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Discussion Starter #1
hey guys,

Recently picked up a 90 LX 5.0. Has gt40 3 bar heads, crane 274 cam, explorer intake, afpr, and all the supporting mods. The egr has been deleted. Running stock injectors and MAF. I've done new wires and plugs, nothing looked bad on the plugs I removed. They were whiteish with no carbon buildup. I'm getting 40psi at the fuel rails with the vacuum unhooked. Getting around 12-14 inches of vacuum at idle, no vacuum leaks. I pulled the upper intake and checked. I haven't checked the timing but was told by the PO it was set at 12 degrees. I haven't changed the fuel filter, cap or rotor because it was done a year ago, but i will change them tomorrow just to rule that out. Haven't pulled codes, need to do that as well. When the car gets up to temp, under load it starts stumbling. Almost as if its running out of fuel. However when it's cold, it has no issues at all. Starts up great, runs great under load. I thought it was a fuel related issue,but that seems like it would be doing it all the time. Anything over 2,500 rpm the car will sputter it sounds like its back firing through the intake. Seems like it does this when it goes into closed loop. I haven't checked the tps either, I will do that tomorrow as well. The car runs too good when not up to temp, thats what is making me think its not a mechanical or fuel issue. I get steady vacuum at 1000 rpm, so I don't think its a stuck valve. I've done a compression test and its 170\180 across the board. Has a clean stock MAF as well. I'm stumped. Fuel mileage is in the gutter as well.

Thanks for any help.
 

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you have a misfire

check codes first


sounds fuel related

do not start swapping parts

and when you say 'supporting mods' what does that mean?

i see no tuning device listed
 

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If when it is cold (open loop) and then warm (closed loop) then sounds like some sensor starts reporting bad numbers and the ECU doesn't like it. I am no pro but I would research that a little.
 

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Discussion Starter #4
Stock ECU, no tuning device.
I will check codes tomorrow. Basic supporting mods for the car, 190 fuel pump, TB, CAI, ect. Car has 80k original miles on it, and hasn’t been beaten to death. I figured it’s a mis fire due to fuel. Wondering if it could be 02 related.
 

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Discussion Starter #5
Yeah I agree. Only a few sensors come to mind that has a big part of that, TPS, MAP, 02 sensors. Car doesn’t have any smog or emissions on it. I’m sure it’s throwing codes from that.
 

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could be anything

broken injector ground........who knows, its called diagnosing

measure voltage on both 02 signals by back probing at the ecm

see if they are switching

when an 02 is fixed high or low, a CEL will be flashing you in the face as you drive

removing the smog and egr was just foolish.......so who knows
 

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Set that fuel pressure to 43.5 psi while you’re at it.


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Discussion Starter #8
It’s called diagnosing? Oh, ok, gotcha! Why was it foolish to remove the smog and egr? Last time I checked, the title is in my name.
Thanks for the advice.
 

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I would not go that drastic just yet, I know it is easy to do that kind of repair, just throw parts at it but that is half the reason why we have these old cars is to throw wrenches around the garage and kick garbage cans while we cannot figure things out! haha been there so many times :ROFLMAO:

Removing smog IMO was not foolish, thousands of people have done it me included and have had no issues. Just focus on sensors and voltages, maybe visual inspection to make sure a mouse didn't get in there and have a meal.
 

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Discussion Starter #11
Yeah I know what you mean. I have a LSx powered F100, and I can plug in my HP tuners or EFI live and instantly see what’s going on, or if I need to make any adjustments. Can’t do that on this OBD1 ecu. It’s definitely a sensor, maybe something did come unplugged? I’m going to take the upper back off and look around. I will test the tps voltage, and 02 sensor. The car runs too good for it to be something mechanical.
 

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Removing smog IMO was not foolish, thousands of people have done it me included and have had no issues.

sure IS

just because there are thousands of yous dont make not foolish

its right up there with pulling the a/c system and going manual steering,
 

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Did you check codes yet?

Looking to point you in the right direction with the least amount / zero criticism.

Some people just enjoy swapping parts if they have the parts, or don’t have time to properly diagnose.

I like to spend the time & properly diagnose, but that’s just me.

Anyway, post what you’ve found and I will help how I can.


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Just bc you think it is foolish doesn't make it foolish (y)

because i said it is, it sure does.

If you took the time to do the slightest amount of research into it, you would as well, maybe
 

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No it's not O2 related. Pull the vacuum hose on the fuel pressure regulator and see if it's wet. I've seen a lot of them go bad and pull fuel through the vacuum hose. Cold it runs okay because cold engines like to run rich anyway, hot engine it's just pig rich and runs bad.

Does it run bad only in gear, can you free rev it fine when it's acting up? Coils also tend to act up when hot and under load but would usually be fine cold or light/no load.
 

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Discussion Starter #18
No it's not O2 related. Pull the vacuum hose on the fuel pressure regulator and see if it's wet. I've seen a lot of them go bad and pull fuel through the vacuum hose. Cold it runs okay because cold engines like to run rich anyway, hot engine it's just pig rich and runs bad.

Does it run bad only in gear, can you free rev it fine when it's acting up? Coils also tend to act up when hot and under load but would usually be fine cold or light/no load.
I pulled the vacuum hose the other day when I set the fuel pressure. Didn't notice it wet. I will check again. I can free rev the motor while warm and its not noticeable. Only under load at operating temp it acts up. Been busy with other projects , I plan on jumping back on it in the next day or two. I ordered a cheap obd1 scanner to pull codes.
Interesting you mention a coil. The previous owner changed the coil with a new accel coil. He told me the only problem he had with the car is the coil went out and wouldn't start.

Thanks for the help.
 

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Discussion Starter #19
Did you check codes yet?

Looking to point you in the right direction with the least amount / zero criticism.

Some people just enjoy swapping parts if they have the parts, or don’t have time to properly diagnose.

I like to spend the time & properly diagnose, but that’s just me.

Anyway, post what you’ve found and I will help how I can.


Sent from my iPhone using Tapatalk

Apparently peoples lifes are so pathetic all they want to do is jump behind a keyboard and become a warrior. I have a OBD scanner coming in to pull codes. Its been a while since I've diagnosed the foxbody platforms , I know they can be a pain at times.
Will keep you updated here in the next day or so.
 

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Money says it's the coil then
 
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