Hot Start Cylinder Misfire

[wannaeatyourbrains]

Oh, it's only happening hot. That's the difficulty. Don't give up but. Just gotta be patient. you will be so stoked when you nail it.

 

[high_point]

did a little bit of testing tonight, drove the car around for a bit then parked it back at home.

Still started fine immediately after the drive. Left it for 15 minutes and came back. Misfire. Cylinder 5.

As i'm pretty hooked on it still being a wiring/ecu heat issue, decided to disconnect the ecu and blow some aerosol duster turned upside down over the ECU Pins/body to cool it down.

Reconnected the ecu, misfire disappeared.

Now this could be just coincidence, but ran out of aerosol duster before i could try some more tests. but from what i can tell the connection between the ecu and harness would seem to be the issue here.

Whats really throwing me is why it has moved from cylinder 3 to cylinder 5, and not sure if i might make it worse with this extreme heat cycling.

Doesn't quite tell me if the issue is with the Pins to the ECU or if its with the contact between the pins and the harness. But think i'm getting somewhere. Might try disassembling the harness side of the connector on the weekend to take a look at the pins there, see if there's anything obvious.

And just a note on the gas injectors you mentioned, they don't kick in until a minute after the car starts, car always runs on petrol to start with.

 

[Fu Manchu]

Have you checked you got sparks coming from your coil packs, and your injectors are firing? I reckon I would be checking that first. You can see if the coil packs are firing if you get someone to turn your motor over for you. I don't know about LPG injectors but it is easy to see if regular ones are working. You can see if you got power to the injector plugs with a test light or LED from a kid's toy. That would narrow things down for you.

The computer is robust, but you can get them tested and repaired, cause misfire is one common issue. I had the one in my car tested by Kevin Stigant in Perth, who is a good guy.

He has helped me out before. Great guy.

 

[Fu Manchu]

Have you bought and installed eBay spark plugs. the market is flooded with fakes of all major brands. Hard to tell the difference.

Also, relative to your investigating so far, have a watch of this which identifies a similar problem. Not the exact fault but the theme of the fault. Loose connection at temperature only.

 

[high_point]

Haven't installed the plugs recently, mechanic said they were all in good nick when i took it in to get diagnosed and confirmed the coils were all in working order.

Bought a ECM set from a wreckers to see if that would fix the issue, installed and the car starts and runs as per usual, but i'm still having the hot start issue.

And looks like it gotten worse.

Car cranks but struggles to start, can get it to turnover by pushing in the throttle, it'll start up but now its throwing a bunch of injector codes when hot and won't idle, dies when it drops below 1000 RPM.

currently throwing the following codes.
P0300 - multiple misfire
P0305 - cylinder 5 misfire
P0303 - cylinder 3 misfire
P0205 - injector 5 circuit malfunction
P0273 - injector 5 - circuit low

Wonder now if maybe some of the wiring is starting to give up, just seems strange that it would only happen when its hot.
might try giving the delphi connector a cool down too just to rule that out.

chances are maybe i did fix the cylinder 3 issue for good and now this is another issue.

might have to run through coils/plugs/injectors again, and super unfortunate for it to trigger a couple of weeks after being checked at the mechanic.

 

[wannaeatyourbrains]

Well, you got some good clues right there. Definitely something wrong with the operation of injector 5. The wiring, the connector, or maybe the injector itself, seeing as it is only happening when it is hot. Not too optimistic cylinder 3 misfire is fixed but, ha ha. You were poking at your harness with a pin and stuff too, right? And now injector 5 doesn't like it.

Cause you already changed the coil and plug for three already, it is probably the injector giving you grief there, too. The other guy was saying that the wiring for gas injectors causes issues. I don't know about gas injectors in particular, but if it requires fitting new connectors, there is a place for the car to be temperamental for sure. Sounds like a good clue.

I reckon focus on making sure the injectors, the connectors and their immediate wiring are all good.

It is the little things get you. I have had wiring issues myself the last few weeks. I am rebuilding a Trailblazer. Got everything finished, then it had a slight misfire. With no codes. After going through everything, I finally found the spark plug tube seals had the slightest leak and that stuff being blown into them was shorting the spark. Then the airbag, ABS and traction control lights came on. Tech 2 said Rollover Sensor and right front wheel speed sensor. Well, after pulling all the seats and carpet, dash and console out, could I find anything wrong with the Rollover Sensor? No. So I moved onto the wheel speed sensor. Tested that and the connections, swapped right for left, blah blah blah. In the end, I discovered that when I did the engine mounts, I crimped the wire for the sensor behind the mount for the rubber mount that attaches to the chassis. Fixed that, and the airbag light went off with the others...

The majority of pain is self-inflicted.

 

[high_point]

So since been in lockdown I've managed to have a good crack at diagnosing the issue, and seem to have found it.

As suggested previously, looks to be a wiring issue between the Cylinder 5 gas and petrol injector.

Took it to a mechanic to replace the petrol injectors to rule them out as an issue, which it wasn't, then started pulling all the connectors apart from the ECU to the injectors. Tried to find any visible wiring issues, but I've got to say the wiring for the gas system seems to be a bit overkill, would really need a wiring diagram to see what's shared between the petrol and gas injectors. So i've put trying to find the part of the wiring loom that is the problem in the too hard basket.

Haven't been able to pin down exactly where the wiring issue is, but by disconnecting the gas injector before it heats up, the car no longer stalls or misfires. Connecting the gas injector while its running on petrol causes a consistent misfire (when hot).

I had tried disconnecting all the gas injectors previously when diagnosing the issue but I suspect maybe the engine was flooded when I tried it, so I couldn't get it to start at the time which hid the problem. And poking around with the wires on the injector joins may have stopped it from completely stalling, although haven't done any thorough testing of that.

Means I have a non functioning, or 5 cylinder running gas system, but regular petrol is now working.

May look at getting a quote to replace the gas/petrol wiring loom at the place that installed the gas system, as this is the 2nd time the wiring has had issues now, and trying to hunt down the wiring issue with my current tools just isn't worth the effort. Just unfortunate that the installer is in regional Victoria and i'm in Melbourne.

 

[Fu Manchu]

I recently came across new engine harnesses on eBay. I think it was Eagle Auto Spares. They have a website.
Realistic price too. Something you could do yourself.