map sensor questions

okay my fuel milage REALY SUCKS bad,i have a 88 with renix, alot worse than it did before i did my motor swap to the 93 ho motor. 2 days ago i drove about 100 miles and it took close to 3/4 of a tank. this is rediculus. i can kind of afford it right now but soon as school starts and im not getting a pay check anymore is when im gonna run into the serious problems. its running very rich and i just replaced the 02 sensor about 200 miles ago, its also idling very rough too, which sounds alot like some of the the other threads said was there map sensor either broke or the line broke. so i just went out and looked to see if the line was broke and i realized im an idiot and dont realy know what in the world a map sensor looks like. but i knew the line was a small hard line that came off the throttle body. well i was in luck cause there is only one. it goes towards the back of the jeep to about the end of the intake manifold, then pulls to 90 degree angles then come back past the throttle body and to some small port/sensor looking thing build into top of the intake manifold. so im guessing this is my map sensor? sorry for being so dumb. so is there any test i can do to see if it is my map sensor? and if i need a new one about how much $$ should i plan on having to put down for one? once again im sorry for being such an idiot and all but hey at least i searched first and couldnt find much.

kolby

Yes, that is the MAP sensor. Not sure how much a replacement costs. You can check the web prices from autozone.com or cskauto.com.

The MAP sensor is on the firewall, just to the right of an imaginary line drawn over the valve cover as you look at it from the radiator. It has a flat plate on top and a 3 wire connector plugging into the bottom of it, along with a vacuum line.

If you back-probe the lines, one is ground, one should be 5v, and the other 0.5 to 1.8v at idle and 3.9 to 4.8v wide open (you can disconnect the vacuum for that one). That's from the RENIX manual. Check that the hose has vacuum to it too.

I'd not run it much that way, even if you can afford it now. It'll potentially ruin your O2 sensor and cat, as well as foul the plugs...

Let me know if the description above doesn't cut it...

Just a thought - you say you swapped in a 1993 engine and the location you describe for the sensor is where it would have been mounted on the '93, right on the manifold. As others said, the Renix system's MAP sensor is mounted on a little bracket high up on the firewall, just to the driver's side of center. Besides the change in location, is there a possibility the sensor itself is different and delivers different values than the Renix ECU expects? The sensor used on the Renix came from GM, not ChryCo. All of them I have seen look similar, but who knows?

For a replacement your looking at 45-50 bucks. Check all the small diameter plastic tubes and make sure one is not cracked or broke. This will cause all of your issues that you have listed and I would beat that the MAP sensor is bad.

Dave in Eugene said:

Just a thought - you say you swapped in a 1993 engine and the location you describe for the sensor is where it would have been mounted on the '93, right on the manifold. As others said, the Renix system's MAP sensor is mounted on a little bracket high up on the firewall, just to the driver's side of center. Besides the change in location, is there a possibility the sensor itself is different and delivers different values than the Renix ECU expects? The sensor used on the Renix came from GM, not ChryCo. All of them I have seen look similar, but who knows?

Click to expand...

i think we can rule that pretty well out because i reused the 88 intake manifold, all my old sensors, all my old accesorrys including water pump, my old oil pan, pretty much all i used from the 93 was the short block and head, i did not use a single sensor from the 93. ill go out and see if that description is good enuf for me tofind it.

kolby

Just to clarify, the map sensor on the Renix and Chrysler versions, at least through my 95, is the same sensor, and approximately the same location. That line should go straight from the throttle body to the sensor on the firewall. Note that the Renix throttle body has two holes in it, one blind. The original map sensor line has a double-titted rubber fitting to match it; make sure that it is not in upside-down. The Chrysler version taps off the manifold rather than the throttle body, but it still goes to the same sensor. So if the lines are as described in the first post, there's definitely a problem with routing.

okay i went out to my jeep and found the map just fine with the description above. and it had the three wires attached but NO vaccum line, so i pluged the line on it and then didnt know where the other line went that was origninaly conected to the map vac line(it comes from a port on the top, front part of the intake manifold) so i laid it where the bends in the hose didnt have any preasure on them, and it was right by a rubber grommet type deal on the tappa cover, and it had a hole the right size in it so i plugged it in there and everything seems to be working GREAT, it runs quite a bit better and best of all there is no more rough idle and it doesnt blow any more black smoke you guys are all awesome. thanks a million.

kolby

alright i drove to my girlfriends,church, and to lunch and back (about 50 miles total)and i only used about 1/8 of a tank!!!!!!!!!! to say the least im pretty happy. my only remaining question is when i start it up now it revs to about 2700 rpm then slowly drops back down. it didnt do this before i plugged the map sensor vac line in. is this normal? if its not what could be my problem?

kolby

What do you mean by "plugged?" To me, that means blocked. As an earlier message stated, the VLine goes between the MAP and the base of the Throttle Body. It is a measured orfice size. If you used something else, you should get one from the Stealership.

Make sure you do not have a vacuum leak, which high idle often is a symtom of.

Did you replace your O2 sensor?

sorry on my word usage, i didnt mean plugged like blocking, i should have said connected, as of put the vac line on its proper thing(round thing u push it on, i have no clue what u would call it.) and yes i did replace my o2 sensor about 2 weeks ago, but one of those 2 weeks i was on vacation so it didnt get driven any.

kolby

It's been a while since I had a Renix XJ in full view, but I'm pretty sure you've got the right line going to the valve cover now.

For the revving, you might still want to check for other vacuum problems, because it' sounds as if there may be some unresolved issues there. Also check and clean all your electrical connections, and make sure the idle air controller isn't carboned up. And do make sure you are using the correct line and fitting for the MAP sensor and that the double-titted plug at the throttle body end is not upside down (i.e. check that the vacuum line is connected to the hole that actually goes through the throttle body, not the blind one).

ya im 99% sure the map is hooked up right now because when i did just that it made a HUGE diffence in how it ran and what milage i get. i said that it revs to about 2700 right after i start it then comes right back down to normal, but i noticed that it does not do this when its cold, but if its already warm it will do it.

kolby