MAF or IAC ?
09-08-2009, 12:52 PM
#1
Thread Starter
Join Date: Mar 2009
Location: CA
Posts: 18
Very hard to start 98 GT 4.6L SOHC ( IAT sensor ) ???
My 98 GT 4.6L 5spd has a problem again. I just replaced the Fuel pump problem w/great help from all the guys here. Thanks again for that.
Here is the problem. The car is very hard to start and don't like to stay running w/out intervention. I have to open the airfilter intake and spray some starting fluid in the intake for the car to start and run at idle. If and when I try to push the accelorator the car stalls. It then wont start again untill I give it another shot of starter fluid.
Could this be the MAF, TPS, IAC or IAT. Is there other culprits that could be causing this issue.
Edit: I got the car running w/some starting fluid and let it idle till it was warm then eased into the throttle to get the RPM's up and heat up the motor till the fan comes on. Then I shut the car off and it will start w/out starting fluid but it takes a couple of attempts to get it going.
So far I have checked the MAF and IAC and both seem to be fine. I unplugged the IAC while the car was running and the idle dropped instantly and returned to normal when I plugged it back in.
I also checked the voltage to the MAF at leads A & B and it was about 12.58 volts and the output voltage on leads C & D read about .72v or .82v at idle and increased with higher RPM's. So according to the Chiltons repair manual the MAF is functioning correctly.
I unplugged the IAT sensor and pulled it out to check the resistance and I get no resistance. I think this may be the culprit but I'm not sure and was hoping some one else here may have experience w/testing IAT sensors and how to determine w/out a doubt that is what the poblem is or is my symtoms sound like something else entirely different then what I'm looking at.
Edit #2: Well I took the IAT sensor to Autozone and compared it against two new sensors in the store and they all do the same thing which is nothing so I don't know what it can be.
Any help would be appriciated very much.
Here is the problem. The car is very hard to start and don't like to stay running w/out intervention. I have to open the airfilter intake and spray some starting fluid in the intake for the car to start and run at idle. If and when I try to push the accelorator the car stalls. It then wont start again untill I give it another shot of starter fluid.
Could this be the MAF, TPS, IAC or IAT. Is there other culprits that could be causing this issue.
Edit: I got the car running w/some starting fluid and let it idle till it was warm then eased into the throttle to get the RPM's up and heat up the motor till the fan comes on. Then I shut the car off and it will start w/out starting fluid but it takes a couple of attempts to get it going.
So far I have checked the MAF and IAC and both seem to be fine. I unplugged the IAC while the car was running and the idle dropped instantly and returned to normal when I plugged it back in.
I also checked the voltage to the MAF at leads A & B and it was about 12.58 volts and the output voltage on leads C & D read about .72v or .82v at idle and increased with higher RPM's. So according to the Chiltons repair manual the MAF is functioning correctly.
I unplugged the IAT sensor and pulled it out to check the resistance and I get no resistance. I think this may be the culprit but I'm not sure and was hoping some one else here may have experience w/testing IAT sensors and how to determine w/out a doubt that is what the poblem is or is my symtoms sound like something else entirely different then what I'm looking at.
Edit #2: Well I took the IAT sensor to Autozone and compared it against two new sensors in the store and they all do the same thing which is nothing so I don't know what it can be.
Any help would be appriciated very much.
Last edited by N2Gaming; 09-09-2009 at 01:22 PM.
09-09-2009, 01:58 PM
#3
2nd Gear Member
Join Date: Feb 2009
Location: Portland, Oregon
Posts: 324
well im not sure about your iat. but this seems like a fueling problem. like you said you just replaced your fuel pump, which leads me to believe you still have a fuel problem. have you checked your fuel filter? injectors?
09-09-2009, 06:06 PM
#5
Thread Starter
Join Date: Mar 2009
Location: CA
Posts: 18
The fule filter was replace w/the pump as I was told you replace both when replacing a pump to rule out problems down the road.
It seems that way after a day of no replies. I'm optomistic and hoping some one here can help me point the finger at the culprit.
I have 40psi at the fuel rail...
09-09-2009, 10:52 PM
#6
2nd Gear Member
Join Date: May 2008
Posts: 213
The starting issue could be a variety of things. Our starters get heatsoaked, so warm starts can cause problems like you described.
As for dying at idle, you'll need some form of datalogging to get a good answer. It could be timing retarded too far, dashpot bleeding off too much air, mixture too rich or lean (although that would throw codes), IAC being terrible and failing, spark issues, COP issues, or about a million other things.
I'm also not 100% clear on the rest of your problem. Are you saying that it always stalls when you give it gas (meaning the car just doesn't move anywhere) or that it only stalls when you don't give it gas at idle?
If you can do some data logging, it will be very helpful. With logging, you'll be able to tell a lot of important information, not the least of which is MAF voltage, MAF counts, STFTs and LTFTs at idle, and timing advance.
If you can't datalog for whatever reason, then I would start with the spark plugs (because they're cheap and easy to replace). Try to make sure each plug is firing correctly and none of them are fouled. From there, you can decide if it's an ignition problem or air/fuel delivery problem.
Good luck! post back with the results.
As for dying at idle, you'll need some form of datalogging to get a good answer. It could be timing retarded too far, dashpot bleeding off too much air, mixture too rich or lean (although that would throw codes), IAC being terrible and failing, spark issues, COP issues, or about a million other things.
I'm also not 100% clear on the rest of your problem. Are you saying that it always stalls when you give it gas (meaning the car just doesn't move anywhere) or that it only stalls when you don't give it gas at idle?
If you can do some data logging, it will be very helpful. With logging, you'll be able to tell a lot of important information, not the least of which is MAF voltage, MAF counts, STFTs and LTFTs at idle, and timing advance.
If you can't datalog for whatever reason, then I would start with the spark plugs (because they're cheap and easy to replace). Try to make sure each plug is firing correctly and none of them are fouled. From there, you can decide if it's an ignition problem or air/fuel delivery problem.
Good luck! post back with the results.
09-09-2009, 11:50 PM
#7
Thread Starter
Join Date: Mar 2009
Location: CA
Posts: 18
The starting issue could be a variety of things. Our starters get heatsoaked, so warm starts can cause problems like you described.
As for dying at idle, you'll need some form of datalogging to get a good answer. It could be timing retarded too far, dashpot bleeding off too much air, mixture too rich or lean (although that would throw codes), IAC being terrible and failing, spark issues, COP issues, or about a million other things.
I'm also not 100% clear on the rest of your problem. Are you saying that it always stalls when you give it gas (meaning the car just doesn't move anywhere) or that it only stalls when you don't give it gas at idle?
If you can do some data logging, it will be very helpful. With logging, you'll be able to tell a lot of important information, not the least of which is MAF voltage, MAF counts, STFTs and LTFTs at idle, and timing advance.
If you can't datalog for whatever reason, then I would start with the spark plugs (because they're cheap and easy to replace). Try to make sure each plug is firing correctly and none of them are fouled. From there, you can decide if it's an ignition problem or air/fuel delivery problem.
Good luck! post back with the results.
As for dying at idle, you'll need some form of datalogging to get a good answer. It could be timing retarded too far, dashpot bleeding off too much air, mixture too rich or lean (although that would throw codes), IAC being terrible and failing, spark issues, COP issues, or about a million other things.
I'm also not 100% clear on the rest of your problem. Are you saying that it always stalls when you give it gas (meaning the car just doesn't move anywhere) or that it only stalls when you don't give it gas at idle?
If you can do some data logging, it will be very helpful. With logging, you'll be able to tell a lot of important information, not the least of which is MAF voltage, MAF counts, STFTs and LTFTs at idle, and timing advance.
If you can't datalog for whatever reason, then I would start with the spark plugs (because they're cheap and easy to replace). Try to make sure each plug is firing correctly and none of them are fouled. From there, you can decide if it's an ignition problem or air/fuel delivery problem.
Good luck! post back with the results.
I have bosh super plugs in the car and am removing them one by one and finding black soot on all of them not to mention rust from when I pressure washed the engine compartment... I know
but it's to late to take it back so I has to deal w/it...In any case all your replies are apriciated to the fullest degree... LOL like that make any sense but I'm a Mustang Forum newb so what more can you expect from me.
I will reiterate for the last poster, the car starts up fine once it has been warmed up and does not have normal operating temperature starting issue. It has a cold starting issue...
Last edited by N2Gaming; 09-11-2009 at 04:40 AM.
09-10-2009, 05:55 PM
#9
2nd Gear Member
Join Date: May 2008
Posts: 213
Thanks a Ton... I think I can comprehend about a tenth of that. as far as dataloging, lets just say I can't because I don't know what the heck it is...
I have bosh super plugs in the car and am removing them one by one and finding black soot on all of them not to mention rust from when I pressure washed the engine compartment... I know but it's to late to take it back so I has to deal w/it...
In any case all your replies are apriciated to the fullest degree... LOL like that make any sense but I'm a Mustang newb so what more can you expect from me.
I will reiterate for the last poster, the car starts up fine once it has been warmed up and does not have normal operating temperature starting issue. It has a cold starting issue...
I have bosh super plugs in the car and am removing them one by one and finding black soot on all of them not to mention rust from when I pressure washed the engine compartment... I know
but it's to late to take it back so I has to deal w/it...In any case all your replies are apriciated to the fullest degree... LOL like that make any sense but I'm a Mustang newb so what more can you expect from me.
I will reiterate for the last poster, the car starts up fine once it has been warmed up and does not have normal operating temperature starting issue. It has a cold starting issue...
Also, sooty rusty spark plugs certainly aren't helping anything. I would be willing to wager that this is the cause of all of your problems. Getting water in the engine electronics, spark plugs, etc is a surefire way to cause all sorts of headaches. Your plugs should be an ashy-white/gray color, so if they're black and sooty then you may have combustion problems (which may be caused by the bad plugs).
Replace the plugs immediately. The problem should get better if not completely go away. After that, you can try to make sure each plug is firing and make sure there is no other damage from pressure-washing the engine bay.
And, I'm sure this goes without saying, but don't pressure wash your engine again
.
09-10-2009, 09:58 PM
#10
Thread Starter
Join Date: Mar 2009
Location: CA
Posts: 18
I don't have a odb II scanner or any type of data loging software. Is this something that I would use on a laptop or something along those lines.
I don't plan on pressure washing this car ever again, well not the engine bay any way at least not while there is a engine in the car.
Yeah I forgot to mention. The cold start issue did rear it's ugly head after letting is sit for a while after pressure washing it.
I just finished pulling the plugs and doing a compression test on all of the cylinders and it turns out cyl 2-3 are low at 165 & 140 but cyl # 8 is at 75...
I don't plan on pressure washing this car ever again, well not the engine bay any way at least not while there is a engine in the car.
I just finished pulling the plugs and doing a compression test on all of the cylinders and it turns out cyl 2-3 are low at 165 & 140 but cyl # 8 is at 75...
Last edited by N2Gaming; 09-11-2009 at 04:35 AM.