12/17/2023 0 Comments Ignition timing advanceI took it for an extended test drive with the monitors hooked up and recording, and there seems to be a fairly firm correlation between engine speed and air flow. I've read that it's calculated based on the MAF, but that doesn't sound right. The problem with using engine load to calculate the timing advance is that engine load is itself a calculated value. I'll check the flywheel position sensor this evening when I get home, thanks for the advice. I was leaning that direction because it way up at the top of the engine and really easy to get to. I'm slowly coming to accept the fact that the problem is NOT with my TPS. I still think I'm leaving out a bunch of info. There's just so much info to consider, it's hard to ask a question without giving background. Thanks in advance for your help, and sorry about the long post. Not as good as I'd expect, but nothing crazy that would indicate a really bad sensor, and certainly nothing that would cause a 50% drop in timing advance at 30% throttle (adjusted, so that's really 30% throttle). Does anyone know what inputs the PCM uses to calculate timing advance? I'm suspecting my MAF sensor, but it has a reasonable correlation with RPM. It looks like the PCM is showing absolute values instead of adjusting for actual range.įinally, here's my question. 4.97 = 93.3%, which is what my TPS reads at WOT. 1.00 / 4.97 is 20.3%, which is what my TPS reads at idle. At idle (ignition on, engine off) I get 1.00 volts and at WOT I get 4.77 volts. I tested the voltages on the TPS both at the sensor and at the PCM. This is what I would expect since I'm opening the butterfly on the throttle body and letting more air in. If I press the accelerator, air flow increases. Engine load is supposedly calculated based on air flow divided by peak air flow, but there's a reasonable correlation between throttle position and air flow readings. The diagnostics also shows crazy numbers for my engine load and short term fuel trim. Either the PCM is bad or (more likely) it's getting a bad input from something and is trying to compensate. This explains the very poor acceleration, but since the ignition timing is controlled by the PCM there's nothing to adjust. Gentle acceleration actually works, but when I start to press the pedal a little I immediately notice the timing advance drop from 20-30 down to around 5-10. I took it out on the road and recorded all parameters under various conditions. I immediately suspected by TPS, and being only $20 I replaced it. This seems a little weird, so I plugged the computer into my wife's truck for comparison and her TPS shows 0% when you're not pushing the pedal and 100% at WOT. Sitting in the driveway, my TPS reads 20.4%. If I saw the problem, I'd have fixed it already. Ok, I didn't see the problem, but I saw the manifestations of the problem. I plugged in my computer and immediately saw the problem. Unfortunately, it's not any single cylinder, and it's even tossed up a P0300 (Random misfire) a time or two. By bad performance I mean that power goes to almost zero, the car stutters, bogs down, jolts and starts throwing up cylinder misfire trouble codes. The problem I'm experiencing is very bad performance on acceleration. I can't find a button that says "Skip all this technical stuff and just tell me what's wrong with my car" so I'll have to do it the hard way and think a little. Since the whole car is computer controlled, and trouble codes can only tell you so much, I got a PCM interface and software to talk to the PCM from my laptop. My 2000 plain-no-frills-out-of-the-box Focus went from a great car to a lemon in a very short time. I'm at my wit's end on this one, and from reading some of these threads you guys really seem to know what you're talking about.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |