Anyone hate speed density as much as I do?

[RangerFabWorks]

So I picked up a 1991 f150 5.0 automatic. Long story short. 93k miles. Barely ever driven. Super clean truck.

I did the usual. Plugs. Wires. Coil. Cap. Rotor. Air filter. Fuel filter. O2 sensor. And map sensor. Clean the throttle body and iac. And I replaced the entire exhaust.

truck runs great. But has a very slight miss at idle. And the cel will come on and off while driving. The only codes it throws are for the egr valve. I’ve replaced it with a known good one. And no real change.

someone convince me not to rip all this crap off and slap a 4bbl on it!

 

[Dirtman]

Carbed engines still use EGR valves, they just don't have a computer to tell you it's broken...

Which, makes one wonder.... what part of the egr system has a sensor capable of telling the computer there is a malfunction? Hint... it ain't the valve itself.

 

[RonD]

What is the EGR Code(s), there are several?

If you unplug the EGR valve's vacuum hose and plug it, does the slight misfire go away, and does it drive OK or better without EGR, it might Ping a bit but other than that?

 

[RangerFabWorks]

Here’s the codes it was throwing. Disconnecting the vacuum in the egr makes no difference

 

[RonD]

11 System checks OK
10 place holder not a code
Memory codes
31 EVP signal is/was out of range
33 EGR did not open/ respond during test or if memory code, did not open intermittently
87 Fuel pump circuit fault (check inertia switch)

I don't see anything that would cause a slight misfire at idle
Because its an emissions system 31 usually means EGR sensor didn't show it was opening(not that it open too far), which is confirmed by code 33, it didn't open when tested or when driving

If you swapped out EGR valve and sensor(EVP) and got the same codes then must be wiring, or connection at EVP or Computer
But shouldn't cause running issues

87 means the Computer didn't see the 12volts from Fuel Pump relay closing and sending 12v to fuel pump on pin 8, if engine is running then erroneous code, may have been set during other testing if you pulled FP relay or fuse

Computer and wiring is sneaking up on 30 years old, you could pop the top on computer and have a look at the capacitors, and the circuit board in general

A working EFI is way more reliable and better running than the best carb setup, but key word is "working" EFI
And 1991 is old enough to consider the carb swap vs chasing 30 year old wiring issues, lol
The 302(5.0l) stuff is not all that expensive

 

[RangerFabWorks]

Those were the codes before swapping the egr.
After swapping the egr. I got codes. 11. 18. And 87. 18 I believe was from me adjusting the timing and forgetting to unplug the spout. The egr codes did not reappear.

Tomorrow I will go over the plugs and wires again just to make sure I didn’t screw something up

 

[RonD]

What spark plug gap are you running?
And is it stock distributor and coil
Or is it Coil Packs in 1991?

 

[RangerFabWorks]

What spark plug gap are you running?
And is it stock distributor and coil
Or is it Coil Packs in 1991?

.45. And stock distributor. With accel cap and rotor. And airtex replacement coil

 

[RonD]

Sound good, I see some using .054 gaps on regular coils which I think is too much, its OK for coil packs but not the distributor setups

 

[PetroleumJunkie412]

Speed density > everything else.

Fight me.

 

[adsm08]

I agree with PJ. Speed/Density has limitations, but it is less sensitive to air leaks than MAF.

 

[RangerFabWorks]

Speed density > everything else.

Fight me.

dirtmans basement?

 

[PetroleumJunkie412]

dirtmans basement?

YES.

I agree with PJ. Speed/Density has limitations, but it is less sensitive to air leaks than MAF.

Yup. Though, MAP/MAF blend is still king.

MicroSquirt® MAF and MAF/MAP Blend

 

[franklin2]

Don't forget the solenoid that controls the EGR. It's what the computer uses to apply vacuum to the EGR valve. It's usually mounted over on the pass side fender. And it has a foam filter under a plastic cap that gets dirty and is never cleaned. When the valve blocks vacuum to the EGR and wants it to close, it has to let air into the line so the EGR will close. This air comes through the valve through that foam filter. Here's a picture.

 

[rusty ol ranger]

Does it idle smoothly in drive?

Every older EFI ford ive had has a bit of a "tremor" idleing in park.