New Engine, still rough
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Trailering
Joined: Sep 2021
Posts: 19
Likes: 1
New Engine, still rough
Hello, I have a 92 F-150 with 320k miles, I just dropped a new engine in it because the original from the factory 5.0, lost compression on 4 cylinders, at the time with the old engine I was chasing an extremely rough idle, and frequent stalling, I resorted to throwing parts at it, then several cylinders lost compression. I said screw it, and bought a 0 mile rebuilt motor and dropped it in, the only issue is that it seems the new engine has inherited old tricks, it's still running rough. No stalling this time, but it definitely wants to during cold starts, the high idle kicks on very slowly, whereas before it would kick right up to 1100 and stay there until it was happy. I've gone through the checklist, spark plugs, fuel injectors, fuel pressure, fuel rails, map sensor, computer capacitors, I simply don't know what to test and probe, because I'm not trying to kill my new engine. Any advice at all would be appreciated.
Hotshot
Joined: Jun 2015
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What, if any, fault codes did you get before throwing parts at it? Did you get a code for the MAP sensor and if not why did you replace it? What lead you to replacing the capacitors? There have been threads here where replacing the capacitors did not help. The computer was still the problem. What fuel pressure reading do you get with the vacuum hose connected /disconnected? Finally, I assume you are using the old 302 firing order? Is that correct for the new engine or was a 302HO/ 351W firing order camshaft used in the rebuild?
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Trailering
Joined: Sep 2021
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What, if any, fault codes did you get before throwing parts at it? Did you get a code for the MAP sensor and if not why did you replace it? What lead you to replacing the capacitors? There have been threads here where replacing the capacitors did not help. The computer was still the problem. What fuel pressure reading do you get with the vacuum hose connected /disconnected? Finally, I assume you are using the old 302 firing order? Is that correct for the new engine or was a 302HO/ 351W firing order camshaft used in the rebuild?
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Trailering
Joined: Sep 2021
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To my knowledge it's the camshaft for an EFI engine
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Fleet Owner
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Trailering
Joined: Sep 2021
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Verified, it is correct for the regular 5.0 efi 1 5 4 2 6 3 7 8
On an unrelated note how badly would an engine run without the properly calibrated computer, you know how these trucks have calibration codes, if a 92 computer was running a 94 engine would it run poorly?
On an unrelated note how badly would an engine run without the properly calibrated computer, you know how these trucks have calibration codes, if a 92 computer was running a 94 engine would it run poorly?
Last edited by JohnHenryf150; Sep 6, 2021 at 07:05 PM.
Fleet Owner
Joined: Oct 2005
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From: Kentucky
1993 and earlier EFI trucks use the 1 5 4 2 6 3 7 8 firing order. 1994 and later (w/roller cam) use 1-3-7-2-6-5-4-8. Verify the plug wires are properly routed away from each other as well: https://www.supermotors.net/registry/media/470416_1
A 1992 5L truck computer will run a stock 1994 5L spec'ed truck engine just fine.
A 1992 5L truck computer will run a stock 1994 5L spec'ed truck engine just fine.
Thread Starter
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Trailering
Joined: Sep 2021
Posts: 19
Likes: 1
1993 and earlier EFI trucks use the 1 5 4 2 6 3 7 8 firing order. 1994 and later (w/roller cam) use 1-3-7-2-6-5-4-8. Verify the plug wires are properly routed away from each other as well: https://www.supermotors.net/registry/media/470416_1
A 1992 5L truck computer will run a stock 1994 5L spec'ed truck engine just fine.
A 1992 5L truck computer will run a stock 1994 5L spec'ed truck engine just fine.
Tuned
Joined: Dec 2008
Posts: 318
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From: Upstate South Carolina
As the new engine inherited similar problems to the old and the truck has 320k miles on it I'd look to some other basics. Just because of age I would change the ICM module for sure and potentially the distributor (simpler than changing the CPS inside it). I'm also assuming (bad word) you've done all the regular cleaning - TB, EGR, ISCV etc. Re-check/reset the timing.
Thread Starter
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Trailering
Joined: Sep 2021
Posts: 19
Likes: 1
As the new engine inherited similar problems to the old and the truck has 320k miles on it I'd look to some other basics. Just because of age I would change the ICM module for sure and potentially the distributor (simpler than changing the CPS inside it). I'm also assuming (bad word) you've done all the regular cleaning - TB, EGR, ISCV etc. Re-check/reset the timing.