ok i have a 91 F150 302 efi. last week the truck ran like a champ. this week no such luck. like a light switch something went wrong and i think its sensor related. when i run a vacuum test the needle runs in the red late timing area. last week the vacuum was perfect now its running at 14 on the vacuum gauge. it also surges i checked all the ignition that was all good has new wires and coil. now this is interesting because when you go wide open from idle it back fires through the intake making me think the timing is off. i know the vacuum affects the timing. now here's the interesting part if i unplug the vacuum hose from the MAP sensor the engine surges but the vacuum stabilizes and runs at the normal 25 range on the vacuum gauge and it idles smooth but the truck violently jerks forward when you put it in gear and when it shifts (automatic trans) and when you back off the throttle it acts like it wants to stall. i plug the hose back the vacuum drops to 14 or worse. is the hose is disconnected the check engine light comes on if its reconnected it turns off. so I'm thinking i have one of the two problems my MAP sensor bit crap or my egr is stuck because it makes so weird noise when you rev the engine. so whats going on here? is this sensor related? I'm cant find any vacuum leaks or intake manifold leaks anywhere.

 

hmm my gut instinct would be you've gotta bad Map sensor if engine vacuum goes to normal with the Map disconnected but assumptions are dangerous for the Pocket Book when it comes to EFI...So I'd suggest getting an Code Reader
in particular a Equus 3145 from Oreilly's for $29.99+tax if applicable in your state

just out of curiousity though whats this strange noise, and is it specifically coming from the EGR valve it'self???

 

it sounds like weird like spring click or something. it sounds like its coming form the egr i could be wrong. should i clean it? can the egr cause the MAP to get bent outta shape? btw it did rain extremely hard and the MAP sensor is right where moisture can get in so could the rain cause it to short or something?

 

oh and also if i pull the vacuum hose on egr and put my thumb on it as i rev the engine there's no suction so do i need a new egr solenoid?

 

hmm. you should get vacuum with increased RPM from the solenoid I'd think. but like I said I'd get a Code Reader it's been a god send with my 90 it's told me of 4 defective sensors EGR Valve Vacuum control solenoid and the EGR valve position sensor aswell as the O2 and Knock sensors I'd have never figured all that out without it. you could try cleaning the EGR valve but becareful with the tube when removing it that you don't bend or twist it outta shape. but no unless you had wires bare on the map sensor and crossing each other out the weather can't hurt the map sensor

EGR Valve electronics problems can cause alot of problems though but like I said though you won't regret getting one of those code pullers for these particular issues and issues you may run into in the future. the Solenoids relatively cheap though if you need it or just want to replace it

 

is there anything else that can affect the MAP sensor?

 

sorry to join the chorus of "pull the codes" but, it'll help. you can always do it the cheap way if you've got patience.

Ford Fuel Injection » How To Run a Self-Test