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Possible bad map sensor

1K views 15 replies 4 participants last post by  07gtS197 
#1 ·
So its not a mustang but it does have a 5.0. My 85 crown vic is having some idle issues. Ive fixed most of the issues but now Ill have a rolling idle that sometimes will settle if I rev it. The idle will sometimes drop or raise out of nowhere and run rich. It will wreak of gas from the exhaust and around the cfi (its a cfi by the way lol). And a new symptom has appeared. Last friday I went to a car meet and all was well but after sitting for about 20 mins it acted like the battery was dead. I had a buddy jump me and it started right up and its been starting fine ever since. I ran it today in my driveway for half an hour to see if it was the tfi and after turning it off and it would crank longer and slower. Im throwing codes 22 and 44 so Im on the fence about the tfi module going out but can all of this be caused by the map sensor?

Sorry for the long post but Id like to get this car squared away.
 
#2 ·
I bought a new map sensor and will install it and report back afterwards. Anyone have any problems with their map sensor? I cleaned out the connector on the map sensor and voltage regulator and it seemed to start up quicker but I wont know for sure until I get the new map sensor and test again.
 
#3 ·
I had similar symptoms with my IC (ignition control module) on my 92 5.0 f150. When shifting from drive to park after coming to a stop, the idle would surge up and down, try to die, then steady out. I also noticed an extended crank (but not slower) and I had a misfire in 3rd and 4th gear and low vehicle speed and low engine rpm (high load condition) when the torque converter clutch was engaged. It shook the whole truck really bad, but at higher engine rpm no misfire. I ended up going down a huge rabbit trail replacing the entire ignition system before I found out it was the ICM. I've since put 3 parts store ICMs on the truck because they keep failing. Truck will run great for a month, then I'll notice an extended crank and surging idle, then one day it'll just die like you turn the ignition off. No stumble or backfires, just off. I'm beginning to wonder if I have a short in the wiring causing the failure.

Not sure if this helps. I don't know of an effective way to test the ICM for proper operation.
 
#4 ·
I appreciate you responding and its looking like either the tps or icm. I tested my tps a while back which tested fine, .98v closed, 4.8v at wot and smoothly increased with the throttle plate opening. I rechecked later while it was running and it was at 1.07v at idle and it would surge but the tps voltage didnt move so Im not so sure thats what the problem is.
 
#6 ·
Cfi's dont use iac's I wish it did so I can get a new one and pitch the old one lol. Im eventually going to swap it to efi and be done with all of this cfi nonsense but I dont have the money right now. Anyway, I unplugged the o2 sensor on a hunch and sure enough it ran better than before, except it still runs hot and chugs in 3rd but it doesnt surge or idle funny. Now the question is, is it really the o2 sensor thats causing my issue or are my problems caused by something else and the o2 sensor trying to compensate for it? Im hopeful its a bad o2 sensor but I guess it could be bypassed by running the car in open loop. It looks like Ill have to just buy a new one and see if it fixes my problem. Thanks for responding!
 
#7 ·
A vacuum leak will cause surging & a rich fuel mixture because the O2 sensor reads the extra oxygen in the exhaust,setting a lean code then the computer tries to compensate by (falsely) richening the fuel mixture.You can let the engine idle while running a hose(attached to a propane torch with the gas valve open)alongside any suspect leak area.The leak will draw propane into it & that'll cause the idle to increase temporarily, indicating youve located the leak.Good places to check are the cfi unit gasket & any other gasket,vacuum hoses & fittings & any vacuum operated components.
 
#8 ·
Ah just who I wish would answer, the sbf textbook himself lol. So far the only leaks Ive found are one of the hard plastic lines going to the purge valve (which Im throwing a continuous code for) and pcv but theyve been taken care of. I was starting to think maybe the throttle body to intake manifold gasket but I dont have a propane torch so I cant test it precisely enough.

And to clearify this surge Im talking about, its more like the car will rev maybe 100 or so rpms but I have no tach to verify what rpm its climbing to. And it only does it after its warm, which leads me to believe its an egr issue. I dont know if I updated this thread but I unplugged the o2 sensor and went for a cruise down the street to get the issue to return but it did not. It will run better with the o2 sensor but do you think its the o2 sensor itself going bad or because its running in open loop all the time its bypassing the real issue?

Oops it looks like I did already post about the o2 sensor.

Another symptom, before I forget, I just noticed a couple of days ago if I smack the throttle quickly itll cut out a bit and a puff of smoke will come out the back. Im pretty sure its black smoke but it dissipates so quickly. It seems to me like something is slow to respond to throttle input.
 
#9 ·
I was starting to think maybe the throttle body to intake manifold gasket but I dont have a propane torch so I cant test it precisely enough.
You can use carb cleaner too,but it can get a lil messy.Do it on a cold engine if possible.
 
#11 ·
No vac leaks found but I managed to swap out the map sensor and take it for a spin before it started pouring again. It seems to have smoothed out the idle and it doesnt chug when its low in 3rd anymore so I think Ive solved my problem. The only other big issue now is its hard to start and slow to start (sometimes it wont and act like the battery is dead) when its hot. When its cold it cranks strong but will crank excessively before it fires up. When its hot it cranks slower and will take longer to start. The last time I took it out for an extended drive (20 or so miles) it drove fine but when I went to fire her up again it acted as though my battery was dead. It cranked really slowly and got slower. My buddy drove over and literally after 10 seconds of it being jumped it started right up and has been fine ever since. Im guessing either my starter is going or its an ignition component.
 
#12 · (Edited)
The first thing I would do is inspect your grounds.I had a "slow crank when hot" issue that turned out to be caused by 4" of insulation rubbed off my starter cable at the oil pan.The cable had been resting against the corner of the oil pan & it wore the insulation down to a bare wire,which was causing excessive resistance in the circuit.Be sure to check all grounds from one end to the other.If you run your hand over the entire length of the cable,squeezing as you go along,a soft spot will indicate a possible break in the cable.
BTW-if your starter cable has a loose or corroded connection,internal break or bare wire touching metal,excessive resistance will occur & heat will also add more resistance.Disable the ignition,touch the leads,of a voltmeter,to the (+) & (-) battery posts then crank the engine.Battery voltage should be above 9.6 volts during cranking.If not,the battery doesnt have enough reserve capacity to start the car.
One thing that can help with the slow cranking condition when hot is to upgrade your grounds.The link shown below will detail whats needed.I know youve got cfi & not efi,so just ignore the eec ground upgrade thats listed,unless of course the cfi computer uses a ground,similar to the eec ground.
How Important are Grounds in a Ford

Its also possible that the starter could be developing heat soak issues,due to the proximity to the headers.If this is the case,a starter heat blanket will help or header wrap can also be used.Another option is to grab a high torque mini starter from any
92-95 Mustang 5.0
94-04 Mustang 3.8
92-96 Bronco
92-02 E Series
92-98 F Series
90-91 Crown Vic
90 SC Tbird 3.8
91-97 Tbird 3.8
91-93 Tbird 5.0
 
#13 ·
Thanks bro Ill check all that as soon as the weather clears up. Its tough enough having to work on all of my cars on pavement but its worse when theres no shelter lol.

Supposedly the po replaced the starter so Ill pass that for now but keep in mind. These cars are known to have the high pressure power steering line rupture, which looks like it happened some time ago on mine, so theres a lot of cleaning to do. Im betting the dizzy is oem and so is the ignition module so Ill swap at least the ignition module when I can. The positive battery terminal and starter solenoid are newer so Im not going to touch them yet. Its looking more and more like the timing (Ill need to recheck), ignition module, coil or maybe even fuel components.

A few days ago I noticed a sould like a glub glub glub coming from the engine bay and found out its coming from the air pump check valve so it looks like I have another vacuum leak. I recently pulled the air pump (the po removed the pulley and crimped off the end that goes to the cats, no cats btw) to completely delete it but Ive been busy and bad weather has kept me from removing the tubes from the back of the heads. Ill update as soon as I can square all this away and test the grounds and battery.
 
#14 ·
As always thank you wbrockstar. I finally got a chance to check everything. I have a few problems that are all contributing to my slow start when hot and hard starting problem. It seems that I have a vacuum leak at my smog pump check valve and I dont have a smog pump, Im assuming my fuel pumps are getting weak and my ignition control module (mines attached to the distributor) is getting heat soaked.

I checked my grounds and all are good, they even still have their wiring looms on still. I think most of them have been replaced. The ground from the battery to the block is soaked in oil but thats it. Oh and my eec ground is attached to the battery.

My battery voltage while cranking stayed at about 10.5 volts and the voltage when off is around 12.5 volts. I did notice after I reattached the ignition and cranked it it almost started immediately. Im thinking the fuel pumps are getting weak and/or the spark is weak. Ive tried cycling the key on and off up to 4 times before but it made no difference in starting. I do notice it will tap a little on startup then go away afterwards but maybe its pinging due to not getting enough fuel after the fuel pump primes because its bleeding off quickly. What do you think?
 
#15 ·
I checked my grounds and all are good, they even still have their wiring looms on still. I think most of them have been replaced. The ground from the battery to the block is soaked in oil but thats it. Oh and my eec ground is attached to the battery.
Remove and clean all your grounds until they are nice and shiny, even they look ok. An oil soaked ground can hurt performance. Cleaning the oil soaked grounds on my Jeep made a huge difference in overall driveability, and got rid of a couple trouble codes in the process. It was well worth it.

And if you need to find vacuum leaks, try this.



Forget the glass and just buy an empty metal paint can from Home Depot or something. They are much much easier to drill, and wont shatter when you drop it.
 
#16 ·
I measured the resistance from the battery to a few places and they were all within .5 or less ohms. Its been raining so I havent been able to check resistance at the starter but Ill check that. Like I said the little purge canister plastic hoses are split and need to be replaced so thats one spot. The check valve for the smog pump is another I think and Im not sure if my fuel pump is keeping the proper pressure. I dont have a fuel rail pressure gauge and autozone didnt have any so I put a small screwdriver in the schrader valve at the rail to check for pressure and it did but didnt shoot out like I expected. Ill see if I can get one today to rule that out. Im thinking maybe my coil is on its way out and is weak. I pulled the coil wire and had my mom crank the motor for about 5 or more seconds to check battery voltage like brock said. Then afterwards I tried starting it with the coil plugged in and it started quicker than usual but not as quick as it should so Im thinking it has weak spark. It shouldve dumped plenty oil fuel to start after one or two cranks but it was still a few more cranks.

Ive seen a few vids on youtube of these cars and they all start fairly easily and quickly. Ill try to tackle the fuel filter and get a fuel pressure tester tomorrow. And Ill clean at least that block ground.
 
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