Misfire... 240 from satan

[mrmarbles]

I've been having nothing but problems with my 240... where to begin.

So I bought the car with a blown motor, swapped out with another KA24DE someone pulled for their swap, and I got the car running perfectly. After about 2 months of driving it, it began running on three cylinders. Cylinder one's injector wasn't firing, so I went ahead and replaced all four injectors. Problem fixed. After a good month of driving, cylinder three was failing. I replaced all ignition parts except for the distributor itself, I replaced the injector again, which fixed it for maybe two days, and it began missing again. The injector will not fire.

I've replaced nearly everything since then with no luck. It is a freshly rebuilt motor, all ignition side is new except the distributor, all brand new injectors, new wiring harness, and I've tried three different ECU's just to rule that out.

What do I need to check? I've run out of ideas. Someone suggested that the ECU wasn't getting the initial signal so that it could pass it on to the injector. As in the ECU has to get the signal from somewhere in order to make the injector fire at the right time, right? Probably a crankshaft or cam sensor? I don't know what else it could be.

The only thing left is an exorcism.

[zachattack_5491]

I don't know much about injectors and stuff, but just to get the ball rolling... are you throwing any trouble codes?

Also, are you positive the injector isn't firing? Is it not getting signal, or is the injector itself just having a problem?
Modified by zachattack_5491 at 11:03 AM 6/15/2009

[mrmarbles]

No engine codes.

The injector is not firing at all. I've checked spark, and its a brand new motor, so I don't have a stuck valve or anything like that. Also, I've pulled the fuel rail and put a little paper towel underneath the injectors, and all but the third cylinder spray fuel.

Funny thing is, we decided to replace the injector last time because we were checking for a fire signal from the ECU to the injector. from the ECU to the end of the plug was perfect. 50ish ohms I think? Once it was plugged into the injector, there was either much more resistance, or no signal at all from the ECU. (I don't remember the details exactly, I wasn't the one that fixed it last.) So the injector was replaced, and it ran fine for about the next three times I drove it. The last time I turned it on, it was on three cylinders... I guess I should check the signal from the ECU again, to see if thats the issue.

[zachattack_5491]

Wow, that just blows my mind lol. I have no idea what the problem could be aside from just really really bad luck with injectors

[mrmarbles]

Hahaha exactly my thought. I've replaced the injector... 3 times? I've gotten pretty good at it. :P

Aaaaand its time for an exorcism. I just need to get my hands on some holy water.

But really, the only thing I haven't replaced is the distributor or the fuel rail. Is there any way those could affect it?

[Wc240]

with ign on, you should have 12 volts on on wire and no noltage and no continuity on the black. injector resistance should be 12 ohms. might wanna look into a noid light. pretty cheap and a sure fire way of testing/diagnosing injectors.also, check your harness for the injectors

[mrmarbles]

I'll test continuity on the injectors as soon as I get a chance. You're saying 12 volts on the positive wire grounded to the chassis? I'll test voltage to the between positive and negative injector wires, as well as from the positive to the chassis, if that makes any kind of a difference. Also, resistance should be checked between positive and negative wires of the injector wires, correct? I'll update as soon as possible with results.

[Wc240]

turn ign on, test votlage from red wire and ground(chassis/neg battery post) the uce grounds the injectors,fast enough that your meter wont catch it. thats why i suggested the noid light.unplug the injector and check resistance across the injector(not the harness)

[mrmarbles]

UPDATE!

I checked voltage between the positive of the injector and the negative on the battery. 13 to 14 point something volts once it finally caught up with the injector. Same result from the positive to the negative of the injector. I also checked ohmage at the injector, which was less than 12 ohms. All beautiful. So the problem was somewhere else. I checked spark, and I have spark.

Big hint number one: After leaving the car on long enough to check the electronics of the injector, the car reeked of unburned gas.

So I decided to see what would happen if I just switched injector 3 with injector 2. I pulled them both out, and as I was about to swap them I noticed something a little off. The seal at the end of the injector was torn up, and the fuel rail was a little off... As in the hole at the end of the fuel rail didn't quite line up with the hole on the intake manifold. This left a pretty big lip between the two holes at cylinder 3, and a slightly smaller lip at cylinder 2. Basically, the fuel rail was not straight, and it was as if the rail bent upwards and set those two cylinders off.

The reason I thought that the injector wasn't firing was because I had spark, and the motor was brand new. The only thing left would be the injector. I was right, but instead of not firing, it was leaking out just enough to not allow spark, and not enough to actually have much gas go through the system to make me think there was a ton of unburnt fuel.

So I'm thinking that i managed to bend the fuel rail when I did the first swap, just enough to slowly eat at the injector seals. Once the injector seals got torn up just enough, there was too much gas leaking in the cylinder to allow any spark. Cylinder 2 was in the same situation, but it wasn't as far off, so it didn't get eaten up as easily.

Also, the reason it is cylinder 3 only, is because the bend is between cylinder 3 and 4. There are two mounting bolts right next to cylinder 4, and on more between cylinders 1 and 2. The mounting design allowed cylinder 4 to sit flush, and cylinder 3 to be off, but the last bolt pushed cylinders 1 and 2 straight enough to work.

This would explain why it went out every time I replaced something in the fuel system, and nothing ever got fixed when I replaced the ignition system. It also explains why just resealing or reseating the injectors fixed the problem temporarily. It even explains why the car began to miss in the first place when I romped on it. More fuel, more pressure, all against an uneven surface... broken injector seal.

Let me know if this makes any sense. Basically this car has made no sense to me so far, and this is the only thing that explains the constant issue.

I'm looking through local forums and craigslist right now for a fuel rail. If you happen to be in San Antonio and have one, let me know. haha