I am doing a MAF conversion on my wife's 1994 F150. However, it gets a bit complicated in that I am also swapping from the factory 300 to a 351. While the 351 is used (298K miles) from a truck I retired a couple of years ago (still running at the time), I inspected the block; both top & bottom; finding there to be virtually no carbon buildup or signs of wear. I installed freshly rebuilt heads, replaced the oil pump as well as the timing chain & sprockets and the distributor, spark plugs, and wires. Cold compression in four cylinders is 160 PSI, two at 150 PSI, and two at 135 PSI. Oil pressure (while manually priming system) is 65 PSI. The truck also has a manual transmission and is 4WD (after a conversion from 2WD a couple of years ago). Everything is all together with the entire underhood harness swapped to one from a '94 F150 and a Cardone rebuilt HOG0 PCM. Fuel pressure is good (~40 PSI). All injectors have just been rebuilt by Injector RX with the test sheet showing all injectors flowing just under 21 lb/hr.with good spray patterns. Timing while cranking is set close to 10degrees BTDC. All wires underhood have been traced with continuity verified using a Rotunda PCM breakout box. The only test out of range is with the MAF sensor showing 6.5 instead of 12 volts. I have a new one ordered that should be here soon. Engine OBD1 codes (KOEO) cold, of course, are 118 "ECT sensor above maximum voltage / 0 to -40 degrees F" and 637, 654, 621, 622, 652, 624 which are all auto transmission related. The engine fails to fire at all - even when hit with a small shot of starting fluid. Is it possible the MAF sensor issue is causing the failure to even fire? Or, is it possible one or more of the 600 series (AT related) codes is/are the problem? I have read reports from others who have used AT PCMs and tricked the PCM into simply seeing the transmission as always being in N or P. Any thoughts are welcome, but most appreciated would be guidance from any who have successfully completed any part of what I am attempting here.

 

Someone correct me if I’m wrong but the computer sends out a 5 volt reference signal to the sensors so if you are getting 12 volts to the them then that is a problem. If you cycle the key a couple times what is the fuel pressure? It sounds like you don’t have ignition so where are you losing spark?

 

MAF is fed 12 VDC from the PCM Power relay load side contacts. We need to know how/where the OP is measuring that 12 volt signal.

 

I am getting 12 volts to the PCM (circuit 361, pin 37). It just occurred to me I cannot remember if I am getting the reference voltage (circuit 351, pin 26) so I will reconnect the breakout box & test that again. Each of the injector wires do have 12 volts on the red wire (circuit 361) and I am getting the timing light to trigger while cranking; which is how I got the timing close to 10 degrees BTDC.

 

Power ground for the MAF goes to ground G101. The MAF Return goes to PCM Pin 9. If you are getting the full 12 VDC to the MAF via the PCM Power relay/Splice S136, I assume your 6.5 VDC reading is the actual MAF signal output going to PCM Pin 50. If that is the case you most likely have a bad Signal Return circuit, open or high resistance, going to PCM Pin 9

 

You've sprayed with starting fluid and not even a hit? That could very well be an ignition issue.

You can put a timing light on it and crank it to see if it flashes while it's cranking.

 

Agreed on the no fire with fluid. Yes, as I wrote, the timing light does light, with timing now set to 10 BTDC. The new MAF sensor appears to make no difference. I am positive of my crank & cam alignment; especially because before I installed the engine I realized I had not torqued the cam sprocket bolt to spec so had to take the front cover back off to do so. Thank you for your thoughts.

 

Did you have the distributor out? If so it's possible you have it 180deg off now.

 

Agreed with the others, the timing is probably 180 out. An open MAF return is not causing the no start issue, but will cause driveability issues once the engine fires off.

 

Update: Indeed, I had inadvertently installed the distributor 180 degrees off. Now, on to resolving other issues - like why the engine will not idle down after warm up and why I now have no tach function. And, verifying the the CEL is on simply due to using an AT PCM with a MT or if I now have other codes. Thank you all for your help!

 

With an AT ECU and MT gearbox, you need to trick the ECU into thinking it's in Neutral.

You can reconnect the MLPS, and place it in the neutral position. Then, just tie it all up and out of the way.

Or, if you have a diagram, you can insert a jumper wire into the connector to simulate an N condition, and that should work as well.

 

There are some functions of a MT PCM that wont be present tho, like the situation when you press the clutch pedal at, say, speed, the way the idle is lowered and put to the proper RPM ,as well as what happens if you were to release the clutch , I dont know how much of a difference this would be, but there is also the standard idle is lower on a manual than an auto And some timing stuff I think

 

And, probably related to a variation in pin locations in a connector or two, is that I also have no tachometer function. I will be tracing those as well now.

 

With the databases I have used for tuning, and if my memory serves me correct, 704 is the setpoint RPM at idle. Now, I have not seen every cal code database, so there may be differences. One thing I will point out is that mass air databases utilize a transfer function for the IAC valve, whereas the speed density ECU's use a simple function table. This makes a difference in the way the idle responds to tip-in & tip-out conditions. If there are differences between the two, I believe they're minimal and not something that will cause the motor to misbehave.

 

i also heard of hanging revs when clutching, but ive only heard that from the people on EECtuning so its possible its not a common thing too, but good points, thanks for the info , adds a good bit to the discussion