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Discussion Starter · #1 ·
ive heard different things from different people maybe you can help. non HO's came with flattop pistons and it is not possible to run much larger than a stock HO cam due to valve to piston clearance issues. is there any truth to this. also im having problems with my check engine light coming on and a very rich smell during startup. what im told is that is because i have a non-HO longblock with an HO intake, computer, and (what they say is the problem) map sensor. is that the problem or is it something else.
 

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Non HO motors use a different firing order, so you needed to swap in the factory HO cam and all the goodies needed to convert to a roller cam (though some later model non HO had a roller cam too)

Though it does sound like you have done at least the cam conversion.

What could be hurting you is running this setup with a speed density computer.

The HO speed density computer is pre-programmed to assume a known pumping value of the motor. This replaces the role of the Mass airflow and uses the MAP sensor and RPM to calculate airflow.

The problem is that you have the even more restrictive NON HO Non E7TE heads and different pistons. Therefore you have less airflow than the computer is calculating, and less compression too. This is possibly causing come of your rich fuel/air problem.


This is assuming that everything else is working. You should check your computer for codes to see what is causing the MIL to come on.

I am fuzzy on one thing you may be missing, a cam sensor. The HO is a SEFI system which times the injector pulse with the intake valve opening. At least with my 4.6 there is a sensor on the camshaft sproket which times the injector with the cam. The HO should have this too but not certian if the Non HO does not have that, IIRC the NON HO has a speed density batch fire system.

FWIW I had a bad cam sensor in my 4.6 but still passed emmissions ok.
 

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Yes, you can get in to P to V issues with flat top pistons and a high lift, or large duration, cam. What injectors are you running? Did you install the injector connectors to reflect the non-HO firing order? BTW, the HO cam isn't all that bad.
 

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Discussion Starter · #4 ·
it still has the non ho cam. the intake, injectors(i belive), sensors, ecu, etc. are all HO. the firing order is where it gets fishy. i checked the firing order and it doesnt match either HO or non-HO. when i set it to non-HO order it ran like crap and when i set it to HO order it backfired really bad and wont run at all. i put it back to how it was and it worked fine. as far as the injector connectors i couldnt tell you
 

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What you need to due is put in the non ho computer and injector harness or it will never run right either that or get a ho cam and crankshaft trust me My buddy put no ho cam in my mustang and I played hell trying to move injector wires and all kind of crap finally I put in ecam moved injector wires back to normal and now its perfect
 

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If your setup is speed density, then your MAP sensor should be OK - I compared part numbers once between my '87 5.0 HO and an Escort, and they were the same. Seems Ford didn't make too many variations of the MAP sensor.

The non-HO cam can be made to work, but you must re-connect the fuel injector plugs to the injector for the cylilder that is set to fire. First, route your plug wires for the non-HO firing order. Both cams start with # 1 cylinder, so that injector harness is plugged in correctly. After that it starts to get complicated. Example: If the second cylinder in the HO firing order is # 3, and the second cylinder in the non-HO firing order is # 2 (may not be true, I don't remember the non-HO firing order), then the injector harness for # 3 must be moved to # 2 - and so on...

Remember, Ford counts their cylinders front to back, 1 to 4 down the passenger side, then front to back, 5 to 8 down the driver side. Good luck.
 

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I have some info on my site about firing order.
With Speed Density, the MAP is pretty important. If the cam is too different than stock it gets confused. Yours sounds too mild, not too hairy. The nons use 14 lb injectors, while HO use 19. Too much gas, but the O2s should adapt a certain amount. Maybe a Tbird computer would work.

The cars are all sefi, with no cam sensor.
 

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Discussion Starter · #8 ·
dont know if i was specific enough before but all it has that is non-ho is the long block (block, crank, rods, pistons, cam, heads) out of an 87 crown vic. everything else is 90 LX HO. it is mass air and and the HO intake and all the sensors, ecu, etc. checked it out today and the firing order is non-HO. also the check engine light only comes on after ive been driving for a while.

as far as the cams go what is the biggest that anyone has or has heard of run with the flat top pistons.
 

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WESBOB 89 said:
What you need to due is put in the non ho computer and injector harness or it will never run right either that or get a ho cam and crankshaft trust me My buddy put no ho cam in my mustang and I played hell trying to move injector wires and all kind of crap finally I put in ecam moved injector wires back to normal and now its perfect
I thought the crank throws were in the same places, and only the camshaft was different as they swapped order on a few cyls. I know on some other motors this can be done without a diff crank.

If I am wrong about this, then you can't run the motor with the HO system even with the HO cam. The cam and crank have to match up or you will slam a valve into a piston for sure.

Like I had posted before the HO is a SEFI system and times the injector pulses based on the camshaft rotation. Since the camshaft has a diff firing order, it's squirting fuel at a closed Intake on some cyls and hence not running right.

You need to swap back to a NON HO computer harness to make this thing run.
 

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I have even tried to search some info on the HO vs Non HO cranks and have come up short. I know there were different counterweights and they were balanced for the HO pistons, so yes the HO crank is a different part# but I don't know if the crank throw's are the same or not between the HO and non HO.
 
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