MAF question
07-25-17, 12:19 PM
#1
Rotary Freak
Thread Starter
MAF question
Symptoms:
When car starts (from cold), it immediately dies. Thinking it was the MAF sensor, I jumpered the fuel pump check connector and found the problem unchanged. Then my next thought was that it was the coolant temp sensor on the back of the thermostat housing that had failed, so I wasn't getting any warmup enrichment. But even with my foot trying to keep it running, it would die. After several attempts to start it, it will begin to run (but rough, and only with my foot on the pedal) smoothing out as it warms up. Once warm, it will idle normally, however when the throttle is applied it will break up heavily until about 3000 RPM, and won't rev any higher.
These symptoms manifested this morning, but yesterday and the day before I was having issues as it seemed the secondary injectors weren't firing (gutless above 4000 RPM). Fuel pump is brand new (Denso), as is the fuel sock and fuel filter. Inside of the tank is squeaky clean. TPS is adjusted properly, no dead spots. Plugs are clean, coils are all firing evenly.
Question:
I took both of my MAF sensors and checked them as per the FSM, and they both check out fine. They do not however, transition smoothly as the flapper door opens and closes. Measuring between the pins E1 and FC, there are lots of little leaps and drops in resistance as the door transitions from open to closed. The FSM doesn't actually ask you to test this though, so I'm not sure if that is the way it is supposed to be.
Does the resistance move smoothly (as it logically should) in a working MAF, or is this normal?
And if it is normal, what else could be causing this?
When car starts (from cold), it immediately dies. Thinking it was the MAF sensor, I jumpered the fuel pump check connector and found the problem unchanged. Then my next thought was that it was the coolant temp sensor on the back of the thermostat housing that had failed, so I wasn't getting any warmup enrichment. But even with my foot trying to keep it running, it would die. After several attempts to start it, it will begin to run (but rough, and only with my foot on the pedal) smoothing out as it warms up. Once warm, it will idle normally, however when the throttle is applied it will break up heavily until about 3000 RPM, and won't rev any higher.
These symptoms manifested this morning, but yesterday and the day before I was having issues as it seemed the secondary injectors weren't firing (gutless above 4000 RPM). Fuel pump is brand new (Denso), as is the fuel sock and fuel filter. Inside of the tank is squeaky clean. TPS is adjusted properly, no dead spots. Plugs are clean, coils are all firing evenly.
Question:
I took both of my MAF sensors and checked them as per the FSM, and they both check out fine. They do not however, transition smoothly as the flapper door opens and closes. Measuring between the pins E1 and FC, there are lots of little leaps and drops in resistance as the door transitions from open to closed. The FSM doesn't actually ask you to test this though, so I'm not sure if that is the way it is supposed to be.
Does the resistance move smoothly (as it logically should) in a working MAF, or is this normal?
And if it is normal, what else could be causing this?
07-25-17, 11:51 PM
#5
Rotary Freak
Thread Starter
No it isn't, and yes a few months ago it was tested 100PSI on all faces.
MAF tested fine, will provide the link below for future reference.
There has been a development. This evening after testing one of the MAF sensors I installed it as my car (as it is now known good) and the reset the TPS (had removed it to test) and the car drove fine. No break ups, pulls strong right up to redline. Secondaries fired fine.
Then I went inside, ate dinner, and came back out to drive to a friend's place and the car started and idled fine, but my symptoms have come back. Break up until 3000, won't rev higher than that.
Found the way to test the MAF in this thread on NoPistons:
https://www.nopistons.com/2nd-genera...er-check-1495/
MAF tested fine, will provide the link below for future reference.
There has been a development. This evening after testing one of the MAF sensors I installed it as my car (as it is now known good) and the reset the TPS (had removed it to test) and the car drove fine. No break ups, pulls strong right up to redline. Secondaries fired fine.
Then I went inside, ate dinner, and came back out to drive to a friend's place and the car started and idled fine, but my symptoms have come back. Break up until 3000, won't rev higher than that.
Found the way to test the MAF in this thread on NoPistons:
https://www.nopistons.com/2nd-genera...er-check-1495/
07-25-17, 11:54 PM
#6
Rotary Freak
Thread Starter
Sorry, it would have been a good idea to include that.
1986 N/A, manufacture date 01/10/85.
I include the manufacture date as I know the early FCs had little differences from the newer ones.
Also, I should note that there are no mods excluding removal of pre-cats and replacement with pipe, and aftermarket catback. Main cat in place. No idea if any porting was done, as I was not the one who built this engine.
1986 N/A, manufacture date 01/10/85.
I include the manufacture date as I know the early FCs had little differences from the newer ones.
Also, I should note that there are no mods excluding removal of pre-cats and replacement with pipe, and aftermarket catback. Main cat in place. No idea if any porting was done, as I was not the one who built this engine.
07-26-17, 12:09 AM
#7
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just tossing it out there..
do you have that Tube running off the bottom of the TB snorkel hooked up to the steel tube on the engine?.If not massive vacuum leak.
do you have that Tube running off the bottom of the TB snorkel hooked up to the steel tube on the engine?.If not massive vacuum leak.
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07-26-17, 12:14 AM
#8
Rotary Freak
Thread Starter
Tube is connected. It's worth noting that a month or so ago I redid the entire intake with new fuel hoses and new silicone vacuum lines, as well as testing all of the solenoids on the vacuum spider. The car was fine until this started happening a few days ago (except for a fuel pump failure, which has been replaced). Injectors were rebuilt last October.
07-30-17, 11:49 PM
#9
Rotary Freak
Thread Starter
Final Update
Just thought I should leave the solution to the problem in case someone has similar symptoms.
I removed the ignition coils (leading and trailing) to test the coil resistance. After checking the resistance, which was in spec, I cleaned the terminals and put some dielectric grease on them. Then I cleaned the region of metal around the studs that hold the coils in place and did the same for the place where the coil brackets mount to the body. I don't know if the coils ground out through the casing, but it seemed like a good idea.
Problem is completely gone. I've been driving it for two days without issue.
I removed the ignition coils (leading and trailing) to test the coil resistance. After checking the resistance, which was in spec, I cleaned the terminals and put some dielectric grease on them. Then I cleaned the region of metal around the studs that hold the coils in place and did the same for the place where the coil brackets mount to the body. I don't know if the coils ground out through the casing, but it seemed like a good idea.
Problem is completely gone. I've been driving it for two days without issue.
07-31-17, 07:24 AM
#11
Just thought I should leave the solution to the problem in case someone has similar symptoms.
I removed the ignition coils (leading and trailing) to test the coil resistance. After checking the resistance, which was in spec, I cleaned the terminals and put some dielectric grease on them. Then I cleaned the region of metal around the studs that hold the coils in place and did the same for the place where the coil brackets mount to the body. I don't know if the coils ground out through the casing, but it seemed like a good idea.
Problem is completely gone. I've been driving it for two days without issue.
I removed the ignition coils (leading and trailing) to test the coil resistance. After checking the resistance, which was in spec, I cleaned the terminals and put some dielectric grease on them. Then I cleaned the region of metal around the studs that hold the coils in place and did the same for the place where the coil brackets mount to the body. I don't know if the coils ground out through the casing, but it seemed like a good idea.
Problem is completely gone. I've been driving it for two days without issue.