robertsthebruce

1990 d16a6 engine with all oem parts except for a skunk cam gear. I'm pretty sure the shaft is still oem- it's shiny steel, not iron.

The car was running but had a hunting idle, bad gas mileage and a trouble code 14. I cleaned the EACV, tested the tps. Started it back up and found that disconnecting the injector and spark plug wire to piston 1 made no difference. Checked the compression. 1 was a bit lower than 2 and 3, but 4 was very low, which was a surprise because disconnecting the injector on 4 majorly affected the idle. I relashed the valves. They were a bit off but not much. Tried to start it back up to do a fuel pressure check and it turned over but wouldn't fire. I hadn't disconnected the distributor when checking compression, so I was sure I'd fried the coil.

However...It's still getting a really strong and seemingly correctly timed spark. I tested the ignition coil and got .5 ohms on the a-b connection on the coil and 10,000 something on the a to secondary winding, both of which are within the shop manual specifications. I tested the ICM, and got proper voltage everywhere but found no continuity on the white and blue wires. But I looked on the forums and folks said the ohms test for the ICM is wrong in the manual. I noticed a trouble code 8 at some point, so I tested continuity on the 8p connector to the distributor and found 365 ohms between prongs a and b. There wasn't continuity to the ground from either prong, so I checked the same connection at the main wire harness, at the connector by the fuse box and got 367 ohms there. I don't have an extra ECU to test, but I'm not even sure I'm on the right trail and I'm doubtful that it's the ECU since the car ran just a few days ago. It has new plugs. I've redone every ground very thoroughly. I resoldered and then just replaced the main relay. I tested the ignition switch and it seems to be fine...everything that's supposed to switch on at I II and III does switch on.

It's getting fuel, though I'm not sure how to test the pressure because it won't start. It also won't catch with starter fluid. The fuel pump runs, the injectors are clicking and the spark plugs are wet.

I'm confused by the skunk gear, because the distributor rotor seems to be extremely far advanced when the gear is adjusted at 0, even though the gear appears to be correctly lined up with the crankshaft. I readjusted it so the rotor points right at 1 at tdc. Regardless, it doesn't seem like this is the main issue, since again, the car was running a few days ago.

Where should I go from here?

4drEF

Disconnecting plug 1 and having little effect on idle seems like a clue to me.
(I assume you took ALL 4 plugs out before trying to compression test rather than removing one, doing test, and replacing for each individual cylinder.)
Your compression wasn't low so I'm thinking you have an weak spark issue on that cylinder.

robertsthebruce

Thanks guys.

What baffles me is that it was starting reliably, every time, in every temperature, for months. The issue was the idle, not that it wouldn't start. The thing I did between it starting and not starting was the compression test. The likely explanation would seem to be that I fried the coil during the compression test.

I did take all the plugs out during the compression test, but I didn't completely disconnect the distributor, which is what I'm concerned about. However, The spark on all cylinders is strong, bright white and consistent. It seems like one of the only things left to do is to throw a new coil and ICM at it to make doubly sure, even though they tested fine...

I did make sure all the distributor wires were correct and had correct ohms; that was the protocol I found for addressing the tdc sensor trouble code.

I haven't checked the timing with a timing light, but the car was running, I haven't changed the timing, and the marks, rotor and valves are all where they're supposed to be as far as I can tell; rotor points to 1 at TDC (though it seems too far advanced when the adjustable gear is at 0), valves are closed, and markings on the gear show it being where it's supposed to be. Consequently, the timing may be an idling issue, but I find it hard to believe that it's the reason it isn't firing at all. Never the less, I will also go buy a timing light and check that properly.

4drEF

Performing an resistance (OHM) test on the coil will tell you right away if it's under performing.
It is literally a couple of VERY long wires so there isn't any black magic going on in there.

Coil supplies all 4 plugs with spark so if one wire is sparking better than another, it's likely the plug wire or the distributor cap/rotor. You can resistance check the plug wires to nearly rule them out. Sometimes the insulation on the wires goes bad and spark leak through them - you get all kinds of ignition misses when that happens.


Fixing the TDC code should be your priority. Europhrex is right on the money with this.
Check your distributor wiring and if it's all good, then try a new distributor.
Among other things, the distributor tells your coil and injectors when to fire. If it doesn't know the rotation of the engine, it will refuse to fire or fire at the wrong time.

robertsthebruce

I don't have an extra distributor to try, and it's kind of an expensive part to just throw at a car even though every test I've done on it indicates that it's fine.

To reiterate: OHM test on the coil is good: .5 between A and B and 12,000 between A and the tower. The spark plug wires are all sparking the same (very strong looking white spark with consistent timing) and have no resistance. Wires between the distributor and the ECU have no resistance except for the wires communicating top dead center position between the ECU and distributor, which have the resistance the manual says they should (365). The ICM has voltage where it's supposed to but resistance on the two that the manual says to check for resistance. Online forums say the manual is wrong; can anyone clear this up?

Cap and rotor look great- no corrosion. As I said, I am unsure about where precisely the rotor should be pointing but as the car started and ran before and I haven't changed the position of the rotor or cam it seems unlikely that this would be the cause of the "no "start" or trouble code 8. In fact, the trouble code 8 has not returned so it seems likely that the code is simply due to me disconnecting and testing wires.

I don't have the money to just throw parts at this car and see if they stick, and I already bought a new relay thinking I had thoroughly traced the problem there. I want to make sure I know exactly what should be happening and have diagnosed this as thoroughly as I can before just buying another expensive part. What else can I check? Is the manual wrong about the ICM test and is there a corrected test I can do?

Euphorex

Does the fuel pump even prime? I would go through everything like, spark, fuel, mechanical timing, then see where that leads you.

robertsthebruce

The fuel pump does prime, there is pressure at the filter and the injectors are firing. Here is what I can see about the mechanical timing: At TDC all valves on cylinder 1 are closed and properly lashed. Depending on how I adjust the adjustable gear the rotor is either pointing directly at the #1 post or advanced enough that the trailing edge of the rotor is just barely touching the post as it's moving on to post 3, which is how it's been set since I got the car. I haven't actually timed it with a timing light but again, the timing as it is has never been a no start issue before and I haven't changed the timing. What justification do I have for thinking that the timing is suddenly the reason it won't fire?

4drEF

If you are throwing trouble code 8, then it is a very strong indicator that your distributor is NOT fine.
TDC sensor is not a serviceable component so your distributor must be replaced (assuming all your wiring from TDC sensor to ECU is good).

robertsthebruce

And there's no reason it would be throwing a code 8 because of all the disconnecting and testing and repositioning the rotor with the adjustable gear I've been doing? The code did not happen for over a week after the no start problem started and it hasn't appeared again. The protocol I found for responding to code 8 didn't say I could replace the TDC sensor, but it did have me specifically test the ohms of the sensor and it had a very specific range of resistance that it said indicated that the sensor was working...is this wrong? I'm not trying to be unnecessarily difficult here- I really just don't want to throw more parts at this car without being as sure as I can be of my diagnosis.

4drEF

My understanding was that you had a constant 8 through all this.
Mistaken I guess.

robertsthebruce

Sorry I didn't communicate that bit very clearly. I started working on the car because of poor idle and code 14. I am now just trying to get it to start. There haven't been any trouble codes since it stopped firing except for a brief appearance of 8, which hasn't come back since I tested all the related wires and fuses...

Euphorex

Get a stock cam gear and go from there. Try starting it with full throttle. Get some air in the engine. Otherwise, I don't think I can help anymore. When I had this problem, my engine was out of time.

Euphorex

put it back to 0, see what that does

robertsthebruce

Thanks- I'm going to time it with a light but if that doesn't solve it I'll probably just get rid of it...the car isn't worth throwing more money at for me right now.

cast.aluminum

I'm having a similar problem. My car drove good for a good while. I've just rebuilt it like 8-9 months ago, and, took it for some spirited canyon driving. Work good and then had a weird hiccup where the motor bogged out and started during down but downshifted and turned right back on. Checked compression. And speed 60 psi all across.. do in kinda interested to see your solution (^～^)