What's next (idle and running issues)
09-12-2019, 09:02 AM
#1
Rennlist Member
Thread Starter
What's next (idle and running issues)
Morning everyone,
Hope your day is going well.
MY 1981, 5-speed 4.5L bit of awesomeness.
Started and ran well before work commenced.
Completed a top end refresh and new plugs but nothing on the front of the engine or other ignition system components.
The top end refresh included all new fuel and vacuum lines. Cleaned all parts including the throttle body. Set both micro-switches to spec in the manual. Cleaned the MAF and removed the top to verify operation. All ignition parts were inspected for wear and damage -- normal wear seen yet parts (rotor, cap and wires) still serviceable.
Starts fine now but stumbles after starting, idle is erratic and power is slow. A persistent miss is present now and affects the entire power range.
working my way through the list of possible causes and am running out of ideas. here are results of my investigations.
Fuel pressure is 2.4-2.5 bar running and 1.6 bar after an hour resting (ignition off)
I checked the static values for the MAF but am not able to find specs for a 5-pin MAF connection. My copy of the WSM does not have the pin out specs (shows the 6-pin connector but not the 5-pin). The wiring diagram does show the proper pinout but not the expected values. Where is the 5-pin connector values shown?
The schematic for the MAF appears to be a simple voltage divider circuit wit the following attributes:
Pin 4 is common
Pin 1 is the wiper of the variable resistor
Pin 2 is low side connection of the top of the network (possibly low side of the reference voltage)
Pin 3 is high side connection of the top of the network (possibly high side of the reference voltage)
Pin 5 is low point of the divider network.
Pin 4 connection appears to hold the divider network above zero so the wiper varies from this point to some voltage present at pin 2 (set by the resistor across pins 2 to 3). Is this reading correct?
In effect the only voltage that changes is the voltage present at pin 1. All other pins are static voltages.
Do these values appear 'normal'
meter set on 2K Ohm
Lead number is meter negative lead
1-2--567=>567
1-3--369=>369
1-4--84=>1068=>1335=>399
1-5--1663=>1663
2-3--204=>204
2-4--490=>1309=>900=>249
2-5--2300=>2300 (on 20K range)
3-4--296=>826=>1100=>48
3-5--2020=>2020=> (on 20K range)
4-5--1735=>3000=>2000
I need help in what to look at next before taking it to a shop with proper equipment and incurring the expense. What else am I able to check using home test equipment?
Hope your day is going well.
MY 1981, 5-speed 4.5L bit of awesomeness.
Started and ran well before work commenced.
Completed a top end refresh and new plugs but nothing on the front of the engine or other ignition system components.
The top end refresh included all new fuel and vacuum lines. Cleaned all parts including the throttle body. Set both micro-switches to spec in the manual. Cleaned the MAF and removed the top to verify operation. All ignition parts were inspected for wear and damage -- normal wear seen yet parts (rotor, cap and wires) still serviceable.
Starts fine now but stumbles after starting, idle is erratic and power is slow. A persistent miss is present now and affects the entire power range.
working my way through the list of possible causes and am running out of ideas. here are results of my investigations.
Fuel pressure is 2.4-2.5 bar running and 1.6 bar after an hour resting (ignition off)
I checked the static values for the MAF but am not able to find specs for a 5-pin MAF connection. My copy of the WSM does not have the pin out specs (shows the 6-pin connector but not the 5-pin). The wiring diagram does show the proper pinout but not the expected values. Where is the 5-pin connector values shown?
The schematic for the MAF appears to be a simple voltage divider circuit wit the following attributes:
Pin 4 is common
Pin 1 is the wiper of the variable resistor
Pin 2 is low side connection of the top of the network (possibly low side of the reference voltage)
Pin 3 is high side connection of the top of the network (possibly high side of the reference voltage)
Pin 5 is low point of the divider network.
Pin 4 connection appears to hold the divider network above zero so the wiper varies from this point to some voltage present at pin 2 (set by the resistor across pins 2 to 3). Is this reading correct?
In effect the only voltage that changes is the voltage present at pin 1. All other pins are static voltages.
Do these values appear 'normal'
meter set on 2K Ohm
Lead number is meter negative lead
1-2--567=>567
1-3--369=>369
1-4--84=>1068=>1335=>399
1-5--1663=>1663
2-3--204=>204
2-4--490=>1309=>900=>249
2-5--2300=>2300 (on 20K range)
3-4--296=>826=>1100=>48
3-5--2020=>2020=> (on 20K range)
4-5--1735=>3000=>2000
I need help in what to look at next before taking it to a shop with proper equipment and incurring the expense. What else am I able to check using home test equipment?
09-12-2019, 09:26 AM
#2
Race Car
Do you another known-good MAF to swap in?
09-12-2019, 06:45 PM
#4
Rennlist Member
First a bit of a nit, then some questions.
You have an "AFM" (air flow meter), not an MAF (mass air flow meter). Your air is measured by the "barn door" flap moving. The MAF uses a heated wire element.
Anyway, when I first read your conditions I was thinking AFM problem. I can't help you with the five pin measurements, as I've only ever seen the 6-pin. (It's not in the WSM?) If you can swap one out, that would be great, but also carefully check the AFM plug and connector for cleanliness and all pins and sockets are present and accounted for. I had VERY similar conditions to your on an '83, and I was about to swap out the AFM and looked closely and one of the pin-sockets on the plug had backed out of the plug. Fixed that and was good.
How's the green wire looking. In particular the plug ends?
Next, did you mess with the ignition timing at all? Eg., move the distributor hold down bolt? Again, may cause similar conditions if you threw off the timing.
Or if the rotor or the inside of your cap is cracked or damaged. Check those carefully. Does your rotor fit tightly onto the distributor shaft with no movement? (I had one that the little tongue on the inside of rotor had broken, so it was just wobbling around----again similar conditions to yours.)
Vacuum lines all correctly re-installed? Vacuum line hooked up to your dizzy? The label on the underside of your hood can actually be useful.
Double check that the wire from the cap to the coil is tight and fits well. Check for no damage at the coil socket for that wire.
You seem to have good fuel pressure, and fuel is being delivered to the combustion chamber, so I'm gonna guess it is on the L-Jet or ignition side of things.
You have an "AFM" (air flow meter), not an MAF (mass air flow meter). Your air is measured by the "barn door" flap moving. The MAF uses a heated wire element.
Anyway, when I first read your conditions I was thinking AFM problem. I can't help you with the five pin measurements, as I've only ever seen the 6-pin. (It's not in the WSM?) If you can swap one out, that would be great, but also carefully check the AFM plug and connector for cleanliness and all pins and sockets are present and accounted for. I had VERY similar conditions to your on an '83, and I was about to swap out the AFM and looked closely and one of the pin-sockets on the plug had backed out of the plug. Fixed that and was good.
How's the green wire looking. In particular the plug ends?
Next, did you mess with the ignition timing at all? Eg., move the distributor hold down bolt? Again, may cause similar conditions if you threw off the timing.
Or if the rotor or the inside of your cap is cracked or damaged. Check those carefully. Does your rotor fit tightly onto the distributor shaft with no movement? (I had one that the little tongue on the inside of rotor had broken, so it was just wobbling around----again similar conditions to yours.)
Vacuum lines all correctly re-installed? Vacuum line hooked up to your dizzy? The label on the underside of your hood can actually be useful.
Double check that the wire from the cap to the coil is tight and fits well. Check for no damage at the coil socket for that wire.
You seem to have good fuel pressure, and fuel is being delivered to the combustion chamber, so I'm gonna guess it is on the L-Jet or ignition side of things.
09-12-2019, 09:25 PM
#5
Rennlist Member
while idling, unplug the air flow meter. it it runs about the same, its likely that you have a bad afm. (it will run, but it will run really badly with a bad afm.....if i recall correctly, out of range voltages kick the fuel injector brain into a mode that runs the injectors without regard to air flow input.
when you say you cleaned the flow meter, how did you clean it? what you have is a vane device.....conceptually, the barn more or less is the same as a variable voltage switch, and not a wire. Mass Air Flow Sensor cleaner is made for a wire. I'm pretty certain is could do some damage to the wiper surface of the air flow meter if it made it's way through the hole and down onto the wiper surface.
when you say you cleaned the flow meter, how did you clean it? what you have is a vane device.....conceptually, the barn more or less is the same as a variable voltage switch, and not a wire. Mass Air Flow Sensor cleaner is made for a wire. I'm pretty certain is could do some damage to the wiper surface of the air flow meter if it made it's way through the hole and down onto the wiper surface.
