Oh Yeah, he said to put a tee between the map and the vacuum line and get avac. pump and pull a vac. while engine is running and it will clear the problem, and if it does that confirms his bad news....ever heard of that trick ??

 

Are you saying that if you put a hand pump a vacuum on the MAP sensor and the miss goes away it confirms that the engine is worn?
No I have not heard that one.

The MAP sensor tells the computer what the difference is between the engine vacuum and the outside atmospheric air pressure. The computer uses this information to set the fuel air ratio from a look up table in its program.

I think he is trying to say a worn engine will not have as much vacuum and the engine is missing because of the fuel air ratio is wrong. By putting vacuum on the map sensor you will correct the air fuel ratio and the miss will stop.

OR you could just use a vacuum gauge and a compression gauge to see what the engines condition is.

 

I can only assume that's what he meant, sounds good anyway. Well I changed out the IAT and the ECT and still have a mis ....,oxy sensor is next or I'll just meter it.
The IAT had oil all over the tip and looked like it had been there awhile and didn't ohm out like it should have. I even disconnected the Neg. on the battery trying to reset but that didn't help either....If I can't get this I'll no choice but to take it to a garage for repair...Man I hate to do that..

I don't have any gauges that would tell me vac. or pressure and I'm curious about the fuel pump or filter, would or could that cause a slight mis ?

 

A lot of the auto part stores will loan (rent) you the gauges and other items.
If you do not want to buy them this may be a route to take.
You could also have a bad spark plug even if it is new.
I pressure test spark plugs to see when they quit sparking, sometimes I use one or two of the old plugs with the new set if they test better.

 

I have a 1994 E250 w/5.8L that may have a similiar problem. A year ago it started surging and dying at idle. I would have to put it in neutral to keep it running. It also surged/missed at lower speeds through town. It then developed pinging/missing under medium acceleration and started banging and missing when the torque converter was locked up at speeds above 30 mph. It was recommended I flush the transmission, which I did. No change. I changed the EGR valve and sensor that sits on top of the valve, replaced the idle air control valve, replaced the throttle position sensor and cleaned deposits from the throttle body. No improvement. I was told that my transmission was way beyond the normal life (250,000 miles) so I replaced it with a Ford remanufactured unit and torque converter. All of the driveability problems went away. But, I could no longer start in neutral and the transmission banged into gear. I had to rewire the transmission connector during installation and had miswired. The computer wasn't talking to the PCM. I rewired, the transmission shifts perfectly and starts in park now. However all of the driveability issues have returned. I forgot to mention that I also replaced the plugs, cap, rotor, fuel pump and fuel filter. The differential speed sensor had been replaced prior to these problems. I have suspected the coil, the MAP sensor and wires, but decided that the van wouldn't have run perfectly after installing the transmission if these things were bad. I am now suspecting the PCM but don't want to spend another $400.00 in case I'm wrong. A local shop says there may be a bad sensor, wire, ground or who knows what that may be causing the problem. The question is, what is involved now that wasn't involved when the transmission wasn't communicating with the PCM, that is causing these problems? Supposedly there is a speed sensor in the transmission that sends signals to the PCM, maybe the PCM isn't processing them properly?

Gary

 

I had people about the replacing that as it DOES control just about everything, last resort until I figure out this problem and exhaust all other cheaper ave.

 

The PCM does control everything, but why should the driveability problems arise only when the transmission is in the picture? What year and mileage is your van? Does my problem sound the same as yours?

Gary

 

I have a E350 7.5 gas (460) 134,500/

It sounds somewhat similar, If I run it a any steady given rpm it starts to have a intermittent mis , but it does it does not do it when I accelerate it.

Transmission shifts fine, I've replaced IAT and the ECT and may go on to the oxy sensor, I replaced all the plugs and plug wires, rotor,cap, I also ran injector cleaner....a lot they don't seem to be failing, it also burns rich when it misses...hhhmmm that may be a clue, well now I've also replaced the MAP due to it coded and cleared after replacing. So no I don't think we have the same problem as mine will do this at any speed.

 

What is IAT and ECT? Mine also misses intermittently at most any speed. It almost never misses at full throttle. I didn't mention that I also replaced the oxygen sensor. Ford seems to be making a lot of money off of our problem.

Gary

 

Intake air temp. sensor, engine coolant temp. In conjunction with the oxy. sensor they give the ecc info re: ambient air temp and coolant temp and with oxy determine if it's burning rich or lean, this as far as I've got reading up on this stuff, the first two items and the third work together to change timing and fuel/air ratio..

 

Check the vacuum hose at the FPR. It there is fuel in the hose replace the FPR.
Make sure the MAP sensor vacuum hose is OK. Low vacuum at the MAP sensor will cause rich mixture.
Check the TPS with a analog VOM to see if it sweeps smoothly across the scale from 0.9V to 4.5V.

 

In regards to my van, wouldn't you think if any of these things were wrong that the van wouldn't run correctly wether or not the transmission was communicating with the PCM or not?

Gary

 

Gary: I'm not sure at all, I have VERY little exp. working on late models, learning in doing it,.
Subford: My brother mentioned that TPS as he had a problem a while back and that took care of it. So that is also going to be looked at tomorrow mourning. thanks for reminding me and giving me the voltages. What is the FPR ?

When I original pulled all of the codes TPS and Map came up as well as a trans "switch plate" ? any way replacing the map cleared all of those codes so...?

 

The FPR is the Fuel Pressure Regulator.

 

Oh ok, the vacuum line is on the top isn't it ? and does that come off the fuel rail ? easily ....I was looking at that today while I was changing the IAT....man was that chore.. not much room in there working on a van. I hope it pays off in the end.