OK some of you may have been following the ignition thread(s) of late. I borrowed a digital scope from work over the weekend and had a look under the hood. Basically nothing seems out of line although there are some signals that have glitches in them that may/may not be causing problems. Also learned that an MSD-6A sparks 6-7 times at idle.

Anyways here's the pics.

Leading coil at idle (trigger signal vs coil volts vs plug cable)

 

Pic 2: Leading coil at about 3k RPMs

 

Here's one of the plug cables for L1 and L2. You can see that they're completely inverse of each other. ie they both fire at the same time but one goes +ve, the other -ve.

 

This one shows L1 vs T1 vs T2. You can see the delayed T1 (or T2) near the 4th hit on L1 (this is the 15deg diff between the leading/trailing timing). The second set of L1 now has T2 (or T1) firing, showing how they alternate on each L1.

 

CAS signals at idle. This is where I saw some noise that may be a problem (I've seenmy timing jump when using a timing gun, usually retarding about 15-20deg).

 

Here's the CAs at about 4-5k RPM's. Cleaner signal but still one glitch. Don't know how important this is or not...

 

Ever wonder what your TPS signal looks like? Well here it is at idle. Pretty ugly...

 

Here's the AFM 'flapper door output' at idle. Also pretty noisy.

 

OK last one,. This one is the alternator at idle.

 

So what's the summary. Well I'm convinced that the coils are firing. Not sure if the glitches on the signals are causing grief or not though...

Henrik
87TII

 

Wow, that's some serious work!&nbsp Do you mine if I "borrow" those pics and put them up on my website?




-Ted

 

thats pretty cool! what are you tring to fix?? the tps and afm signals look like they could be better, something like that might cause a wierd idle

mike

 

Wow, what a cool thread Definately gotta archive this one.

 

I'm chasing an intermittent loss of power problem. Some days the car has noticeably more punch in the low end than others. Response above about 4k or so (where the ECU goes open loop) seems to be the same either way. akageals has something similar happening. I thought it was ignition related but am pretty sure its not now since I can explain what I've been seeing on the timing light now. Next time I'll check the other input sensors and I think I'm going to try to clean up the AFM and TPS signals. Besides the 'geer in me wants to know how the thing works as well The MSD6A operation surprised me, I thought they topped out at 3 sparks.

Feel free to post the pics where you want - the info is free for all. If you're interested in other signals, let me know, the scope works quite well although the pics are a bit of a pita as the scope saves in eXcel format (of course then I also have 10,000 point traces to do math on!). If you want the raw eXcel files pm me (its about 20megs in total)

Other suggestions for potential sources of the problem are also welcome!

Henrik
87TII

 

Henrik- Thank you for doing this!

I recently timed two NA's, a 90 and a 91. It really bothered me that the L2 signal did not yield the 5ATC mark as the L1 signal did.

All other direct fire/wasted spark setups I have seen have yielded the same view whether the timing light inductive pickup was on L1 or L2. (3rd gen and 1st gen set up direct fire/wasted spark on the leading)

It REALLY bothered me that the 2nd gen leading coil, which is a single primary, dual secondary, could possibly be putting out alternate spark timing.

Apparently the signal inversion must be triggering my inductive light at the wrong time?

Again, thanks for taking the time to give real scientific information!

 

Hullo, Henrik. Power loss below 4000. Just driving along and feel a mild loss in power? Might come and go? I've seen this on my car, the n/a.

I got STUPID, and wondered how a gallon of denatured alchohol mixed with three gallons of gasoline would effect my car. Pure DUMMY idea.Got the germ of a thought from reading emissions tricks done by other people.

First of all I have a 87 and rigged two bug lights on the dash to show fault codes when and if they happen. Well sure enough the car ran like ....well not so good. And one thing that happened repeatedly was the 02 fault code showed up every couple of miles. When the 02 code showed up, the car felt like I'd lifted the pedal up just a bit. If I got back on it hard the 02 fault would disappear for a while. Then come back. Feels just like a power loss or the pedal being lifted up a touch.

I woke up smarter the next day and filled up the tank with gasoline and that self induced problem went away. So I'm saying maybe the 02 sensor is taking a dump on you intermittently while driving.

 

I found that my Crank Angle Sensor had CHIPPED teeth, and was very dirty under the cap.

Please check that ans let us know if that was it.

It may also be the AFM, but thats unlikely.

 

back from ancient history I see... Unfortunately I haven't had time to chase the problem more. Right now it feels great but that's most likely 'cause I just got it back from being dent-free'd and painted (almost 6 weeks in the shop) and have been driving my wifes '85 Tercel during that time. I'm thinking one of the sensors is not functioning correctly, likely affecting the A/F mixture but have yet to track it down. I have a new(er) AFM to try, hopefully this weekend. The O2 sensor is new and does function (I have checked that the ECU goes closed loop when cruising).

Symptoms are when its running not so good are:
- idle quality is worse, a little bit of bouncing around 750, say +/- 50 rpm or so max
- there's a little bit of popping in the exhaust at idle every few secs or so
- throttle response and boost build is slower below say 3-4k
- clutch out and let the engine drop to idle from 3k or so and it falls with a vroom-vroom, stops briefly at about 1k and then drops to 750rpm's

when running good:
- idle is rock steady with no exhaust popping
- throttle response and boost is near instantaneous (breaks loose the rear at part throttle in 2nd if the roads even a bit wet)
- clutch out and let the engine drop to idle it falls steady and smooth right to 750rpm's.

In either case, above 3-4k rpm's there doesn't seem to be a difference. It also seems to be 'selected' when started, ie if its going to run well, it will do so for the whole trip, likewise for the not so well.

Any ideas???

Henrik
87TII

 

Jeesh this sounds like a run-of-the-mill throttle position sensor problem.

Have you adjusted that?

 

Does it seem to be heat related in any way? My daily driver N/A had 199k miles on the original engine... but it does the same thing! I always atributed it to one of 2 things. Ists just getting wore out. or #2; Mine seems to perform MUCH better when its cold, or semi cold. I feel alot more power, a much more steady idle & smother acceleration when its not totaly warmed up. I assumed maybe my car runs a little lean at high temp .. and runs a bit rich when its cold (electric choke type of mixture) Have you got a good A/F meter? can you notice a visable change in the mixture when you see these symtoms?

I can drive my N/A for miles on the highway and keep my full power.. but if I pull off the freeway and sit in trafic a while ... I get my "shitty power" syndrome. I have heard of heat soak .. but this is a N/A and my temp gauge is never aboue 1/4 or so.

 

 

 

Is that a new TPS? - yowza