Rough Idle through WOT with heat light

[Oki96Cobra]

Hi from Okinawa!
Well I am probably the only 1996 Cobra on this Island and I am looking for a little help from you guys back home. I picked up this car with 57,000 miles and have done the simple tune-up items such as plugs (AL 764) Oil/PCV/Idler/Tensioner/MSD Coil packs/K&N Filter/fuel filter. When I got the car it had Ford Racing plug wires. Initially it ran pretty well with the exception of a very small stumble under 3/4-WOT and that was more likely to happen in 3rd and 4th. 5th you could notice it fairly well under any conditions. I chocked this up to probably bad plugs and was hoping to fix it after the tune up....then all hell broke loose. About 4 days ago I dropped a cylinder completely (I am pretty sure it is 8) and the car is running absolutely horrible. Under acceleration the heat light will kick on and wont go out unless you coast or come back to idle/stop. Water temp does fluctuate but the needle never comes near a danger level. It will not give me a check engine light. The only thing I thought that may have assisted this problem was that I put a can of Octane Booster and regular unleaded for normal driving to and from work. I siphoned that all out and put premium back in it. Lastly, when I start the car it runs fine at idle for about 5 seconds and then drops to about 700RPM and stumbles pretty bad. If you blip the throttle it will return to idle, run right for 1-2 seconds, and then drops back to 700 and continues to run like ^$*&. I ordered all 4 o2 sensors yesterday, but I am not a huge fan of just shotgunning parts at it and neither is my wallet! Any info would be great! Thanks!!!

 

[cbrown9064]

You need to start with the basic diagnostics. What lead you to order o2 sensors? Do a compression test. Look for vacuum leaks. Ford Racing wires are fine. Ford coil packs are also fine. I would put the stock ones back on and see if things improve.

 

[cobra_neill]

You have the Japanese export model with the pre cat heaters. That is what the heat light is for. It isn't the engine temperature. The light comes on when the car is first started to heat the catalytic converter to meet Japanese emissions standards.

It is exhaust related. Maybe you have a collapsed cat which is causing the exhaust to back up? Hard to say.

 

[Oki96Cobra]

Spent most the weekend in the shop and have narrowed it down to a bad injector on #1. Compression in the cylinder was 150psi. It was fairly obvious looking at the spark plug that there was no burn happening in that cylinder. Thanks for the heads up on the cat light. Should have waited on the O2 sensors, but at least I have some spares over here.

 

[ZeroDCX]

Good job diagnosing the issue. I'm surprised it didn't throw a P03xx code.

Before you spend more money and unless you have a spare set or noid light; Swap the injector with an adjacent cylinder and see if the condition follows to that cylinder. Also inspect for frayed or damaged wires.

 

[Oki96Cobra]

Took a good hard look yesterday at the rails/connectors and havent seen anything that stands out. I have got a whole set coming, but I might swap it just to see if it does exactly what you mentioned. The big negative of owning this thing over here is that my parts and trouble shooting options are fairly limited. I hate having to just order stuff for the sake of it, but thats the nature of the beast. I will keep you guys updated. I forgot to mention earlier, but I did swap the OEM coil packs back on and the issue remained the same. I am pretty confident spark is not the issue. Attached a photo (I know the tail lights are 94-95 I didnt do that LOL) Thanks again guys!

 

[cobra_neill]

94-95 tails are on the majority of the export models too. They made more of the 94-95 export lights than needed so they carried over to 96 and 97 model year cars. Only late 97 and 98 models had the vertical tails.

Glad you found the issue. Rockauto ships worldwide. I have a similar issue in the UK with parts etc but at least parts are cheap for these cars.

 

[Oki96Cobra]

Just put a set of Accel injectors in (24lbs) and the same problem still exists! It is 100% on #1. Voltage was checked at the connector @ 13.65-13.74 (#5 was reading identical and is not having any issues.) I also swapped a new set of NGK's last night and it obvious that nothing is firing in the cylinder. I have spark from the pack to the plug. We went as far as to jump around the connector and put leads into the injector and tap into the wires. I have also swapped #1/#2 injectors and the problem does not follow. The only code I can get is P0171 (lean bank 1) I am finding it really wierd that I can completely disconnect plug wires w/ the car running and not a single code/engine light will illuminate. It took really messing with the injector harness to get the engine light to kick on just once for us to download. Any help would be awesome. Is this a possible ECU issue? Thanks!

 

[mwolson]

DTCs get set without the CEL being set, so you need to read DTCs when you are having issues regardless of CEL state.

The vast majority of electrical problems in the world are due to connector failures. If I were in your shoes, I'd check first with a Noid light or an O-scope to verify the electrical problem. Without a Noid light (or if the Noid light shows the signal is not getting to the injector), I'd check continuity of that injector signal wire between the injector and the PCM. Inspect the connector pins for corrosion and clean them with an electrical contact cleaner regardless.

PCMs rarely fail, and I have studied the injector driver transistors somewhat. They have plenty of current carrying capacity. The only thing I can think that could hurt them is if you put battery voltage on the injector signal pin. The only way I could see that happening is if your old injector had a hard short across its pins, which is very unlikely.

 

[Oki96Cobra]

I am getting a noid light test set sent over here from the states along with 3 new connectors. Thanks for the info, I am going to do the continuity check today and see what I can figure out that route.

 

[ZeroDCX]

Check for frayed/exposed wires. Another member had a similar issue some time ago and that turned out to be his problem. Injector wires were frayed and shorting.

 

[mwolson]

If the injector signal wire frays and grounds, the injector will constantly be open as long as the frayed wire is grounded and the key is on. You can check for that condition simply by unplugging the injector connector and measuring the resistance from the signal wire to ground. If you get a very low resistance, then you can start looking for the short.

 

[ZeroDCX]

If the injector signal wire frays and grounds, the injector will constantly be open as long as the frayed wire is grounded and the key is on. You can check for that condition simply by unplugging the injector connector and measuring the resistance from the signal wire to ground. If you get a very low resistance, then you can start looking for the short.

Good to know! :beer:

 

[Oki96Cobra]

Well got it figured out finally. Long story short a new set of MSD wires fixed the issue instantly. I had previously swapped the #1 wire with #3 and was sure that the miss didn't follow the wire. I also pulled the plug initially and watched it function (spark) attached to this wire. Just a heads up to anybody down the road with the same issue double check those plug wires and if you have a spare set swap them out before diving to deep into parts/labor/time invested. Thanks again to everyone for the comments/info!