Hey fellow sn95 owners, I am an older guy that has always done my own repairs. I however am well versed in old school mechanics but not souch on the computer reliant beasts. I still am intrigued and obsessed with doing my own repairs but find myself very lacking when I read post that involve diagnostics of the computers on these cars. I currently have an issue with a nagging misfire. Not so noticable at idle or lower rpms but very noticeable when in hard acceleration. Seeing I due not have diagnostic equipment I have just been replacing common parts. New plugs, wires, fuel filter and injectors. I have not replaced coils yet. By what I've already spent to fix issue I probably could have taking it somewhere to be diagnosed but hard headed me says I'll fix it. Back ground; car was just purchased 6 months ago. Car is a 96 Cobra convertible. Issues that may help some help me would include cooling fan was not working when I purchased it. Previous owner had replaced temp sensor and the computer under the passenger fender. I got out the test light at checked what was obvious to me and googled the issue. Ended up connecting fans to an aftermarket two speed fan relay. Also tach works when it wants to and their is a drain on the battery that I haven't found. Not sure if any of these issues would have something common with the misfire but any of you knowledgeable mechanics can point me in right direction so I'm not just throwing parts at it. Thanks from an old shade tree
Getting frustrated
- Thread starter bobcat
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cobrajeff96
Well-Known Member
First step is to remove prior owners' janky wiring installs. 9 out of 10 times, it's a rat's nest, they don't fuse the hot wires or they tap into the OEM fuse block and overload the circuit (or they just increase the size of the OEM fuse while still using OEM gauge thickness wires which is even more dangerous), and they don't pay attention to cleanliness of grounded connections.
I'll tell ya, start simple and easy and cheap. Hunt down all the grounds and make sure they're still connected tightly, not corroded, etc. So many electrical problems can be avoided by checking grounds. It's the unseen menace.
I'll tell ya, start simple and easy and cheap. Hunt down all the grounds and make sure they're still connected tightly, not corroded, etc. So many electrical problems can be avoided by checking grounds. It's the unseen menace.
Thanks for your reply. I hate chopped up wiring harnesses on anything. For that reason I for the most part stay away for any vehicle that has been hacked up. This car has never had any splicing done to it. Even when I installed the aftermarket fan controller I did so in a way that didn't require cutting into the existing wiring. I will definitely recheck the grounds though. Thank you again for your help
cobrajeff96
Well-Known Member
Sure thing, keep us posted.
ttocs
Post Whore
lets start with hopefully the easy part, the battery drain. Does this car have the mach/premium sound system in it? The amps are known to go bad and kill batteries. Even if the entire enclosure/amp rack in the trunk was removed there is another one under the radio that people do not pull. You can yank it out or just disconnect it.
If you don't have the mach system do you have a multi-meter or know someone that does? If so we can figure it out that way it just takes a little time but it is not hard to do.
If you don't have the mach system do you have a multi-meter or know someone that does? If so we can figure it out that way it just takes a little time but it is not hard to do.
Yes it does have the Mach 460 in it. Im actually restoring the car and in doing that have put in new carpet so I did see the two amps behind the rear seat and the one under the radio while doing the carpet replacement. I exchanged the original radio/ cd player with and aftermarket double din touch screen unit. I bought a wiring harness adapter so I would not cut up the original radio harness. I utilized the Mach 460 amps and speakers and it sounds great! That doesn't mean that there isn't an issue with the amps though. I have read that the pcm may not be going to "sleep" when ignition is off. Not sure how to check that. I have read about doing a dark olms test
ttocs
Post Whore
you can test the amp theory either with the meter, or by disconnecting them the next time you are going to leave it for a few days. The rear amps are not that hard to get to disconnect depending on your size and flexibility with the small trunk opening. The front amp you can actually get to if you go to the driver side and where the console carpet meets the floor carpet pull up the console piece. Again depending on the size of your hands you can disconnect it. Now the easy way to disconnect them all would be to pull the fuse in the box which would probably be easier, no I do not know which one that will be on you.
Will try that and see. Haven't really considered the amps before now. Figured the power to them would be disrupted when key was off. Thanks. I bought a remote battery disconnect til I figure it out. It has worked well since install. I don't drive it much other than on weekends so it sits for a while
07GtS197
Well-Known Member
How old is the fuel pump? I’d suggest a fuel pressure test and compression check when you can.
ttocs
Post Whore
The amps are supposed to turn off and they did originally. I have never heard of anyone tearing into them to see why they started doing what they do but it has been a regular problem for a long time now. 20 years ago I knew how and would help people integrate and tweek the system and you really could make it sound pretty darn ok but once the batteries started dying, and the speakers were wearing out its just better to replace them now IMO.
Thanks. Sounds different from what I'm used to. I've always just attached a pressure gauge on fuel line pre carb / throttle body. Never knew there was arithmetic involved lol
Tillerman77
Member
Which wires did you use? Also, was the misfire present before you replaced the wires?
Ford Racing 9mm wires and yes the misfire was present before I bought these. One of the wires that was on car when I brought it had a damaged area on the silicone insulation. It didn't appear to be all the way into the inner core but not knowing if this damaged area could be enabling a crossfire I used some silicone adhesive to patch the spot. The mis fire remained so I replaced the wires. I did observe the damaged wire at night with engine running to see if a crossfire was present and didn't notice any
b1pig
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I've experience misfires with NUMEROUS vehicles (mostly Fords) with fuel pump issues. Its not just pressure. Its volume. The higher the engine load, the higher the flow rate. The pressure should always be constant, but you'll need a way to see the fuel pressure while driving. If the 96 has the fuel pressure PID function in the OBD2, a modern code reader with live scan or PID display will help you here.
If the fuel pressure is steady at all engine speeds and loads, you can rule out the fuel pump and filter.
If you can read the PID data, having a look at fuel trims might help. If the fuel trims are reading high positive numbers, that might indicate that the computer is telling the fuel injectors to stay open longer than they normally should... again, that could indicate a fuel flow issue, but if fuel pressure has been good it might be time to replace or service the fuel injectors.
Ignition isn't a horrible trick. Most of the same shadetree tricks work trouble shooting the modern stuff, too... but you can't lock out the timing on it.
Working on a modern car is not really much more complicated than older pre-OBD2 cars. Having the right tools in hand is the main factor.
Don't undervalue your skills and experience. It still requires air, fuel, ignition and compression to run. Use your own experience on how the engine works to troubleshoot the problem. When techno-wizardry seems to not add up, check the mechanical stuff.
If the fuel pressure is steady at all engine speeds and loads, you can rule out the fuel pump and filter.
If you can read the PID data, having a look at fuel trims might help. If the fuel trims are reading high positive numbers, that might indicate that the computer is telling the fuel injectors to stay open longer than they normally should... again, that could indicate a fuel flow issue, but if fuel pressure has been good it might be time to replace or service the fuel injectors.
Ignition isn't a horrible trick. Most of the same shadetree tricks work trouble shooting the modern stuff, too... but you can't lock out the timing on it.
Working on a modern car is not really much more complicated than older pre-OBD2 cars. Having the right tools in hand is the main factor.
Don't undervalue your skills and experience. It still requires air, fuel, ignition and compression to run. Use your own experience on how the engine works to troubleshoot the problem. When techno-wizardry seems to not add up, check the mechanical stuff.
Shove a sparkplug into the wire end boot. Make sure the terminal engages without the plug boot scrunching up. Cut off boot end a little if necessary. Coil packs are notorious for cracking on the bottom side. They also bad about spark tracking to other terminals. Be sure sparkplug well in the heads are dry.
Dont mistake missing spark with stuttering. A dirty maf sensor could be causing fueling issues
Thanks for the advice. I plan on checking out the fuel pressure this weekend. Will update as I progress
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