Interesting problem. My 87 2.5L still has the original MAP sensor. I changed all the other sensors when I restored the car because they were questionable...and the previous owner had damaged most of them such that he parked it for 11 years. He was out of his element on fuel injected cars in my opinion.
It doesn't throw any codes with the original MAP sensor but the engine has a slight misfire at idle when the engine is at full temperature and a tiny bit of misfire when revving in neutral without a load but seems to accelerate and drive great. This just started a few months ago after idling fine for over a year. After much testing and diagnosis I determined the MAP must be at fault. Disconnecting the MAP makes the misfires stop which confirmed to me that was the cause. It definitely isn't ignition or compression related.
The "interesting problem" is that I bought a cheap, China-made knockoff MAP sensor from Amazon to try. That sensor fixed the misfire yet it causes DTC 45 (rich) intermittently when stopped at lights. Accelerating away from the stoplight works great and the SES turns off. Next time at a long stoplight the DTC 45 may reoccur, usually about half the time and it sometimes smells rich as well. So the new sensor fixes one problem only to cause another. That's what usually happens when I cheap out on parts
So thinking the cheap sensor is the problem I bought the AC-Delco version of the MAP sensor. Naturally, the AC-Delco part is ALSO a China-made part. Here's where it gets even MORE interesting. Installing that sensor throws DTC 33 (MAP low) immediately! The engine runs terribly with it installed and is hard to start. Throws that code every time and tapping on the sensor causes the engine to rev up/down. Clearing the memory and starting over has the same result. Every time. The wiring in the car is fine so the AC-Delco sensor is at fault.
I cleared the memory each time I changed the sensors so the ECM would learn operation with the installed sensor. I'm just amazed that I get three different results with the three sensors. Each one works the same bad way it did before when I retest them. Amazing since I expect the two new ones have the same IC in them but that is just a guess.
I was only changing the MAP sensor because I found the slight misfire at idle annoying. The car runs great without any other issues. Currently, I have put the original MAP back and I'm living with the misfire until I solve this but it isn't stopping me from enjoying the ride.
My question now is who makes a reliable replacement MAP for the Iron Duke? I've ordered one made by Standard since their parts usually work OK but I'm curious if anyone else has seen this problem? All three of them read 4.7V at KOEO (and 542 feet above sea level) and my scanner shows the idle value to be approximately 0.6V on the original and 1.1V on the "rich running" one. I didn't bother to check on the AC-Delco MAP since just starting it up proves it is crap!
Experimenting with starting it up using the original MAP and then using a vacuum pump to "trick" it into idling shows that when the voltage is at 0.8 the misfire goes away and raising it above 1.3V will cause it to throw DTC 45 so this tells me the original MAP is just a little out of calibration probably due to age...just enough to annoy me.
If I'm the only one experiencing this then I may play with adding an external reference circuit to tune it into range if the Standard version doesn't work. I hate to keep buying sensors since I'm currently 0 for 2.
I would probably use AC Delco or Delphi brands but do not use the AC Delco Advantage line. That line is really cheap low quality stuff. I do not believe that many sensors are made here in the USA, in Canada or Europe. We are now at the mercy of the Communist Chinese
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
Kind of what I thought when I got the first replacement. I just couldn't resist the dirt cheap price and luckily I can still return it if I choose. The fact that it cleared up the misfire had me thrilled...until it didn't the very next day when it threw the DTC 45...
The AC-Delco one was marked as "OE" on the box and the "2131545" part number so I assume that is the Advantage line. Ironically, Amazon listed the "Gold" one part number 2133205 as "does not fit your Fiero" which I really doubted. Probably should have gone with that because I didn't trust their statement. Oh, well, if the Standard doesn't work that's my next option.
The only ones I find locally in stock are the Autozone brand so it has been simpler to order from Amazon these days. Plus they are uber expensive compared to Amazon but if they work...
I agree about the Communists. We should have never allowed that to happen but it is what it is now.
" Disconnecting the MAP makes the misfires stop which confirmed to me that was the cause."
Nope. That puts ECM in "limp mode" to maybe run the engine till get home.
Test MAP needs a "mityvac" hand pump w/ gauge. See my Cave, Sensors Quick Ref
"yet it causes DTC 45 (rich) intermittently when stopped at lights."
Nope. MAP won't cause this. But iffy MAT, the plug and/or wires to it can. See my Cave, DIS Ignition location, See my Cave, 700 TBI
Or can have problem w/ TBI. Any small leaks are bad. Common is Fuel regulator like to leak and only see when air cleaner is open or off when engine is running to keep fuel pump on. Or ALDL G gets power to run fuel pump. See my Cave, ALDL/ALCL
If that happens get TBI rebuild kit.
"the engine has a slight misfire at idle when the engine is at full temperature and a tiny bit of misfire when revving in neutral without a load but seems to accelerate and drive great."
Likely Isn't the MAP. iffy spark plugs, wires, or other problems w/ the ignition. DIS Hates some spark plugs.
If had problem trying to accelerate, can also be Iffy EGR valve or gasket.
clean/fix all grounds in engine bay. Just 1 iffy ground can cause many headache. Coat bolted/screwed ends w/ silicon or brake grease.
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
Once again, ogre has misunderstood the question. I asked "Who makes a good MAP", not "Give me diagnostic info for something I've already solved".
My question is valid because TWO BRAND NEW MAP SENSORS behave differently from my original sensor without changing anything else. That confirms that all three are obviously DIFFERENT when the two new ones should have been the SAME. I just wanted opinions on which brand(s) had some success for other people so I could eliminate buying a lot of sensors. The two I bought may have been flukes yet I'm suspicious of both brands now.
Instead, you waste my time.
OF COURSE DISCONNECTING THE MAP SENSOR PUTS THE ECM IN LIMP-HOME MODE! THAT IS THE POINT OF THE TEST, which is one of the things that GM RECOMMENDS in the FSM for idle problems! When the ECM detects the MAP is missing, it uses the TPS to detect load, the CTS, MAT and O2 sensors to adjust mixture and the crank sensor to adjust timing advance. This means that if an IGNITION COMPONENT were causing the misfire then it would STILL misfire. It doesn't and I checked all of that before I ever starting checking the MAP.
I don't need to "see your cave" to use a vacuum pump to test the MAP. I've been using a vacuum pump to test engines, including my two Fieros for decades and did so as part of my diagnosis. My pump is actually a Craftsman that I've had since 1973. I also own a Mityvac I received as a gift years ago so you can stop suggesting I used the wrong brand vacuum pump. I use them both all the time. I also used one of my pumps to verify MAP operation by starting the car with no vacuum on the MAP and then immediately applying vacuum while the TBI vacuum hose was sealed so I could alter the vacuum signal to the MAP while running so I could tell if changing the output of the MAP corrected the misfire, which it did. Also, I measured the voltage at the MAP and compared it to the voltage reported by the ECM and it is spot on with every small change I made in the vacuum level which proves the ADC in the ECM is also fine. The sensor changes; it is just that in my opinion the calibration is off. Period. I was able to confirm with repeatable experimentation that applying a vacuum that produces 0.8V to 1.2V from the MAP stopped the misfire and I let it idle that way for almost an hour without ever throwing a code. That's what convinced me to try a new sensor. I watched the spark waveforms on my engine scope and could see the misfires when they occur and when they cleared up based on the MAP signal. So I don't need your diagnostic help, thanks anyway. If I wanted that kind of help I would have asked for it but I didn't. I asked for suggestions on BRANDS of MAP sensors. I spent 35+ years designing and performing diagnostics of computer-based electrical and mechanical systems for a living so I got this. More than willing to help others, just not willing to tolerate your abusive behavior.
GM reports the MAP CAN CAUSE the engine to run rich at idle and they recommend substituting the MAP with a known good MAP to verify if it goes away. Sorry, I trust GM's credentials over yours. My problem was BUYING a KNOWN GOOD MAP sensor. I bought TWO that aren't good. By your logic, the MAP can't cause this; well, your logic is faulty since if my original sensor works DIFFERENTLY from the two new ones and the FIRST NEW ONE did cause rich running without making any other change. Therefore your statement is just plain false. If the original is "good" as you seem to think then why would two new ones not work the same? That should have proved you right if that was the case but instead it didn't because they are bad! Circular logic on your part. Bad scientific method on your part.
The MAT is perfect. Not only is it relatively new, after the engine sits overnight the ECM reports the CTS and MAT are within a degree of each other and are spot-on with my laser thermometer. I checked them several times on different days when the outside temperature was different and the sensors agreed with my thermometer and each other every single time. When the engine is at operating temperature, both the CTS and MAT were within a degree or two of my thermometer readings at the sensors as reported by the ECM. The MAT is fine. One of the reasons I checked it so thoroughly is that YOU are constantly blaming the MAT for everything bad, including athlete's foot. I took that to heart figured it was worth checking. I even replaced it with a resistance decade box to see if varying the resistance would have a drastic effect while running; it didn't cause any change until the ECM was reporting a 25 degree F difference which is a significant resistance error and even then it didn't fix the misfire, it just made it occur more often. I modified the resistance in both directions and it still took a reading of 25 or more degrees to make a difference. It's warm here so during a cold time of year it might make a larger difference at a lesser change but that isn't significant for this diagnosis. I'm retired so I have lots of time to experiment and the Fiero is my pleasure car, not my daily driver so time wasn't an issue for me. Heck, I enjoy solving these kinds of puzzles so it was fun, probably BECAUSE it isn't my daily driver. Again, the MAT is fine.
I rebuilt the TBI when I restored the car. There are no leaks, vacuum or fuel. Checked it many times during this diagnosis. Engine vacuum at idle is a very healthy 20 in-Hg. Which it should be since I rebuilt the engine about two years ago. Perfect compression, too.
I did NOT come to the conclusion that the MAP was the issue lightly. I checked everything else first because the MAP is the least likely...but it is possible and GM states that. My experience proves it. The misfire isn't that big of a deal, I just find it annoying and it likely won't hurt anything unless it gets much worse. I've proven with my scope that it is randomly on all four.
It is not any of the other things you've brought up, especially grounds because I redid all of that when I restored the car and have checked them multiple times during this diagnosis.
So once again, here we are: Same ogre crap, different day. Trying to make yourself feel good by obnoxiously discounting everything someone posts is not a good way to go through life. Which is why I rarely post and already regret this one. Just go away if you can't answer a simple question. I just wanted a simple opinion on brands of MAP sensors and maybe someone else's experience with buying ones that are bad out of the box since I got TWO bad ones. Not a bunch of your BS telling me how stupid you think I and everyone else is. Just go away. Far away.
I now fully understand the meaning of 2 Peter 2:16.
My question now is who makes a reliable replacement MAP for the Iron Duke? I've ordered one made by Standard since their parts usually work OK but I'm curious if anyone else has seen this problem? All three of them read 4.7V at KOEO (and 542 feet above sea level) and my scanner shows the idle value to be approximately 0.6V on the original and 1.1V on the "rich running" one. I didn't bother to check on the AC-Delco MAP since just starting it up proves it is crap!
Experimenting with starting it up using the original MAP and then using a vacuum pump to "trick" it into idling shows that when the voltage is at 0.8 the misfire goes away and raising it above 1.3V will cause it to throw DTC 45 so this tells me the original MAP is just a little out of calibration probably due to age...just enough to annoy me.
If I'm the only one experiencing this then I may play with adding an external reference circuit to tune it into range if the Standard version doesn't work. I hate to keep buying sensors since I'm currently 0 for 2.
Truth is all of these sensors are china made anymore. But to answer the question, I use Standard Motor Products, AC Delco Pro or AC Delco OE. Car seems to run fine on these and except for one oil pressure sensor in a Ford have had good life.
You make a valid point. I knew that and have gotten both good and bad stuff based on vendors when buying almost anything, such as electronic components.
It just surprised me when I bought the AC-Delco OE I expected to get a higher quality part and instead it wouldn't even pass the BARO test. GM sold it and even claimed it met their "rigorous quality control and specifications". I bought it from GMPartsDirect through Amazon and expected better. The cheaper part at least worked except for running rich at long idle times every so often.
Still waiting on the Standard part to arrive...USPS has permanently lost 4 packages sent to me this year alone and this one is overdue...not a good sign.
The problem with replacement sensors is that most are made in Communist China. Some are made in Mexico. This means you may get something very good or very bad. Henry, a friend of mine needed a new IAC valve and he purchased the AC Delco brand. He cleaned the throttle body, adjusted the pintle per the manual and it worked well for a month. Then his idle went haywire. He replaced it again and that one lasted a few weeks. Now his engine is idling at 3000 RPM. He hasn't tried a third replacement yet and he is going to the junkyard to try a used one.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
So once again, here we are: Same ogre crap, different day. Trying to make yourself feel good by obnoxiously discounting everything someone posts is not a good way to go through life. Which is why I rarely post and already regret this one. Just go away if you can't answer a simple question. I just wanted a simple opinion on brands of MAP sensors and maybe someone else's experience with buying ones that are bad out of the box since I got TWO bad ones. Not a bunch of your BS telling me how stupid you think I and everyone else is. Just go away. Far away.
Why so defensive? You've only posted 20 times in this forum. The Ogre doesn't know you from Adam. He doesn't know you or your capabilities. No need to take his post so personally. If you don't agree with or like his advice, just ignore it.
I take it personally when he DOES rudely attack others and make snide comments about their abilities and no one, including forum managers, call him out on it. He HAS criticized me personally more than once which is why I rarely post anything.
You are right, I shouldn't and I rarely do...except when it is him because he is so obnoxious and he does it on purpose.
I take it personally when he DOES rudely attack others and make snide comments about their abilities and no one, including forum managers, call him out on it. He HAS criticized me personally more than once which is why I rarely post anything.
You are right, I shouldn't and I rarely do...except when it is him because he is so obnoxious and he does it on purpose.
The person that you are referring to ,certainly has some strong opinions and some could call this being obnoxious. I just read over them as an opinion that may or may not be valid. Don't be bothered by these posts, just shrug it off and move on. Quite frankly I just laugh it off.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
Good advice, and that's what I usually do. Often, I just skip over his posts because they are usually a mixture of a little fact and lots of nonsense.
This one just ticked me off because it was absolute nonsense. Heck, I was looking for suggestions on a part, nothing else. I wanted the record set straight for anyone in the future that might have the same problem. All sensors in FI affect the A/F ratio therefore any misreading sensor can cause lean or rich conditions and that needed to be clear. My ranting was unfortunate yet I'd had enough that day.
Ok, two days of driving with the Standard brand MAP sensor and all is well. Moral of this story is that the quality of Chinese made sensors, even those branded AC-Delco, is low and chances of getting a bad one are too high.
So if you replace a MAP sensor and it acts differently yet not "right" then try another one and/or a different brand. Might be bad out of the box.
You've only posted 20 times in this forum. The Ogre doesn't know you from Adam. He doesn't know you or your capabilities. No need to take his post so personally. If you don't agree with or like his advice, just ignore it.
