Motor swap/upgrades rough idle, crank, no start when hot

red5.0fox

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Dec 1, 2019
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I don't use this a lot so hopefully I have the right thread here. Before I start, I do know about jrichker's crank no start checklist. I am running through that, but I wanted to see if anyone here had any ideas aswell (I'm also working for a little bit longer so I have to wait to go back to working on the checklist anyway). I just swapped out a bone stock 5.0L motor to a more well built 5.0. This motor has been rebuilt, GT40 heads, upgraded springs, rockers, explorer intake, 24lb injectors and MAF, aswell as a 75mm TB. This all from a bone stock motor. The issues I'm having is idle problems (believed to be timing, it also has a serious vibration when letting off gas but I think its all timing). Now the real confusing issue.. the car starts right up like a champ when cold, but once it's warmed up if it gets turned off, itll crank and crank but wont start. Here's what I have checked.. spark is confirmed good, definitely have fuel pressure (checked the schrader valve) and I can hear the fuel pump kick on, and I checked all of the grounds. I think it could be the ECT sensor but I'm not sure if it's the wiring or the sensor itself. Im getting a new sensor anyways, but when checking for continuity with a light on the wiring, its very dim. Is this how it's supposed to be? I also ran key on engine off codes and I got code 15. Apparently this could be because the battery was left disconnected for a long period of time and the motor may just need to run for 15-30 minutes to clear it all up? The computer was not messed with at all and worked fine with the last motor so I don't think its bad. I am a little stumped with this, so if anyone has some ideas feel free to chip in. Im going to try and get some more of this checklist done today. Thanks all!
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
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Ok, first you can't just push the needle on the schrader valve to check pressure, you need a gauge for a accurate reading,, and a test light won't help either, you need a digital volt/olm meter for the .5 volt reference to test stuff.
Go through the checklist step by step, don't jump around because the next step depends on the results from the step before. THE most important thing with computer controls is proper grounds, make sure they are attached in the right places.
 

red5.0fox

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Dec 1, 2019
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Hope Mills, North Carolina
Ok, first you can't just push the needle on the schrader valve to check pressure, you need a gauge for a accurate reading,, and a test light won't help either, you need a digital volt/olm meter for the .5 volt reference to test stuff.
Go through the checklist step by step, don't jump around because the next step depends on the results from the step before. THE most important thing with computer controls is proper grounds, make sure they are attached in the right places.
Okay, I don't have a fuel pressure gauge, I do however have a DVM. All grounds are in their stock locations, I did make sure of that. I'll try and complete the checklist some more and report back. I'm on paragraph 3 of his checklist, it's hard to advance from there because I'm not getting the no start issue unless its warmed up, and its really hard to keep it running long enough to get it to warm up. It'll start when cold and I haven't needed any ether for that.
 
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red5.0fox

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Dec 1, 2019
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Update, I followed some more of the checklist, cleaned grounds, I replaced the ECT sensor and fixed the wiring, and I haven't had the no start issue yet. Now Im tackling the other issues with idling. Right now it has a idle surge, and it absolutely reeks of fuel, its horrible. Sounds a little hesitant when blipping the throttle. Just because I could, I swapped my 24LB injectors with another set of 24LB injectors, and no change so that's been ruled out. I tested the fuel regulator, and its checking out aswell. Unplugging the IAC did nothing, and I also unplugged the MAF and nothing happened.. which I thought was very weird. Tomorrow I'm going to clean it and see if that changes anything. I also plan on setting the timing at the crank and hopefully that'll do something. It also sounds like it's misfiring. I'll double check the firing order aswell. I pulled this motor from another foxbody at the junkyard but I suppose it COULD be an explorer motor.. maybe its a non ho explorer motor? I have the firing order set for an HO motor. Any ideas?
 

90sickfox

Wasn't a pretty sight...and I've got big hands
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All explorer 5.0s are HO. It could be an f150, crown Victoria, or thunderbird 5.0, those would be the basic 5.0 firing order.

You can't get anywhere without the proper firing order or the timing set correctly with a timing light.
 

KRUISR

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Apr 16, 2015
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This motor has been rebuilt,
Rebuilt by yourself or you had a shop do it or some previous owner rebuilt it?

24lb injectors and MAF, aswell as a 75mm TB.
What MAF (brand) and is it calibrated for 24 lb injectors?

Unplugging the IAC did nothing,
What is your idle at once it starts?

Right now it has a idle surge, and it absolutely reeks of fuel, its horrible.
jrichker compiled a Surging Idle Checklist as well that is very good.

Cam change? If so, which one (model or specs)? When setting the timing, start with 10 degrees and get it running good first before advancing

With all these changes did you do a Base Idle Reset? I have a very similar combo and had some surging until I did that. I also cleaned my IAC REALLY good with brake cleaner (after I removed the solenoid part), cleaning as much soot out as possible and making sure the rod moves smooth and easy.
 

red5.0fox

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Dec 1, 2019
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Did you do a compression test?
No, have not. I'll put that on tomorrows to-do list. I'm going to triple check to make sure all the plugs and wires are good as well. Apparently there are possibilities of the harmonic balancer/crank pulley wreaking havoc on this stuff as well so I'll check that out just because I had to mess with that to do timing.
 

red5.0fox

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Dec 1, 2019
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Hope Mills, North Carolina
Rebuilt by yourself or you had a shop do it or some previous owner rebuilt it?


What MAF (brand) and is it calibrated for 24 lb injectors?


What is your idle at once it starts?


jrichker compiled a Surging Idle Checklist as well that is very good.

Cam change? If so, which one (model or specs)? When setting the timing, start with 10 degrees and get it running good first before advancing

With all these changes did you do a Base Idle Reset? I have a very similar combo and had some surging until I did that. I also cleaned my IAC REALLY good with brake cleaner (after I removed the solenoid part), cleaning as much soot out as possible and making sure the rod moves smooth and easy.
1. No, previous owner
2. BBK, and yes
3. around 1k
4. Yes, I've crossed some stuff off of it, still chipping away at it
5. I'm not sure since someone else did the build. I don't believe it does
6. I haven't done the reset, should I do all the other checks before hand? Also the IAC is still brand new
7. Thanks for your help!
 

Dan02gt

mazing how much gas smell came from that tiny hole
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Double and triple check for vacuum leaks. They can explain all the issues you are having.
 

Mustang5L5

Put lubricant all over the balls
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You typically get a Code 15 if you have the battery disconnected and just start the car and dump codes. You need to do a few cycles with the battery connected of starting the car, letting it idle, shutting it off, and then restarting it. Maybe go for a quick drive up the street and back and shut the car off and do it again. After a few key cycles without disconnecting the battery, then try and dump the engine off and engine running codes.

If it doesn't hot start, try depressing the gas pedal to the floor. This will put it in "flood clear" mode and not fire the injectors during the crank cycle. Be ready to lift off the gas if it does start.
 
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