like it runs smooth but didn't help with initial start up, it's doing the same thing for the same duration. I may just replace the whole IAC with another motorcraft because even after cleaning it seemed like it took some pressure to move the diaphragm up and down on the rod.

I just dont understand what moves the diaphragm/plunger back up without a spring on the stock setup.

 

So looks like motorcraft is no longer available from any auto parts stores near me. How do you all feel about the "Standard" brand for an IAC replacement? My only hesitation is the internal design looks different. Smaller plunger but does have a spring in teh assembly.

 

I used Delphi and a FOMO gasket.

https://www.ford-trucks.com/forums/1...l#post10502511

 

Nice, still running the truck? How was the reliability and function? I'm not sure how you got those pictures but well done, its tight back there. They were good to confirm the OEM doesn't have a spring, did the Delphi have a spring under the plunger?

 

Still working fine. I didn't see a spring anywhere, new or old, unless there is one inside the sealed solenoid section.

The old one just had a ton of carbon gunking up the plunger. I tried cleaning it, but still seemed sticky, so I bought the delphi from Rockauto.

 

That's great to hear. I returned the Standard brand to Oreilly's and plan to hunt down something on ebay or maybe I'll go with the delphi.

I installed a K&N intake system on the truck last night and when I fired it up today there was no lull/stumble. The only difference I can think of is I cleaned the outside temp sensor with the MAF cleaner, re cleaned the MAF sensor and disconnected the battery while doing the install. After install I drove it last night and did some WO straights to feel the system out. I'm going to check again early morning and see if I get the stumble when it's colder outside.

 

Also the tuner is not on the truck and I was planning on placing an order with 5 star (why I added the K&N now). The trans had been rebuilt and said " with HD internals" in the ad so I hit them up to get some specifics since its still under warranty incase that was info I needed to send 5 star's way. Well it sounds like it was just rebuilt, but when i mentioned a tuner the shop said that would void their warranty. Is this fairly common? I'm thinking that's why the tuner is no longer on the truck, probably removed for the rebuild or on advice of that shop.
Also, if the tuner is unplugged would the 5 star flash be reset to OEM ratios?