AFM and Idle Issues (With Some Fuel Pump Issues Thrown In)

[KevAndAndi]

I'm not reading if you replaced the temp sensor or not, but if you suspect it at all, replace it. It can cause a lot of problems if it "thinks" you car is colder than it is.

Thanks, Brad. I did replace the temperature sensor. The old one looked like it might have been original, and as it's such an important component, I swapped it out for peace of mind even if it didn't solve the idle problems (which it didn't). As I mentioned before, the really odd thing is that unplugging the temp sensor prevents the extreme RPM dive that I experience a few seconds after starting.

I'll post a summary at some point because this is a lengthy thread, and I hope it can be of assistance to folks in the future. Covers several typical FI problems that new Spider owners encounter.

[bradartigue]

I'm not reading if you replaced the temp sensor or not, but if you suspect it at all, replace it. It can cause a lot of problems if it "thinks" you car is colder than it is.

Thanks, Brad. I did replace the temperature sensor. The old one looked like it might have been original, and as it's such an important component, I swapped it out for peace of mind even if it didn't solve the idle problems (which it didn't). As I mentioned before, the really odd thing is that unplugging the temp sensor prevents the extreme RPM dive that I experience a few seconds after starting.

I'll post a summary at some point because this is a lengthy thread, and I hope it can be of assistance to folks in the future. Covers several typical FI problems that new Spider owners encounter.

It makes sense. The typical failure state of that sensor is "it's really cold" and the injectors come on full blast. The cars do exactly what you describe, run well for a few seconds then drown in the overly rich mixture.

[KevAndAndi]

I'm not reading if you replaced the temp sensor or not, but if you suspect it at all, replace it. It can cause a lot of problems if it "thinks" you car is colder than it is.

Thanks, Brad. I did replace the temperature sensor. The old one looked like it might have been original, and as it's such an important component, I swapped it out for peace of mind even if it didn't solve the idle problems (which it didn't). As I mentioned before, the really odd thing is that unplugging the temp sensor prevents the extreme RPM dive that I experience a few seconds after starting.

I'll post a summary at some point because this is a lengthy thread, and I hope it can be of assistance to folks in the future. Covers several typical FI problems that new Spider owners encounter.

It makes sense. The typical failure state of that sensor is "it's really cold" and the injectors come on full blast. The cars do exactly what you describe, run well for a few seconds then drown in the overly rich mixture.

What would cause my brand new sensor to manifest a failure state? Seems unlikely that it would be defective. Again, near-stall occurs with (old or new) sensor plugged in, and OK idle occurs with (old or new) sensor unplugged. Near-stall with sensor plugged in occurs a few seconds after starting, but idle becomes better after warm-up. After warm-up, though, idle can vary widely.

I guess what I really need to do at this point is install the AFM and see if the problems persist.

[bradartigue]

I don't know, but the condition you describe is consistent with the failure of that sensor. Whether or not it is causing your problem, I have no idea. I would test the wiring to be certain, if it all falls in the right ranges then I'd move on.

[KevAndAndi]

I don't know, but the condition you describe is consistent with the failure of that sensor. Whether or not it is causing your problem, I have no idea. I would test the wiring to be certain, if it all falls in the right ranges then I'd move on.

Thanks. I did test the sensor previously and everything was OK in terms of ranges.

To clarify, I was finding it odd that the engine would run (and run better) with the coolant temperature sensor unplugged. I was under the impression that it would run poorly, or not at all.

Will post results of idling with rebuilt AFM installed once I get some time in the garage.

[lanciahf]

Kevin if the Bosch FI is working properly, disconnecting the FI coolant temperature sensor on a hot engine will richen the mixture and flood the car out.

BTW did you ever do a compression check on the motor?

[KevAndAndi]

Kevin if the Bosch FI is working properly, disconnecting the FI coolant temperature sensor on a hot engine will richen the mixture and flood the car out.

BTW did you ever do a compression check on the motor?

Well, then, I think we can conclude that the Bosch FI was not working properly! Again, I realize that much will be answered once I install the shiny, rebuilt AFM that's sitting on my counter.

I have not yet done a compression test, but a gauge is on my list of things to buy. The engine runs quite well - good and strong - once warm, except for the unpredictable RPM level when we pull up to stoplights.

[spider2081]

The coolant temperature sensor is a variable resistance. At 14 degrees F the sensor measures about 7-11 thousand ohms, at 68 degrees F the sensor reads 2-3 thousand ohms, at 176 degrees F the sensor reads 270-390 ohms. If the wire connection between the sensor and the computer is defective and measures high resistance the computer thinks the sensor is sensing a colder atmosphere than it actually is. Have you measured the sensors resistance from the computers connector. The sensor is connected to pin 13 the other side of sensor is connected to ground. If you disconnect the computer and measure the resistance on pin 13 to ground the the resistance should be between 2000-3000 ohms. If much higher there is a bad connection between sensor and the computer or the sensor is a defective new part.

[lanciahf]

What Dave said!

[sierraspider]

KevinandAndi

I'm the one who recommended FIC. Just curious about your experience with them and if AFM is working properly. Read your thread about Temp sensor being culprit. 'thought I'd check in

[lanciahf]

Also have you checked the valve clearances?

[KevAndAndi]

The coolant temperature sensor is a variable resistance. At 14 degrees F the sensor measures about 7-11 thousand ohms, at 68 degrees F the sensor reads 2-3 thousand ohms, at 176 degrees F the sensor reads 270-390 ohms. If the wire connection between the sensor and the computer is defective and measures high resistance the computer thinks the sensor is sensing a colder atmosphere than it actually is. Have you measured the sensors resistance from the computers connector. The sensor is connected to pin 13 the other side of sensor is connected to ground. If you disconnect the computer and measure the resistance on pin 13 to ground the the resistance should be between 2000-3000 ohms. If much higher there is a bad connection between sensor and the computer or the sensor is a defective new part.

Thanks, I did do the test but will re-check after I get the AFM installed.

[KevAndAndi]

KevinandAndi

I'm the one who recommended FIC. Just curious about your experience with them and if AFM is working properly. Read your thread about Temp sensor being culprit. 'thought I'd check in

Experience was great! They were nice to deal with, cost was reasonable, and it's great to have the peace of mind that the AFM has been made like-new, tested, and adjusted. They even re-plug the air bypass screw to discourage further mischief.

I've been traveling and then working late at the office so haven't had the few minutes necessary to re-install the AFM and fire up the engine. Will post results as soon as I can get to it. If AFM is working as it should, I will be a big Fuel Injection Corp. booster.

[KevAndAndi]

Also have you checked the valve clearances?

No, I haven't yet. It's on the 8-mile-long list. I'm just trying to be as methodical as a somewhat-ADD person can be, at this point making sure that the FI is working properly.

[lanciahf]

I would start with the basics and then tackle the FI system. At least you know where you are starting from.