- This topic has 35 replies, 5 voices, and was last updated 10 years, 8 months ago by
.
-
Topic
-
When the engine warms up, it loses ignition advance! It seems that the signal from the cam position sensor is not getting to the computer, so, it defaults to no advance. It doesn’t give a “check engine” light; reading the pre-OBDII codes doesn’t show any faults. I’ve tried a new cam position sensor – no change. I’ve also groomed all the connectors related to the computer & sensors. I suspect a wiring harness issue, although the resistance readings (cold) agree with the factory manual.
Anybody know of favorite places to look for wiring issues? Or have a better diagnosis?
RoyL
-
Replies
-
Or have a better diagnosis?
I vote for this option.
Q: Why do you think ‘it’s losing ignition advance?’ Does the engine bog down under acceleration? It could be a fuel delivery issue. :dry:
Simple check with a timing light. Initially, both the dealer & I thought it was a fuel delivery issue – after swapping injectors with a new one & testing/swapping sensors, I finally thought to check timing. The lack of advance also fits with the occasional “spitting back” thru the intake when it’s warmed up.
RoyL
Seems to be a ECM type of issue… any codes?
If no codes, I would lean more towards a mechanical issue.
No codes, even with the dealer’s special reader. I’ve also tried swapping the ECU with another one – no change.
RoyL
was engine data monitored while the engine was put under acceleration? Is the computer actually ‘seeing’ what it needs to see?
Any one of these can affect driveability; it is possible the ECM may not be commanding an advance in timing because it thinks it’s at idle (when it’s actually not:)
- Fuel injector Pulse Width
- Engine Coolant Temperature
- Engine RPM
- MAP or MAF sensor
- Intake Air Temperature
- Throttle Position
- O2 Sensor
- Short Term/Long Term Fuel Trim
Additionally, you may be able to monitor ‘timing advance’ specifically as you accelerate the engine and see if that is actually the problem.
Here is one related Technical Service Bulletin:
ENGINE – TIMING BELT – S/M REV
TSBID: 8267 Mfg Num: 18-46-98 Issue Date: 1998-04-24If you have a distributor, it’s possible that one of the components, such as the magnetic pickup, centrifugal advance, or Ignition Control Module might be the issue.
Using a timing light, I can see that when it warms up it no longer provides proper ignition advance. Without adequate advance, the engine barely runs. I’ve gone thru all the tests in the service manual – everything is in spec when the engine is cold. I’ve done a few hot checks without finding the problem, not definitive, since I didn’t repeat all the tests hot.
RoyL
Not sure if you have tried this, but have you backprobed the Camshaft Position Sensor while the engine is running and checked what it is putting out at the sensor? Perhaps something with the pickup for the CPS as well….
If it is running in specs, there probably is a wiring problem… May have to chase down the wiring back to the ECU….
-Karl
The camshaft position sensor on that engine is basically just a coil of fine wire! It senses a magnet on the timing pulley by putting out a small voltage as the magnet goes past. It’s a fairly small voltage; when I played around with a spare sensor & a magnet, I was seeing around 0.1 volt. The factory manual calls for an oscilloscope to read the sensor output – they don’t bother to mention anything about what the readings should be, they just show a picture of the expected waveform.
If/when the rain stops, I’ll drag the oscilloscope out to the car to confirm that the sensor is truly putting out a signal when it’s warmed up.
I’ve also taken off the timing belt cover to make sure the cam pulley (which holds the timing magnets) is properly positioned. It is; it’s firmly attached to the camshaft & end float is well within specs. I still think I’ve got a wiring issue, even though it hasn’t shown up with cold checks. I’m going to repeat the whole set of diagnostic checks with a warm engine, after the rain stops & it gets warm enough to not have to wear gloves while trying to do finicky work;-)
RoyL
I’ve heard of where a pre-OBDII car would have a loud motorcycle pull up next to it and the car motor would die. So, wondering if this engine has a knock sensor and if so is there loud valve noise. The engine computers back then weren’t very advanced and would sometimes pull timing at any noise.
There’s no knock sensor on the engine. It has the problem when it’s in my driveway with no other running engines near it.
RoyL
I think you’re way off base on this one. If you’re experiencing a performance problem that would be one thing, but it seems to me that you’ve just gone out and assumed there’s a problem. Manufacturers run more advance at start up normally and back it off when the engine warms up. The Subaru strategy in this case seems to be to go to 0 advance when warm at idle. As you accelerate it may change accordingly. As I said, if you’re not experiencing a performance problem, there likely isn’t a problem. And if there IS a performance problem, it probably is somewhere else and may have nothing to do with ignition timing. On modern vehicles don’t mess with ignition timing. It’s normally controlled by the computer and cannot be altered. Replacing a bunch of sensors to address a perceived problem is not going to be very productive. If you really want to know what’s going on perhaps pick up a service manual for your vehicle and see what the manufacture has to say about it.
The only reason I started looking for a problem is that the car has become undrivable! I’m fully aware that timing is computer controlled on this engine. Since the problem began, about the only way to get the car to move is to use “manual” mode on the tranny to force RPM high enough to get any power. Under 2000 RPM, it barely moves, even in 1st gear.
When the engine is cold (right after starting), it behaves normally. By the time the temp gauge is coming off the peg, it’s beginning to act up; when it’s at normal temp the problem is in full swing. It’s been to the dealer to have the pre-OBDII codes read on the special Subaru code reader – they didn’t find anything. They also tried replacing injectors – no change.
RoyL
Your problem many not be engine performance. It could be a transmission problem by the sound of it. I would recommend you read through these articles before you replace anymore parts. I think it would be beneficial to find the problem first. The answer may be in here.
http://www.ericthecarguy.com/faq/solving-automotive-performance-issues
http://www.ericthecarguy.com/faq/solving-transmission-problems
Good luck and keep us posted.
The transmission is doing exactly what it’s supposed to do when it’s supposed to do it. The only reason I’ve resorted to using the “manual” mode is to force engine RPM higher to get a little performance from the engine. The basic problem is a lack of power when the engine is warmed up. The lack of power seems to be caused by the ignition timing not being advanced as it’s supposed to be. Using a timing light + the occasional “cough” through the intake confirms that there’s a lack of ignition advance. My ignition scope shows no problems in the secondary side; it’s an older unit that’s mystified by a breakerless primary.
In an effort to reduce the number of “try putting it in gear” type of solutions, I’ve done all the logical initial steps after the daughter who usually drives the car complained about it not working properly. It’s got new plugs & wires (which it was overdue for) as well as a new air filter – in other words, a minor tune-up.
FWIW, I’m a BSME who’s been doing auto repair since the late ’60s, worked at a couple of shops that got “tough dogs” sent to them by other shops. This one had me stumped before I took it to the dealer to get the pre-OBDII codes read – that accomplished about nothing except lightening my wallet.
RoyL
Understand that I’m not discounting your mechanical abilities at all. What I am saying is that so far, I don’t see where you’ve listed actual proof that ignition timing is the problem. As I said, these vehicles run different ignition timing strategies for optimum performance and fuel economy. Since the timing is done by the computer, there really is no adjustment. With modern vehicles, ignition timing should not be messed with for this very reason. That said, if the MECHANICAL timing of the engine is off, it can cause all kinds of issues with timing. I myself had an issue with the performance of my own Subaru and it turned out the left cam was a tooth off. I put it back in time correctly, and the performance issue went away.
Your backfire through the intake could also be caused by a lean condition or an ignition misfire. I know you say you have a lot of new parts on the ignition system so you can put that at the bottom of the list, but I will say that with Asian vehicles they can be very sensitive about the parts you use. Some makes really don’t take to ‘cheep’ ignition components. That said, a vacuum leak can also cause a lean condition and performance issues.
My point is that I don’t subscribe to your theory that the ignition timing is the issue. I think it’s more likely there is some other cause we haven’t explored yet. Perhaps an exhaust restriction which is easy enough to check for.
I could be wrong about the timing, but I don’t think so. Perhaps theres an issue with the igniter or something like that, but so far I don’t think we have any proof of that. Looking at the primary waveform would help make that determination. Please keep us posted on your progress.
- You must be logged in to reply to this topic.