Need Help

Topic: Need Help (Read 752 times) previous topic - next topic

Need Help

August 09, 2006, 10:53:18 PM

I just recently put a 5.0L HO out of a mustang into my 88 cougar (was a 5.0L 155 horse). My car has a rough idle to it and seems kind of slow of the start but one you get it going it goes good. I was reading this off the coolcat website:
MAP Sensor / COST: ~$60
The MAP sensor hangs on the firewall, just above and to the right of the upper intake plenum (just to the left of the wiper motor). This reads the Manifold Absolute Pressure, and since you'll have a different amount of vacuum with the new camshaft, you must also replace this with the '87-'88 Mustang 5.0 variety. If you experience rough idle, bad starts, no starts, or general bad behavior from the engine, immediately replace this sensor. In talking with several others that have performed the HO conversion, it's been found that the MAP sensor makes a world of difference and therefore is MANDATORY for the conversion. Now there are tons of part numbers for this sensor. If you visit the local auto parts store, they'll generally list two sets of part numbers----one set (about 15 part numbers) for the cheaper MAP sensor, and one set (2 or 3) numbers for the more expensive sensor----guess which one works!! Mine is E7DF-9F479-A2A, and it worked fine. Incidentally, the 1989-up mass-air Mustangs have a BPS (Barometric Pressure Sensor) that is identical to the MAP sensor, save for the vacuum line. If you're ever going to switch over to mass air, you can use this existing sensor by simply capping the vacuum line and letting the MAP sensor open to the atmosphere
I just have the map sensor that was on my cougar before. Does this mean that i should buy one for a mustang?

Need Help

Reply #1 – August 10, 2006, 10:06:52 AM

Reg, you may have another issue going on here. Is the IAC (bypass valve) clean? Is the EGR/EVP system working properly? Are the O2 sensors good, and clean? How about the timing...are you at 10 degrees? Have you scanned the computer for codes yet?

There are a lot of things that affect idle quality and the MAP sensor is second-to-last thing to change (last being the computer itself). Hell, I've even seen a borderline faulty TFI module affect idle. Give us some feedback here, let us know what you've checked.

Need Help

Reply #2 – August 10, 2006, 12:40:30 PM

I dont know how to check all that stuff. I did notice that one of the O2 sensors had a hole in the side of it. I was planning on replacing them. I dont know much about cars, I have a friend that does most of the work. How do i go about checking the IAC (bypass valve) and the EGR/EVP system. I bought the mass air kit from IST, so the computer and mass air stuff is new. I just read the thing about the map sensor on the coolcat site and figured that might be my problem cause it sounded like what my car was doing. Since i use the map sensor and egr/evg sensor that were on my old non ho motor i thought, i might have to get them for the 5.0L HO mustang motor. Iam confused please help. I was told by a local mustang owner that everyone with a mustang around here takes off their pollution pump. So i took all that stuff off and plug the hoses that were going to them.

Need Help

Reply #3 – August 13, 2006, 10:30:34 AM

If your EGR was good before, it should be okay now. Most of the stuff from the Mustang motor would be almost identical to your stock sensors anyway.

O2 sensor with a hole, you say...hmmm...that could do it. Try unplugging that sensor when the car is cold, then start it up. If it idles better then you found your problem.

The EVP is attached to the EGR valve (it's what the wiring harness plugs into). You can remove the EGR and clean it out with some carb/choke cleaner. Also, the IAC (bypass valve) is on the front of the throttle body. Again, that can be cleaned out. Also you can clean out the throttle body itself. Basically any place there's carbon buildup there's also the chance of causing a rough idle situation.

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Reply #4 – August 15, 2006, 05:14:26 PM

I might of missed something here,but do you have ho computer in it?