Hey guys. I'm a marine technician so I know a thing or two, but I need your Ford expert advice......

I was having some issues recently. I suspected MAP so I began to test. My understanding is that Ford used 2 types of MAP- voltage varying and frequency varying. First time I have seen that.

Question 1: What years had which?

So, my tests- 5v reference ok, ground ok. Key on engine off signal wire reads 2.52v. Should read 5v. I apply 15 in hg vacuum to sensor- no change. I start truck- no change. Thinking MAP bad. Had a spare MAP from junkyard years ago, put it on. Did same test. SAME readings. Made me think there was more to this. So I thought maybe I got the frequency varying type. I put inductive tach leads on sig wire and ground. NO READING key on or engine running out of both sensors. Tried to read Hz with DMM. Reads 0. Strangely AC voltage reading about 2.72 (if memory serves right). Something is way strange with this. 2 MAP sensors are not going to fail at the exact same voltage to me.

I believe I have the voltage varying type but maybe I am running wrong type sensor?

I look on rock auto and the MAP they have says 87-96 (motocraft). Haynes says voltage varying type was early model and freq. type was late model.

A side note- I have been through 2 MAP sensors in 2 years with this truck which failed and threw codes. I replaced the first with the cheapest autozone one then had one from boneyard i pulled years ago and stuck it on. No codes.

Any suggestions???

 

Found a source online that confirmed the manual incorrect and that key on engine off reading should be 2.5v. I checked frequency with tach set to 6cyl, 4 cycle. Cannot get reading.

 

I assume you are back probing the wires. On that assumption my first suspect would be the connection in the coupler. Its common when the wires have been proved several times. Clean it up and check the connectors for flaring on the female side and damage on the male then test for wire integrity. Finally just to be sure backprobe both sides for a continuity check. At the moment that's the only thing I can think of that would give you a fail 2x on a bench test, short of 2 bad units or bad testing procedure. The sensors aren't really prone to failure obviously. BTW a map failure usually will throw a code. Have you checked and did you receive any codes? Finally what year and engine are we talking?

Oh you did test ground right?

 

Hey Warlockk thanks for the response. I am not back probing I made a breakout harness from a piece of old engine harness that had a MAP connector on it. I have verified ground as good. I usually check wiring before sensors by verifying 5v reference to good known ground then checking the 5v reference to sensor ground. Ground was ok. Connections were good. No codes, I have had 2 MAPs set codes before and were bad. These have set codes, but not always as you know a sensor will not set a code unless it fails out of range.

My understanding is that late models used the frequency type sensor. My tach did not read anything when set on 6cyl 4 cycles. I probed signal wire and ground.

My truck is a 1993 f150 302 5.0 v8 e4od tranny. I appreciate your help man.

Overall my guess is that the sensor is good. I am trying to track down a problem on cold start. The engine will bog and sputter until it finishes searching for rpm then will shoot to 1500 and do its normal warm up and bring it back down. Sometimes it surges. If I let it search and it catches itself it will run fine. If I shut it off while it is doing this it will not restart unless I open throttle when restart. This tells me its probably flooding. Something is causing it to dump excess fuel at cold start. I have already replaced IAC. I am focusing on coolant temp, MAP, TPS. That's kind of the deal right now.

 

On one of my vehicles, faulty coolant temp caused the same symptoms.

 

^ that's my first thought on a cold start assuming IAC is OK. Have you checked IAC for proper function. Making sure it opens properly. If not that would definitely cause flooding. Another thought is fuel control circuit or return line restriction. Also leaky injectors. Its a tough symptom to track. If you have access it might be a good idea to look up a diagnostic flow chart on all data or something similar to help organize your hunt. I don't have access to fords tech sight since I finished the training course. I always loved their logical flow charts. Keep us posted and I'll thou out ideas as they come.
Edit. Oh weak spark or bad base timing would be another cause of hard start/ flooding. Easy to test.