Speed Density Vs. Mass Air

[LOVEMY88GT]

Hi I have a 1988 Mustang GT. Its got the 5.0L and it is a 5 speed manual. I have done a number of mods to it lately. And now it is just gone real bad. The problem I am having is that it has this hesitation and when it does that then if you press the gas harder it backfires or pops. So I have done a number of things to try to get it to stop. (New Spark Plugs, Temp Valve, Throttle Positon Sensor, GHR Valve, new coil, fuel filter, and 20 bucks of fuel system cleaner) And guess what it still does about the same thing. So my conclusion now is that I should get the Mass Air Conversion Kit. I think this because I hear of people having some problems kind of like this. The things that I have done to it from stock is Flowmaster 3in, Mach Long Headers, Mac Offroad H-Pipe, Accel Wires, K&N Filter, Super Coil. Thats about it other then just some visual mods. So i am wondering because now that I have changed the whole Exhaust System it set off the speed density. Because Before it never did that like it does now. So if you know anything it would really help me out. THANKS!!!!

~Nick

[GTStang]

Your parts cause no problem for a Speed Density car.

[duplox]

Did you take the oxygen sensor off the car when you put the new headers on? Taking off the o2 sensor will make the computer blind to how well it is metering fuel... So all it has left to base its readings on are basically manifold pressure/vacuum, throttle position, air, RPM, and coolant temps. If you didn't make any mods to the motor and took out the o2 sensor, it'd probably do fine, since the fuel maps were programmed for a stock motor... but once you increase the volumetric efficiency(like adding headers/h-pipe.. all the other stuff won't really increase performance.), the computer will inject too little fuel, since it still thinks your motor is stock. I'm not sure exhaust will be enough to throw it off that bad, but maybe? With an o2 sensor it should be able to compensate since you have such minor changes.

Another thing - Ignition timing is controlled by the Ford computer, right? maybe since it is injecting too little fuel it causes detonation, which it responds to by retarding the ignition.. too little fuel + retarded ignition = lots of popping and backfiring. it happened on my carb'd motor, I couldn't put it past 1/2 throttle without it backfiring.

[LOVEMY88GT]

ya thanks well I did take the o2 sensors off and put on new ones so what should I do so that the computer is not blind????

THANKS!!!

~NICK

[LOVEMY88GT]

Alright so what do you think I should do I mean I put new ones on and now i told you the stuff I did and I am thinking if I put on the new mass air converson kit it would be able to adjust to this I heard

[GTStang]

Originally Posted by LOVEMY88GT

Alright so what do you think I should do I mean I put new ones on and now i told you the stuff I did and I am thinking if I put on the new mass air converson kit it would be able to adjust to this I heard

If you put new or the original 02's back on and hooked them up correctly Speed Density will adjust to headers and exhuast fine. It is well within the fuel maps of the stock SD ECU. Doing a MAF conversion will not fix whatever problem your have with the car.

Speed Density will only have issue with mods when you cause erratic manifold pressure or you create enough fuel need beyond the stock fuel map values and variable values. Niether of these are the case from your mods.

[LOVEMY88GT]

So what do you think would be causing all this right after I changed exhaust? I just want to know that. And I know it is some kind of a computer problem because it does not do it all the time. But then it will start to do it and it is like the plague you give more gas and it pops some and then VOOM!!!! I like the VOOM!!!! alot but I just hate the popin and backfire it is doing with it. Any other segestions? Thanks

[LOVEMY88GT]

So you think maybe I might have put on the o2 wrong? I mean I checked them again. I dont know what else to do and the Mass air looked like a nice excape but maybe it is something as simple as the o2 sensor you think?
Thanks!!!

[GTStang]

Hesitation and backfiring and popping sounds like the car is misfiring to me. Pull your plugs and read them also make sure you have the proper plugs and heat range. Check your intial timing with the spout disconnected. Also check your plug wires with the old screwdriver agiainst metal trick.

[LOVEMY88GT]

Ya I just got new plugs and the wires are fairly new. And the main thing that makes me think it is a computer problem is that it does not do it all the time. Like it will be really fast and then a few minutes later it will have the hesitation and if you give it more gas it will start to pop and then it will back fire. After that it will Zoom forward. So thats why I think it may be a computer problem. I will look at those things today but I am still edging toward the computer.

[HiFlow5 0]

I think your problem is your 3" exhaust! Way too big for a stock motor car, you don't have enough mods to support the lack of backpressure that big exhaust has. What size long tubes did you buy as well?

[duplox]

1) engines do NOT like exhaust backpressure. The reason you want smaller pipes on a lower revving motor is it improves exhaust scavenging in the chambers at low RPMs. Sorry, but I've heard this one too many times.. I can let it slide so many times, but eventually it gets to me.
2) I think he meant he's got 3" collectors on the headers, which is what pretty much all long tube headers have. Then you usually use 2 1/2" dual after the headers. Thats what I use.. If he does have 3" exhaust piping after the headers, I agree, he should get smaller. It will hurt scavenging and reduce power.

[LOVEMY88GT]

My bad I got 2 1/2 inch. So what do you think now. Well I got all the stuff done professionally and MustangsUnlimited got it all customed just for my car adn then I had the shop do it all up with it all. So i know there is nothing rong with the pipes I really think it the computer that is doing it because it does not do it all the time. So I have heard that the Mass Air controls things like the spark, ignition, air, fuel mixture, volume of the air and all kinds I heard like 5 different molecules in the air. Speed density is set with the stock maps. I really think it is a computer problem. SO what do you think?
THANKS!!!

[LOVEMY88GT]

If you want pictures just tell me and I will put some on here.

[GTStang]

Originally Posted by LOVEMY88GT

My bad I got 2 1/2 inch. So what do you think now. Well I got all the stuff done professionally and MustangsUnlimited got it all customed just for my car adn then I had the shop do it all up with it all. So i know there is nothing rong with the pipes I really think it the computer that is doing it because it does not do it all the time. So I have heard that the Mass Air controls things like the spark, ignition, air, fuel mixture, volume of the air and all kinds I heard like 5 different molecules in the air. Speed density is set with the stock maps. I really think it is a computer problem. SO what do you think?
THANKS!!!

Here is a question I should have asked before but have you scanned your car for codes?