PCM vs. ECU
Senior User
Joined: Jan 2012
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Thread Starter
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Cross-Country
Joined: Feb 2020
Posts: 54
Likes: 0
Hey man,
I know this thread has been dead for a few years, I have been running the same truck discussed in the thread but to refresh your memory. I have a 94 f150, the original motor was the 302 and I swapped for a 351 from a 1991 bronco. I need to get a new ECU, the rock auto one you linked is long gone, I never got around to ordering it... I am looking at ordering one from Oreilys because they have remanufactured ECUs from cheaper than the other sites. If the truck and the sensors are from 94 I should need a 94 correct? The pinout of a 91 ECU wouldn't fit correct?
Sorry for the repetition, I just need to pass emissions and ECUs are expensive for a college student.
Thanks,
Michael Oliver
I know this thread has been dead for a few years, I have been running the same truck discussed in the thread but to refresh your memory. I have a 94 f150, the original motor was the 302 and I swapped for a 351 from a 1991 bronco. I need to get a new ECU, the rock auto one you linked is long gone, I never got around to ordering it... I am looking at ordering one from Oreilys because they have remanufactured ECUs from cheaper than the other sites. If the truck and the sensors are from 94 I should need a 94 correct? The pinout of a 91 ECU wouldn't fit correct?
Sorry for the repetition, I just need to pass emissions and ECUs are expensive for a college student.
Thanks,
Michael Oliver
Lead Driver
Joined: Oct 2016
Posts: 6,185
Likes: 633
From: Houston/Sugar Land
Hey man,
I know this thread has been dead for a few years, I have been running the same truck discussed in the thread but to refresh your memory. I have a 94 f150, the original motor was the 302 and I swapped for a 351 from a 1991 bronco. I need to get a new ECU, the rock auto one you linked is long gone, I never got around to ordering it... I am looking at ordering one from Oreilys because they have remanufactured ECUs from cheaper than the other sites. If the truck and the sensors are from 94 I should need a 94 correct? The pinout of a 91 ECU wouldn't fit correct?
Sorry for the repetition, I just need to pass emissions and ECUs are expensive for a college student.
Thanks,
Michael Oliver
I know this thread has been dead for a few years, I have been running the same truck discussed in the thread but to refresh your memory. I have a 94 f150, the original motor was the 302 and I swapped for a 351 from a 1991 bronco. I need to get a new ECU, the rock auto one you linked is long gone, I never got around to ordering it... I am looking at ordering one from Oreilys because they have remanufactured ECUs from cheaper than the other sites. If the truck and the sensors are from 94 I should need a 94 correct? The pinout of a 91 ECU wouldn't fit correct?
Sorry for the repetition, I just need to pass emissions and ECUs are expensive for a college student.
Thanks,
Michael Oliver
I show O'Rileys has it in their website as part number 78-5848 1994 Ford F150 5.8 manual transmission. For ID# F4TF-AHA...... Another selection depending is , 78-5849 For ID# F4TH-AHB Same configuration as above but different ID#
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
You need a computer (PCM) for a 1994 F150 w/5.8L engine and a manual transmission. Do not source an earlier version, it will not work well with the computer controlled dwell (CCD) ignition system your truck uses. 1994 was the first year Ford started to use this type ignition on the F-Series/Bronco gas engine trucks.
You may be able to use a 1995 PCM as long as it is for a F150/Bronco with a manual transmission. If you try to use one for a F250/350 the emission system is different and may cause a CEL. So if you are going to spend money get the 1994/95 for a F150 and manual transmission to keep the headache level down to a minimum.
You may be able to use a 1995 PCM as long as it is for a F150/Bronco with a manual transmission. If you try to use one for a F250/350 the emission system is different and may cause a CEL. So if you are going to spend money get the 1994/95 for a F150 and manual transmission to keep the headache level down to a minimum.
Thread Starter
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Cross-Country
Joined: Feb 2020
Posts: 54
Likes: 0
Hey, wanted to pick your brain some more... I bought an ECU from Oreilly's Part # ECC319... link: and I installed it into my truck. When I turned her over the engine did start but idled very poorly and was on the verge of dying from such a low idle. The timing advance was also off and the engine would stall when I stepped on the gas. Is this a timing issue? is this idle air/ throttle body. I was looking at the firing orders in my Chilton manual and they didnt match up with the sticker in my truck, however the last ECU ran the same timing as the engine and seemed to do fine. What did I do wrong here? should I play around with the distributor some more before taking it is. Is it possible this ECU has the wrong firing order? Also might there be an issue with my distributor cap order?
Any help appreciated
Michael Oliver
Any help appreciated
Michael Oliver
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Fleet Owner
Joined: Oct 2005
Posts: 20,789
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From: Kentucky
1994 and later 5L trucks and all EFI 5.8L engines use the same firing order 1-3-7-2-6-5-4-8. Did you change or mess with the base timing before changing the PCM? Have you verified the base timing with the SPOUT plug removed?
What distributor did you use for this swap? A 1991 has a distributor mounted Ignition Control Module (ICM). 1992 and later trucks use a remote mounted ICM.
What distributor did you use for this swap? A 1991 has a distributor mounted Ignition Control Module (ICM). 1992 and later trucks use a remote mounted ICM.
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Cross-Country
Joined: Feb 2020
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I have a 1994 compatible (with the heat sink mounted control unit) Dizzy which had compatible cam gear material for the 1991 engine, I don't have a link for you but it was working well with the other ECU from before (5.0 L). I didn't touch the timing at all before swapping the ECU in fact the ECU swap is what caused me to go into this whole mess. I finally found the timing marks and currently have the timing set to about 20 BTDC (in the manual it said 10) because everything else felt awful and when the engine came back down off the throttle it bogs hard. I am not convinced the the timing pointer is stock and or accurate but my other thought is idle air control. The previous owner did mods so a stock ECU might not run it correctly however maybe by increasing my idle air supply I can prevent the bogging? thoughts? Also i did find the POUT plug and removed it though I don't understand what that is or does. It was located by the ECU plug and the brake booster on my truck. Gray plug removed for timing light and replaced for driving.
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
Base timing is 10* BTDC with the SPOUT out. Removing the SPOUT takes the computer out of the control loop. Same concept of removing the vacuum line from the vacuum advance on the distributor for carb.'ed vehicle. The Ignition Control Module (ICM) should be a black Computer Controlled Dwell (CCD) version for 1994 and up F-Series trucks and Broncos. If you have a gray Push-Start ICM it can cause driveability issues. Aftermarket ICMs can also be problematic.
If this "new" PCM is causing issues then reinstall the old 5L version to see if the new symptoms go away. If they do then you may have a bad PCM. These rebuilt fuses they sell these days are a crap shoot unfortunately.
If this "new" PCM is causing issues then reinstall the old 5L version to see if the new symptoms go away. If they do then you may have a bad PCM. These rebuilt fuses they sell these days are a crap shoot unfortunately.
Tuned
Joined: Jan 2021
Posts: 377
Likes: 81
Base timing is 10* BTDS with the SPOUT out. Removing the SPOUT takes the computer out of the control loop. Same concept of removing the vacuum line from the vacuum advance on the distributor for carb.'ed vehicle. The Ignition Control Module (ICM) should be a black Computer Controlled Dwell (CCD) version for 1994 and up F-Series trucks and Broncos. If you have a gray Push-Start ICM it can cause driveability issues. Aftermarket ICMs can also be problematic.
If this "new" PCM is causing issues then reinstall the old 5L version to see if the new symptoms go away. If they do then you may have a bad PCM. These rebuilt fuses they sell these days are a crap shoot unfortunately.
If this "new" PCM is causing issues then reinstall the old 5L version to see if the new symptoms go away. If they do then you may have a bad PCM. These rebuilt fuses they sell these days are a crap shoot unfortunately.
Your truck is/was a 94 f150. Did/does it have a MAF sensor?
Did you pull the 91 351 from the doner?
Which wiring harnesses did you use when putting the 5.8 in your truck?
You said the new motor ran fairly good with ECU/EEC from that was in your truck, correct? But now that you need to get emissions and have a new ECU it idles like poop, Where did the new ECU come from?
You also mentioned that the PO removed some or most of the emissions components from the 5.8.
There are a lot of bits of information that need to be sorted out.
Can you confirm the Catch Code from our original ECU and the new one?
This whole 5.0 to 5.8 swap can be much trickier than it sounds. I know, I am in the tail end of doing it. I also have learned a ton of info the hard way on this as I also did the MAF upgrade.
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Cross-Country
Joined: Feb 2020
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I believe it is a speed density sensor instead of MAF. I used the original wiring harness from the 5.0 the original alternator from the 5.0 (this weird configuration required a different sized belt which I lucked out on, can't believe it still runs to be honest. And the ECU I had been using was also from the 5.0. I did pull the new 5.8 from the bronco myself. I had to use the original wiring harness so I changed the distributor to a 1994 style and I kept the alternator the same like I said. the new ECU is linked earlier in this chain and is from Oriellys. Bought it Remanned so maybe it is that. I will reinstall the old ECU to check it could just be a bad ECU, the timing should not depend on the ECU at least not the base timing, so unless the timing advance was particularly different between the ECUs it shouldn't have been so bad... Sad to hear about poorly built Remanufactured parts, I kind of rely on those...
Lead Driver
Joined: Oct 2016
Posts: 6,185
Likes: 633
From: Houston/Sugar Land
I believe it is a speed density sensor instead of MAF. I used the original wiring harness from the 5.0 the original alternator from the 5.0 (this weird configuration required a different sized belt which I lucked out on, can't believe it still runs to be honest. And the ECU I had been using was also from the 5.0. I did pull the new 5.8 from the bronco myself. I had to use the original wiring harness so I changed the distributor to a 1994 style and I kept the alternator the same like I said. the new ECU is linked earlier in this chain and is from Oriellys. Bought it Remanned so maybe it is that. I will reinstall the old ECU to check it could just be a bad ECU, the timing should not depend on the ECU at least not the base timing, so unless the timing advance was particularly different between the ECUs it shouldn't have been so bad... Sad to hear about poorly built Remanufactured parts, I kind of rely on those...
Tuned
Joined: Jan 2021
Posts: 377
Likes: 81
The ECUs are actually much more complicated than many folks believe. I took the challenge/made the mistake of stepping into the world of tuning my own. The cam I wanted was too radical for a SD type engine and was of the 15426378 FO family so I didn't have much choice. This being said, you need a computer for a 5.8 and the proper transmission, They store displacement info, injector curves, mainfold pressure curves, timing tables, Shiftpoints IAC parameters and sooooooo much more. There is also the issue of pin outs between different ECMs. All of the EECIV years will hook up, but there are many different pin configurations between them.
It would be nice if it was as easy as pulling a 5.0 and dropping in a 5.8, like it was back in the days without EFI and computers, but the simple truth is, it is not.
It would be nice if it was as easy as pulling a 5.0 and dropping in a 5.8, like it was back in the days without EFI and computers, but the simple truth is, it is not.