Engine 5.4 dohc startup issues

Discussion in 'SN95 4.6L Mustang Tech' started by lushdog1984, Apr 10, 2013.


  1. lushdog1984

    lushdog1984 Member

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    ok question im totally lost. i just got my 5.4 dohc motor together and in my 01 gt. im getting fuel and fire but the motor isnt even hitiing. like i said im lost only thing i can think of is i forgot a ground maybe. ive ordered the right air intake so my maf will be properly hooked up but it still should have at least hit i imagine. anyways any input would be greatly appreciated.
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  2. trinity_gt

    trinity_gt Advanced Member

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    By fuel you mean the fuel rail is seeing ~40psi and the injectors are being fired by the PCM?

    By fire you mean the spark plugs are "sparking" and are doing so at the right time?

    You said you just got the motor together. How extensive a build was it? Did you install the timing components? How is the engine's compression? Are you sure you have spark --- is the ignition trigger wheel actually installed behind the timing cover?
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  3. Three50won

    Three50won Member

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    To add to trinity...what did the engine come out of? Did you swap the ECU?
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  4. lushdog1984

    lushdog1984 Member

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    the engine came out of a navigator. stock motor. no modds. just a direct swap and wiring harness mods. i already swapped the coil wires to make up for the difference in polarity. so im kinda lost. and i kept the factory ecu. everything fires at the right time. im thinking i havent grounded properly. i will do so later today. but still im dumbfounded. i have proper fuel pressure as well. ive even sprayed the motor with carb cleaner to see and it doesnt hit. so sumthing beyond me is up.
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  5. Three50won

    Three50won Member

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    It's probably the ECU...that's where I'd put my money. The 4.6 SOHC ECU is not compatible with a 5.4 DOHC engine. Get the Navigator ECU and it should fire right up. One other thing, if your car is a stick shift, then you'll need an ECU from a stick shift DOHC engine.
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  6. lushdog1984

    lushdog1984 Member

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    lemme ask you the difference then. i had a 4.6 dohc in it before i went to the 5.4. it ran fine with the 98 cobra motor i had in it no issues at all. is it that different with the 5.4?
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  7. Three50won

    Three50won Member

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    Ok, sorry it took this long to respond...rough week. I think you may have a little bit of confusion with the engines. A 98 Cobra does not have COP style ignition. An 01 GT does have a COP ignition. The ECUs are not compatible. The only way a Cobra engine would work in a GT with a GT ECU is if you removed the spark knock sensors, the IMRC plates and then you'd have to tune it. And if it were an engine from 98 and older, then you would have had to convert it to a COP style set-up if your ECU is 99-04...and vice-versa. So are you absolutely sure it was a 98 Cobra engine? Are you sure it was a DOHC engine? And yes, a 4.6 DOHC ECU will work with a 5.4 DOHC engine as long as you tune it with a tuner like Sniper which allows you to enter engine parameters. But again, the engine and ECU would both have to be either a 98 and older or a 99-04. DO you have any pictures?
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  8. lushdog1984

    lushdog1984 Member

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    i appreciate the info. but what i was saying is i am putting a 5.4 dohc from a navigator in my 01 gt. prior to putting in the navi motor i had a 98 cobra motor in it running fine. i swapped the 98 for a 5.4 dohc that had cop's. my ecu is the stock 01 gt ecu. i have all my sensors hooked up and everything. im just not getting a a hit when i crank over the motor. when i put the 98 cobra in all i did was change the valve covers to c head style covers and extended some wires and changed the polarity of the cop's to accomodate the dohc motor because i got dohc cop's. i dont have any picks yet but i will try to get some. i put a 01 cobra intake on along with the custom intake adapters i and a friend had made. we took his set of reichard racing intake adapters and had them remake them with a lil design change. nothing to effect how they match up to the ports but just outlining design. i have a 04 cobra throttle body, 19lb injectors factory 01 cobra fuel rail, spec stage 3 clutch hooked up to the 3650 trans. 4.30 rear with moser 31 spline axles. also have a champion radiator in it, and team z k member with coil overs. i cant even get it to backfire through the intake. had one backfire through the exhaust but that was it. i get great spark and fuel but its just not firing and firing orders on sohc and dohc mod motors are the same minus the new 5.0 and possibly the new 5.8. so for it starting up it should at least try or want to. so what can the issue be? i appreciate all the info you guys can throw at me. and if you ever know anyone needing intake adapter plates we paid 600 bucks to a machine shop to have them write the program to make them with there machine so lemme know. we can have them make you a set for around 375.00. as for it being a 98 cobra motor i helped take it out of my friends 98 cobra convertible and we dropped in his 5.4 dohc with 03 supercharger on it and then put the 98 motor in mine. im positive its a 98. as for the irmcs i had to take out the butterfly valves in them and plug the holes but that was it.
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  9. lushdog1984

    lushdog1984 Member

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    i have an extra 98 cobra ecu. i just dont have the cash at the moment to get everything flashed and the keys made. but i had the 98 dohc running with my stock ecu. dont get me wrong you could very much so be right. i hope your not lol but you very well could be. all i no is that when we did my first swap with the 98 cobra motor. we took out my gt motor sat the cobra motor in did some wire extending swapped valve covers so the cop's would fit reversed the polarity for the dohc cops swapped alternators and a few here and there little parts and pluged it up turned the key and bam it ran fine. but with this motor im at a loss cause it does nothing other then crank over lol.
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  10. Three50won

    Three50won Member

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    Ok, so I gather that the Cobra motor ran because as you said, you modified the ignition to COP and made all the other necessary adjustments so the GT ECU could run it. That makes sense.

    So with the 5.4 DOHC engine...what year Navigator did it come out of? Only other thing I can recommend is a system check. Check for fuel, spark, compression. Make sure the crank shaft and cam shaft position sensors are both plugged in. Check the ECU ground. And don't forget to check the PATS. You might have accidentally tripped it. I'll keep it on my mind and if I can come up with something I will let you know. I've done several engine swaps in my 03 including a 5.4 SOHC so maybe I will remember something useful...in the meantime, keep at it, I hope you get it started!!
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  11. lushdog1984

    lushdog1984 Member

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    the motor is an 03 i believe. i worked a ford dealership and got it on a takeout job. basically it had a blown headgasket. the persons insurance decided it would be cheaper to put a junk yard motor in rather then pay to have it fixed. i took in a blown up 5.4 and swapped them out for that. then put new headgaskets on and new head bolts.
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  12. Three50won

    Three50won Member

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    Any progress?
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  13. lushdog1984

    lushdog1984 Member

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    still nothing. i cranked her over and got a backfire through the exhaust again. think im gonna pull the fuel rail and double check everything. but thxs for asking
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