1999 Mustang GT w/ 4.6 motor. I rinsed the dust off the motor on Saturday with a gardren hose, not a pressure washer. The motor now runs with a misfire, even after drying out for a few days. I suspect I messed up a coil pack. How do I test my theory? Is it safe to unplug each coil pack one by one as the motor is running in order to test which coil may be failing? My thought is that when I unplug the failing coil, the motor shouldn't sound too different. Can I get some input here? Many thanks!
How to test for a bad coil pack - 4.6 liter motor
- Thread starter DesertStang
- Start date
I have an OBD reader, but my check engine light isn't on. Should I still plug in the OBD reader?
Unfortunately, OBD reader found no codes, even as the motor was idling with a miss and backfiring in the exhaust.
Tonight when it's dark.
Run and idle the car with the hood open. Look for lightning/arcing.
Disconnect, clean, and reconnect the MAF with electronics contact cleaner.
Do the shake and rattle of the harness in and around the intake while it's running to see if anything changes.
After that, you might start hunting down and cleaning sensor and ECU grounds.
Run and idle the car with the hood open. Look for lightning/arcing.
Disconnect, clean, and reconnect the MAF with electronics contact cleaner.
Do the shake and rattle of the harness in and around the intake while it's running to see if anything changes.
After that, you might start hunting down and cleaning sensor and ECU grounds.
OK. So, I took the intake tube (K&N) apart and cleaned the mass airflow sensor. I also cleaned the throttle body. I used contact cleaner on the connector for the mass airflow sensor. I started it a few minutes ago and it's still not idling smoothly. Next, I will remove each coil pack and will test for proper resistance on the primary and secondary coils. Do you think that's a valid next step?
Unplug the injectors one by one instead. Less chance of shocking yourself messing with an active coil. I've been zapped a few times and it hurts like a mofo.
You can unplug them with engine off instead too. TBH first thing i'd do is pull them and verify you don't have water sitting down in the spark plug holes
The mustang OBD2 might be too primitive, but later Fords have a misfire counter PID. Needs to be so many misfires before a code is generated and sometimes there just isn't. If you have that PID (and i'm not sure as i haven't plugged into mine in awhile) you can see if misfires are being detected that wouldn't trip a CEL. This might be a features that only the later OBD2 cars can do.
You can unplug them with engine off instead too. TBH first thing i'd do is pull them and verify you don't have water sitting down in the spark plug holes
The mustang OBD2 might be too primitive, but later Fords have a misfire counter PID. Needs to be so many misfires before a code is generated and sometimes there just isn't. If you have that PID (and i'm not sure as i haven't plugged into mine in awhile) you can see if misfires are being detected that wouldn't trip a CEL. This might be a features that only the later OBD2 cars can do.
WOW! I'm really enjoying the input I'm receiving here on StangNet. Thank you for jumping in. I pulled and tested all the coil packs, and they met spec. And since it's still pretty warm here in AZ, I didn't detect any water in the spark plug holes.
I haven't yet started testing the injectors, but I will do that as soon as Jeff Bezos drops off the mechanic's stethoscope that I ordered last night. You seem to understand fuel injectors pretty well, so I would like to ask a few more questions.
1. For testing, is it safe to unplug fuel injectors with the engine running? I mean, can doing that damage anything in the engine? I'm less concerned about getting shocked or burned.
2. If I find that I have a bad injector, should I replace just the bad injector, or should I replace all the injectors on that bank? Or...should I replace all eight injectors?
3. Injector prices are all over the board. My 4.6L is naturally aspirated, so I don't want to upgrade. Running stock spec injectors will be fine, I believe. Do you have a preference or recommendation for what injectors I should purchase?
I was a teen hotrodder nearly 50 years ago, so I am getting re-acquainted with doing my own repairs, maintenance, etc. My little 35th Anniversary Pony sports headers, X-pipe, FlowMaster Delta Flow 50 mufflers, K&N intake, Diablo chip, 4.10 gears, Ford Motorsports clutch upgrade. Most of those upgrades were performed by a tuning shop, but now it's time for me to jump back into my old hobby and do my own wrenching. I ordered this car in February 1999 and I waited 16 weeks for it to be built and delivered.
Thanks again. I look forward to your reply and comments.
Yes, you can pull fuel injectors while the engine is running. I do it all the time. Should be a noticeable drop in RPM and change in tone. Just unplug, note if it changes or not, and plug it back in. Won’t hurt anything.
Check the resistance of the injector coils as well. With car off, unplug and touch the two leads of a multimeter set to resistance across the two prongs. Should be about 14.4 ohms.
I actually once drove a few hundred miles on 7 cylinders with a dead injector. Was hard to detect. Had a light vibration at 3k RPM but other than that the car drove decent and had power. Obviously it ran better once I sourced a new injector.
Check the resistance of the injector coils as well. With car off, unplug and touch the two leads of a multimeter set to resistance across the two prongs. Should be about 14.4 ohms.
I actually once drove a few hundred miles on 7 cylinders with a dead injector. Was hard to detect. Had a light vibration at 3k RPM but other than that the car drove decent and had power. Obviously it ran better once I sourced a new injector.
Would you care to comment on what injectors I should select if/when I find a failed one in my motor? Should I replace more than the failed one?
Thank you so much for sharing with me.
Replace it with the same type. I would just change one. Anytime I’ve had a failed injector on one car that was the only one to ever have an issue.
Unless you have 400k miles and they are crusty, I wouldn’t overthink it
Unless you have 400k miles and they are crusty, I wouldn’t overthink it
My stethoscope arrived and I was able to hear all 8 injectors clicking away. Then I went ahead and tested all the injectors by unplugging them one-by-one. Each time I disconnected an injector, the engine ran rougher. It seems like #3 may be the problem child, as removing that connector didn't produce as much additional roughness as the other ones did. Now, the car won't idle after plugging everything back in. Did I mess something up by running the car with the intake tube removed from the throttle body? Removing the intake tube was the only way to reach the #3 injector. I plugged and unplugged #3 a couple times with the intake tube removed and noticed only minor change in roughness, so I was thinking that #3 is failing. I then plugged the #3 injector connector back in, re-attached the intake tube while the engine was running, and that caused it to stall out immediately. Now, the engine won't stay running unless I hold the tach at 2k. Did I break something, or did I diagnose #3 as failing?
I never did get the #4 injector unplugged because I could not remove the connector. I just ordered a right-angle pick so that I can release the connector. For some reason, that connector does not have the same press release that the other 7 connectors do. A video that I watched pointed out that little anomaly, too.
Thank you, Mustang 5L5.
Did you unplug the MAF/IAT at all when removing the intake tube? DOuble and triple check all the wiring and vac lines are in place and nothing was dislodged. Removing the air intake tube with the engine running would cause issues with the engine running because now the MAF isn't seeing airflow through it. It likely ran poorly because of this.
Do you have a code reader? Do you have any pending codes stored? Might be worth taking a look to se if any are stored and erasing the codes.
Do you have a code reader? Do you have any pending codes stored? Might be worth taking a look to se if any are stored and erasing the codes.
gkomo
now i can hopefully expect to receive the shaft
Would disconnecting the battery for a while and then plugging everything back in help in this situation since he ran the car without the MAF connected?
Not a bad idea. I would probably do this as well.
My gut tells me something had to come unplugged or a vac line disconnected, but i'd rule nothing out.
My gut tells me something had to come unplugged or a vac line disconnected, but i'd rule nothing out.
The misfire has been resolved. I had two rusty coil packs and spark plugs, due to rinsing off motor many months ago and failing to drive it until the spark plug holes were dry. So, we installed a fresh set of plugs and we also replaced coil packs #3 and #7. The misfire is gone, as is the smell of unburned fuel. And MPG has increased from 14mpg to nearly 20mpg. Power is now back where I expect it.
Thank you to the contributors who offered suggestions and support. Mustang folks are the best!
Thank you to the contributors who offered suggestions and support. Mustang folks are the best!
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