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Horrible idle, MAF maybe?

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Horrible idle, MAF maybe?

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Old 11-21-2011, 03:39 AM
  #1  
91sport_tn
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Default Horrible idle, MAF maybe?

My 89 lx is backfiring and popping at idle. Sometimes it surges too.
Car has gt40 heads, cobra intake, E cam, 24lb injectors, 73 mm tb, and 73 mm c&l intake.

The previous owner put a different maf on there because it wouldn't run right with the stock one.

I drove the car a couple days(everything seemed fine) and it started surging, then it would fire up, rev and then die. we cleaned and swapped to the stock maf and it idled bad, so we cleaned and swapped back to the other one. A little better, but still about the same. At one point we tried to start it with one of the mafs unplugged, and it died.

At first, I thought the car just needed to warm up, but after a while of fighting to keep it running, I gave up. Does this seem like a mas air flow sensor problem to you guys? anything else it could be? I do not think it is a vacuum leak, and my next guess is IAC maybe?
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Old 11-21-2011, 12:38 PM
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ttocs
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IAC could cause it to die or idle high but it will not cause back firing.
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Old 11-21-2011, 01:29 PM
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Derf00
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Check the firing order

Check your timing (Most likely culprit especially since the heads are a swap) If the gears on the timing chain are not aligned properly or have broken teeth, a timing chain/gear change will be needed.

Check your fuel pressure (weak or dying fuel pump, or clogged filter)

IAC/MAF have nothing directly do with backfiring.

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Old 11-21-2011, 02:10 PM
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91sport_tn
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Originally Posted by ttocs View Post
IAC could cause it to die or idle high but it will not cause back firing.
Some times it will idle and other times it will not. at the moment it seems random.
The iac on there is a replacement, and the chance that it might help is reason enough for me to go on and get a new one from ford. I guess if it does not help, at least I know I have a new one on there.

Originally Posted by Derf00 View Post
Check the firing order

Check your timing (Most likely culprit especially since the heads are a swap) If the gears on the timing chain are not aligned properly or have broken teeth, a timing chain/gear change will be needed.

Check your fuel pressure (weak or dying fuel pump, or clogged filter)

IAC/MAF have nothing directly do with backfiring.
This is the first car I have got into this deep.
I'm not familiar with distributors, is there any way the firing order can get off without physically removing the plug wires and swapping them around?

I'll gheck the gears and timing when I can actually get under the hood during the day.

And, there is a gauge under the hood, that I think is the fuel pressure, it was reading about 40. does that sound right?
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Old 11-21-2011, 03:58 PM
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Originally Posted by 91sport_tn View Post
Some times it will idle and other times it will not. at the moment it seems random.
The iac on there is a replacement, and the chance that it might help is reason enough for me to go on and get a new one from ford. I guess if it does not help, at least I know I have a new one on there.



This is the first car I have got into this deep.
I'm not familiar with distributors, is there any way the firing order can get off without physically removing the plug wires and swapping them around?

I'll gheck the gears and timing when I can actually get under the hood during the day.

And, there is a gauge under the hood, that I think is the fuel pressure, it was reading about 40. does that sound right?
The firing order cannot be changed without physically removing wires and moving them around like you pionted out. Does the car feel like it's lacking power at higher RPM's? If it feels like that then definitely check the firing order as you have two cylinders that are swapped around, then check your timing. Otherwise, if power is not lacking at higher RPM, skip right to checking the timing.

Fuel pressure sounds about right.
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Old 11-21-2011, 07:26 PM
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Does the car still have an egr valve?

Last edited by TrimDrip; 11-21-2011 at 07:29 PM.
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Old 11-21-2011, 08:38 PM
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With the C&L Intake I am assuming it has a C&L MAF meter as well.... The car didn't run right before because there is no need for the 24lb injectors with what you have but I'm not saying to remove them.

You can not just open the hood and check your timing chain and gears. You have to remove the timing cover which also means draining the coolant and some other stuff.....

If the car ran perfectly fine and then started screwing up first run a KOEO/KOER test to get your codes and check for vacuum leaks. Then check all of your grounds to make sure all the connections are tight and clean. Pay close attention to the ground behind the battery...that is the EEC ground....

Check your TPS voltage..if your signal wire reads almost 5 volts then you don't have a ground in your computer for most of your sensors....then...

I would also check to see if your computer has fried pin 46.....
Get a multimeter and check continuity between the black wire at your TPS and a good ground on the body such as the metal tab on the firewall with your key on. If you have no continuity then turn the key off, unhook the battery, pull the passenger kick panel and unhook the computer. The do the continuity test with the key off from the same black wire to pin 46. If you then have continuity you need to get a new computer...
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Old 11-22-2011, 12:24 AM
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91sport_tn
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Originally Posted by Derf00 View Post
The firing order cannot be changed without physically removing wires and moving them around like you pionted out. Does the car feel like it's lacking power at higher RPM's? If it feels like that then definitely check the firing order as you have two cylinders that are swapped around, then check your timing. Otherwise, if power is not lacking at higher RPM, skip right to checking the timing.

Fuel pressure sounds about right.
problems actually seem to clear up at higher rpms, but im going to check the firing order to make double sure.

The computer can change the timing right? isit possible that it is changing it because of a bad sensor?

Originally Posted by TrimDrip View Post
Does the car still have an egr valve?
Not sure, I have yet to get a good look under the hood. I have worked every day since I bought the car. what are you thinking it could be?

Originally Posted by projectresto83 View Post
With the C&L Intake I am assuming it has a C&L MAF meter as well.... The car didn't run right before because there is no need for the 24lb injectors with what you have but I'm not saying to remove them.

You can not just open the hood and check your timing chain and gears. You have to remove the timing cover which also means draining the coolant and some other stuff.....

If the car ran perfectly fine and then started screwing up first run a KOEO/KOER test to get your codes and check for vacuum leaks. Then check all of your grounds to make sure all the connections are tight and clean. Pay close attention to the ground behind the battery...that is the EEC ground....

Check your TPS voltage..if your signal wire reads almost 5 volts then you don't have a ground in your computer for most of your sensors....then...

I would also check to see if your computer has fried pin 46.....
Get a multimeter and check continuity between the black wire at your TPS and a good ground on the body such as the metal tab on the firewall with your key on. If you have no continuity then turn the key off, unhook the battery, pull the passenger kick panel and unhook the computer. The do the continuity test with the key off from the same black wire to pin 46. If you then have continuity you need to get a new computer...
do the c&ls not have the calibrated tubes to work with the stock maf? or do those have to be bought separate? I didnt build the car, this is how I got it. He said it had 24lb injectors and they were running at 28 or something.

I assumed there was more to checking it, do you have to strip down the entire front of the engine to get to it?

the car was already throwing a cel because of the maf (is what I was told) but it ran perfectly fine. these problems seemed to happen suddenly checking for codes and vacuum leaks is at the top of my list, I'm just waiting for a day off, and I am glad you said that about the grounds. he changed the battery cables and something may be off somewhere.

Looks like I have some work to do on thanksgiving.. Hopefully I will be thankful for not having to buy a new computer...
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Old 11-22-2011, 08:56 AM
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It clearing up in the upper RPM's kinda helps part of the diagnosis.

You do need to double check the base timing. Make sure you remove the spout connecter when doing so.

C&L does have sampling tubes to "calibrate" for the injectors. The injectors running at 28lb? If I were you I would get a stock MAF and some 19lb injectors and see how it runs.

You can check your codes very quickly and easily. Then you will know for yourself what your possible issues are. No reason to go ripping into anything just yet.
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Old 11-22-2011, 06:44 PM
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+1 to getting a stock maf and injectors

Last edited by TrimDrip; 11-22-2011 at 06:48 PM.
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