Engine Sligh miss and pop over 3k rpm

Png1978

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Dec 29, 2017
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Hello I have a 1988 mustang GT California mass air car. It has a slight miss/pop under heavy load when over about 3k rpms. Never does it under regular driving and part throttle. Seems to only be when Under wide open throttle.

In the process of restoring the car I replaced

Fuel PuMp
Fuel filter
Plugs (twice)
Wires (twice)
Coil
Cap and Rotor
Replace H-Pipe with BBK catted one
Replaced O2 sensor.

Mass Air meter but the same sensor. Unfortunately I can’t change the sensor unless I go splicing the plug. 88 mass air cars Cars have a square plug. I might be able to hunt one down but all the places I looked was a round one. All other mustangs are round. I did Clean it though.


I’m kind of stumped at this point has to what it could be.

My thoughts are something with the dizzy. Pip sensor perhaps. Tried a different TFS module. No real difference. The car seems to do it cold and hot Makes me think TFI is fine. I heard they normally only give problems when hot.

I’m not sure if the EGR valve could be casueing this. I do notice the EGR makes some funky buzzing sounds at idle.

My other thoughts are it’s could be injectors or fuel regulater.

The miss and pop is not that noticble. Like it’s not bucking or hesitating real bad so that makes me think it’s not fuel related. At least it’s not starving for fuel.

I also tried different timing any where from 10 to 14 degrees. Still does it

Any thoughts on what this could be?

Could a mechanical issues cause this? Car has about 200k on it. Other than that it runs great and still pulls hard.

I’m not sure if this is accurate but it feels like it’s only the driver side exuast doing it. It could just be i can’t hear the passenger side doing it because I’m hearing the driver side exhaust.
 
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T5live

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Oct 2, 2020
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Douglas Ga
Man I’m having the same problem and I can tell you I don’t have a roller motor probably the only two thing that our cars will have in common or mass airflow in factory 50 injection just to let you know mechanical problems can cause this do you have any blow by any smoking? I am a master tech and honestly I’m a little stumped to I pulled valve covers and checked all But at that time it just didn’t feel like acting up on the lift I guess it wasn’t enough load on it. do you have any EGR codes?
 

Png1978

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Dec 29, 2017
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Man I’m having the same problem and I can tell you I don’t have a roller motor probably the only two thing that our cars will have in common or mass airflow in factory 50 injection just to let you know mechanical problems can cause this do you have any blow by any smoking? I am a master tech and honestly I’m a little stumped to I pulled valve covers and checked all But at that time it just didn’t feel like acting up on the lift I guess it wasn’t enough load on it. do you have any EGR codes?
I don’t have any smoke. Car does use some oil. The hesitation is also intermittent. That makes me thinks it’s not mechanical. It seems to do it more when hot then cold.

So yea I got codes 34, 41, 91.

34 has something to do with the EGR valve or sensor. I checked the ground on the sensor and they look good. Might just buy a new EGR valve and sensor. I did cap the vaccum off to the egr and the car still did it.


41 and 91 are left and right bank lean. The O2s are fairly new. The car did it before them to. Some one said check the ground on the 02s. I attached a pic of what I think the ground is. Maybe some one can chime in if that’s it.

I don’t see how the EGR could be causing the issue though unless it’s stuck open some. From my understanding it’s suppose to be closed at Wide open throttle.

The hesitation isn’t that bad. Like the car still pulls pretty hard. Its just annoying and there is a very faint popping coming from the exhaust. Car idles fine and drives just fine.
 

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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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polk county florida
Here are steps and explanations on fixing surging,idle,stalling and may help you with your 'lean' issue.
Another thing with 200k on the engine the valve springs could be weak and not able to keep the valves closed at high rpms causing the lean codes. Just thinking out loud.
 

Png1978

Member
Dec 29, 2017
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6
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Here are steps and explanations on fixing surging,idle,stalling and may help you with your 'lean' issue.
Another thing with 200k on the engine the valve springs could be weak and not able to keep the valves closed at high rpms causing the lean codes. Just thinking out loud.

I have thought about that has well about the heads. But then It will pull those codes doing the kEy on Engine running test. So it pulls them at idle to.

Thought about doing a rebuilt motor or heads. Im kinda like I want to see how many miles a 5.0 will last though....‍♀️Need to catch my brothers old 4 runner with 450,000 on it
 

Png1978

Member
Dec 29, 2017
55
6
8
42
Here are steps and explanations on fixing surging,idle,stalling and may help you with your 'lean' issue.
Another thing with 200k on the engine the valve springs could be weak and not able to keep the valves closed at high rpms causing the lean codes. Just thinking out loud.
Thanks for the list to
 

HemiRick

Active Member
Jun 28, 2020
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Memphis TN
Your symptoms are completely in line w a typical TFI failure mode, TFI's will work but miss at high rpm.
 

Png1978

Member
Dec 29, 2017
55
6
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42
Your symptoms are completely in line w a typical TFI failure mode, TFI's will work but miss at high rpm.
I was looking at getting a new TFI. I noticed they say for manual. My car is a automatic. Is there really a difference? I have never seen a ford one that says automatic.
 

Png1978

Member
Dec 29, 2017
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Your symptoms are completely in line w a typical TFI failure mode, TFI's will work but miss at high rpm.
So did some research looks like the TFI is the same for the auto or manual. It’s a part classification error.

I did take the car for a spin earlier and it happenes right around 3500 rpm. Never before that.
 

T5live

Member
Oct 2, 2020
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2
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35
Douglas Ga
I don’t have any smoke. Car does use some oil. The hesitation is also intermittent. That makes me thinks it’s not mechanical. It seems to do it more when hot then cold.

So yea I got codes 34, 41, 91.

34 has something to do with the EGR valve or sensor. I checked the ground on the sensor and they look good. Might just buy a new EGR valve and sensor. I did cap the vaccum off to the egr and the car still did it.


41 and 91 are left and right bank lean. The O2s are fairly new. The car did it before them to. Some one said check the ground on the 02s. I attached a pic of what I think the ground is. Maybe some one can chime in if that’s it.

I don’t see how the EGR could be causing the issue though unless it’s stuck open some. From my understanding it’s suppose to be closed at Wide open throttle.

The hesitation isn’t that bad. Like the car still pulls pretty hard. Its just annoying and there is a very faint popping coming from the exhaust. Car idles fine and drives just fine.
That is just a chassis ground strap it does it actually ground directly to the O2 sensors let me do some looking at some schematics and I’ll let you know where the ground to the o2 goes and try to give you some information It will be Monday before I’m back at work in front of my computer I have everything on have you done any intake work recently and is the screen under your PCV clean I am getting down to the nitty-gritty on this problem I have been going at it pretty hard for the last week because it just irritates me I’ll try to remember to get the information Monday if you happen not to see a post or something from me post a little something to remind me I’m horrible about forgetting things sometimes
 

T5live

Member
Oct 2, 2020
15
2
13
35
Douglas Ga
That is just a chassis ground strap it does it actually ground directly to the O2 sensors let me do some looking at some schematics and I’ll let you know where the ground to the o2 goes and try to give you some information It will be Monday before I’m back at work in front of my computer I have everything on have you done any intake work recently and is the screen under your PCV clean I am getting down to the nitty-gritty on this problem I have been going at it pretty hard for the last week because it just irritates me I’ll try to remember to get the information Monday if you happen not to see a post or something from me post a little something to remind me I’m horrible about forgetting things sometimes
But my car does it under the exact same condition as the car had no thermostat in it when I got it so it wouldn’t idle quickly and it drove really hard once I put a thermostat in shortly after this problem started and all I did was put a thermostat in don’t know if that helps you any just thought I’d mention it
 

Png1978

Member
Dec 29, 2017
55
6
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42
That is just a chassis ground strap it does it actually ground directly to the O2 sensors let me do some looking at some schematics and I’ll let you know where the ground to the o2 goes and try to give you some information It will be Monday before I’m back at work in front of my computer I have everything on have you done any intake work recently and is the screen under your PCV clean I am getting down to the nitty-gritty on this problem I have been going at it pretty hard for the last week because it just irritates me I’ll try to remember to get the information Monday if you happen not to see a post or something from me post a little something to remind me I’m horrible about forgetting things sometimes
No have not done any work on the intake. I replaced the screen and PCV valve already. I did buy a used Ford distributor off eBay today. Going to try the TFI module off it and see if there is any difference. maybe rebuild that Distributor with new PIP sensor later on has well.

Some people have suggested the TFI or PIP sensor can cause some high end missing. I also have a new coil and cap and rotor coming. Although I have tried another coil already.

I just bought those because I got a good deal on them. $30 lol

Yea I need to find that ground and make sure it’s good and clean it. After looking through the forums ground issues with The 02 can cause the 41 and 91 code.

I’m also going to look at the harness and clean it. The old 5.0 does have some oil leaks so maybe the connection on the harness is dirty causing a bad connection. I know it has a connector on the other end somewhere.
 

Png1978

Member
Dec 29, 2017
55
6
8
42
That is just a chassis ground strap it does it actually ground directly to the O2 sensors let me do some looking at some schematics and I’ll let you know where the ground to the o2 goes and try to give you some information It will be Monday before I’m back at work in front of my computer I have everything on have you done any intake work recently and is the screen under your PCV clean I am getting down to the nitty-gritty on this problem I have been going at it pretty hard for the last week because it just irritates me I’ll try to remember to get the information Monday if you happen not to see a post or something from me post a little something to remind me I’m horrible about forgetting things sometimes
The other thing I would say is I have had this problem for 2 years. Have not really tried to fix it other then basic tune up stuff. Plugs, wires, cap, rotor. I did replace the fuel pump with a 110 walboro because it had a crappy auto part store one in there.

The problem originally started when I had that old fuel pump in there.

The problem has not gotten any worse either. I find that to be interesting. You would think if it was a failing part the part would have detiriated even more causing more hesitation.
 

Png1978

Member
Dec 29, 2017
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And I have lean codes also and o2 switch. By the way how experience do you have?
Well I’m not a mechanic. I’m A IT field engineer so I do lots of troubleshooting type stuff just in a different environment. Mainly networks, computers, servers stuff like that.
 

T5live

Member
Oct 2, 2020
15
2
13
35
Douglas Ga
Well that’s kind of nice to know I started in IT back in 1999 right out of college and quickly went from someone that tune ECM’s on the side to someone who repair and built cars and now I’m in automotive tech. Tuner cars and turbos were my life for quite a while then Camero‘s and LS and I just wanted to do a 5.0. However if it can’t get right I’m going to go to what I know got a built LS 4.8 got stuck with from another project and I can use it still keep the T5 so. Back on subject I’m going to put in a new TFI today I’ll let you know what comes about with your lean codes are you on the stock mass air flow and injection?
 

Png1978

Member
Dec 29, 2017
55
6
8
42
Well that’s kind of nice to know I started in IT back in 1999 right out of college and quickly went from someone that tune ECM’s on the side to someone who repair and built cars and now I’m in automotive tech. Tuner cars and turbos were my life for quite a while then Camero‘s and LS and I just wanted to do a 5.0. However if it can’t get right I’m going to go to what I know got a built LS 4.8 got stuck with from another project and I can use it still keep the T5 so. Back on subject I’m going to put in a new TFI today I’ll let you know what comes about with your lean codes are you on the stock mass air flow and injection?
The injectors are stock and the mass air sensor is stock. The housing is a C%L meter. It did all this on a stock houseing has well though.

I did clean some grounds the other day and cleaned the mass air sensor connector
With some electrical cleaner and the car ran way better afterwards.

I got codes 34, 41 and 91. The 34 is something with the EGR sensor being out of voltage range. I might pull the EGR off and clean it.

One of the tech how to threads says if ya get 34 it’s either the sensor on the EGR is bad or there is carbon build up on EGR valve. IAm assuming holding it open some. I really need to just find another EGR valve and sensor to test with or just buy some new ones.

If I’m understanding the EGR correctly it’s suppose to be closed at idle and WOT. I also read that the O2 sensors are not used at Wot because the computer runs in closed loop.

I also want to do a vacuum leak test with a smoke machine. I have been looking online at some little fogger pins that are used for checking air flow. I guess in Air conditioning world lol.....they send out tons of fog so I could connect that to the vacuum tree. It’s that or build a smoke machine out of something.

I don’t like the throttle body cleaner method since it can go poof with flames. I heard soapy water can work to.
 

Png1978

Member
Dec 29, 2017
55
6
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42
Well that’s kind of nice to know I started in IT back in 1999 right out of college and quickly went from someone that tune ECM’s on the side to someone who repair and built cars and now I’m in automotive tech. Tuner cars and turbos were my life for quite a while then Camero‘s and LS and I just wanted to do a 5.0. However if it can’t get right I’m going to go to what I know got a built LS 4.8 got stuck with from another project and I can use it still keep the T5 so. Back on subject I’m going to put in a new TFI today I’ll let you know what comes about with your lean codes are you on the stock mass air flow and injection?
Ah that’s cool. Those LS engines are good engines. I seen this dude on you tube with one in a old cargo van. Like a full size van. It had tons of miles to. He stuck a cam in it and some nitrous and was running 11s if I remember correctly. It was pretty funny because the engine had so many miles the oil pressure was shot but it was still slinging that van down the track.
 

T5live

Member
Oct 2, 2020
15
2
13
35
Douglas Ga
It’s funny you should say that the LS motor I got a pulled out of a suburban with 230,000 miles and the lady said she never change the oil I checked it over put a new old pump in it and screen through the hot cam in it stock head still modifications to the rocker assembly and it ran hard in a Mercury Capri body for about six months at the track will twin 66 mm Grady‘s on it they call me turbo Dave but I’m actually a nitrous over turbo or supercharger guy I like twice the power if I can get it it’s only an eighth or a quarter mile at a time just for :poo:s and giggles what gears do you have under your Mustang I went to 373‘s and it was a huge change from stock but I’ve been wondering about some 355s because I think I may run out of car in a quarter mile right now I’m actually at my shop right now putting a TFR on the car just a cheap one to see if it changes anything and then I’ll decide what nicer one to buy if it is the fixI’ll post again soon and let you know
 

Png1978

Member
Dec 29, 2017
55
6
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It’s funny you should say that the LS motor I got a pulled out of a suburban with 230,000 miles and the lady said she never change the oil I checked it over put a new old pump in it and screen through the hot cam in it stock head still modifications to the rocker assembly and it ran hard in a Mercury Capri body for about six months at the track will twin 66 mm Grady‘s on it they call me turbo Dave but I’m actually a nitrous over turbo or supercharger guy I like twice the power if I can get it it’s only an eighth or a quarter mile at a time just for :poo:s and giggles what gears do you have under your Mustang I went to 373‘s and it was a huge change from stock but I’ve been wondering about some 355s because I think I may run out of car in a quarter mile right now I’m actually at my shop right now putting a TFR on the car just a cheap one to see if it changes anything and then I’ll decide what nicer one to buy if it is the fixI’ll post again soon and let you know
So my car is a convertible aod so I don’t really race it. Lol....although the aod was built to handle some power by previous owner and has a shift kit in it.


Just cruise and daily drive it. It had 3.73 when I got it. Had the rear end rebuilt with 3.23 because I drive allot on highway. Like some times 2 hours or so. Then I changed over to 3.55 and put a aluminum drive shaft in. I like the 3.55 the best. Still gets up some but doesn’t annoy me on the highway.

Car also has 31 spline axles and a Eaton posi. I need to take it to the shop though and have the guy rebuild the posi. Its making some noises and the axles have some play in them. The rear end guy I use says the posi needs a rebuild.

I’m getting ready to drive 2200 miles across country so I’m doing has much has I can before I head out in a month.