Modded Mustang Forums banner

Rough Running (rich A/F ratio?)

6.7K views 12 replies 4 participants last post by  Danno  
#1 ·
Hello guys,

First off I will say I'm am new to this forum and bought my first Fox body (88' GT) a couple months as a project. The state of the car when I picked it up on the cheap was the motor (5.0 with T5) was out of the car ready to dropped in. Over the span of a couple months, I installed the engine. (this forum helped a lot with the process!) Long story short, i got it started, but it runs very rough. When it does fire up (not all that often), quite a lot of gray smoke come from the exhaust (good sign that it is not white (coolant) or blue (oil)). This smoke combined with that the exhaust smells of gas leads me to believe it is running VERY rich.

I towed it to a shop last week to look at because I am on a business trip till Friday, but I just got a call from them saying that they looked at it, weren't making any progress after a couple hours, so they essentially gave up. (lame, but at least they aren't charging me anything.) Here is what I believe is causing it to run so effing rich: the previous owner deleted a whole lot of stuff in order to free up more horsepower. EGR, smog, AC (still there, but not hooked up), but most importantly, the heater assembly. So there is nothing for me to plug the coolant temp sensor for the ECU into. Am I correct in assuming that this screwing with the computer's ability to correctly estimate the air/fuel ratio? It could also explain why it will only start when it is cold. (constantly choked in essence) Has anyone ever not run the coolant temp sensor without problems?

Also, regarding the EGR and smog, the spacer between throttle body and the intake is properly blocked off with a delete plate (so now there is nothing to connect the EGR plug to) and the smog pump/related plumbing has been taken out and a delete pulley is in it's place. The only thing left and plugged in is the EGR solenoids, but they are not hooked up to the vacuum anymore, so I assume there aren't affecting anything, but I'm really not an expert with these engines.

Any help here would be greatly appreciated. I see great potential in fixing up the Stang, but I got to get it running first.

Dave
 
#2 ·
There are other ports on the intake that you should be able to screw the coolant temp sensor into. For example. The black heater tube that you said was removed. Screw the sensor in where that was. If the thread size is not the same buy an adapter to make it fit.
 
#6 ·
Not sure, but if the o2 sensors are original, I'd replace them.

Are you still running the stick 19lb injectors, they have orange tops. I'd also check your fuel pressure, do you have an adjustable fuel pressure reg. ???
 
#8 ·
9 times out of 10 when people are having A/F problems its the o2 sensors. It could very well be something else, but it's the best place to start. Those directly control the A/F mixture.
 
#9 ·
Sorry, I forgot to mention I put in new HEGO (O2) sensors. I not sure if this is worth mentioning, but I have long tube headers without a crossover/h pipe, or any cats. Not sure how this would effect the oxygen in the exhaust at all. I suppose I could also check and make sure they are grounded well (it grounds to the firewall correct?). The shop told me they weren't able to pull any codes with their meter, but that might not be as reliable as the good ol' blinking light method. I'll try that if the heater tube/coolant temp sensor and the O2 grounds don't fix it.
 
#10 ·
Cats don't make a difference on your o2 sensors because the o2 sensors are before the cats any ways.
 
#12 ·
Fuel pressure should be around 39 psi with the vacuum line disconnected from the pressure reg. Make sure you plug the vacuum line coming off the intake when doing this test or you'll have a vac leak.
 
#13 ·
My 92 LX is running rough too (it's in the shop getting tuned as I write this), so if and when I find out what's going on, I'll make sure to post as it might help you. Mine is running lean and surging at idle though - so although related, it sounds like it's the opposite of your issue. Either way, I'll let you know what comes of it...