Ford Mustang Forum banner

Status
Not open for further replies.
1 - 7 of 7 Posts

·
Registered
Joined
·
20 Posts
Discussion Starter #1
OK, to start, I had to rebuild the engine in this 1997 Mustang GT. I put all forged internals with a main cap girdle. I was going to use a pair of PI head from a PI swap kit, but the factory they were assembled in bent one of the valves. I had to get the car running so I reused the 120K non-PI heads. The car fired up with no problems, but at idle and under heavier loads it shakes the crap out of the car. I looked at the plugs and all but one shows normal combustion of light brown. #3 plug is perfectly clean and white except for alittle carbon on the end of the threads. I checked the wires, they were locked. I tested the injectors, 15 ohms and the motor stumbles when I unplug them. So what else could it be? The old heads looked fine with no valve leaks. Anyone have any ideas? BTW, I am alittle new at Mod Motors.
 

·
Registered
Joined
·
5,633 Posts
Sounds like an issue on #3 all right. Might be a bad plug (happens sometimes), wire, or issue with the coil.

As for what else it could be...

Not hard to get off with the cam timing. Did you degree the cams?
 

·
Registered
Joined
·
20 Posts
Discussion Starter #3
Sounds like an issue on #3 all right. Might be a bad plug (happens sometimes), wire, or issue with the coil.

As for what else it could be...

Not hard to get off with the cam timing. Did you degree the cams?
This car does have the 4-post coil pack instead of the newer coil-on-plug setup. I did unhook the wire from the pack to that cylinder. The engine did change tone and it drew a long arc while reconnecting it while running. I thought this kind of ignition system was a waste fire setup. If the pack was bad, would I have two cylinders not firing right? I have the spark plug gap set to .052" per the manual, is that too wide?

I haven't done a compression check mainly because I haven't had time to work on it. I have thought if the injector for that cylinder was plugged up from old fuel or debris. It was parked for little over a year by the previous owner and he started it only every couple of months. I also have the intake manifold off the car for almost two months. Could the MAF sensor be dirty and causing a bad signal?

As for cam timing, I used the original cams and heads just to get the engine running and broke in. Those part has over 120K miles on them, maybe they are just wore out.

I lined up the timing marks as per the manual and that's it. If it is off a tooth, I wouldn't expect it to run at all. But like I said in my previous post, it smooths out on lighter loads. It could have been a pre-existing issue that the previous owner wasn't aware of because of the factory rubber engine and tranny mounts. I have polyurethane motor and tranny mounts now.
 
P

·
Guest
Joined
·
0 Posts
a clean plug could be the sign of coolant burning and steam cleaning the plug. pressure check your coolant system and check the cylinder head gaskets.
 

·
Registered
Joined
·
5,633 Posts
Plug

Correct, but wiring issues (and cracked insulation, arcing, etc) are common in this vintage. Getting spark to the coil is good, but does not prove that you have spark to the plug (or that the plug is doing its job). Swapping out a plug is not expensive or tough.

94baby, that's an interesting idea. NoLongerStock, are you getting white smoke out of the exhaust and/or the smell of coolant?

Gap is OK.

LOL, yep, with that description, you could have anything in there gumming up the works. If no fuel is getting to that cylinder, that plug will not show much effect, just like if there is no spark. Sitting up could have clogged an injector.

A dirty MAF would not explain the spark plug.

Oh yes, it will run off that much, and about as you describe, too. These engines once they get old can easily be off a good bit if you take them apart and then put them back together. Degreeing the cams is highly recommended, even if you are going back in with all new parts. The precision is not really that great as it comes from the factory - there's a "luck of the draw" element.

The urethane mounts will transmit a lot more vibration into the passenger compartment.



This car does have the 4-post coil pack instead of the newer coil-on-plug setup. I did unhook the wire from the pack to that cylinder. The engine did change tone and it drew a long arc while reconnecting it while running. I thought this kind of ignition system was a waste fire setup. If the pack was bad, would I have two cylinders not firing right? I have the spark plug gap set to .052" per the manual, is that too wide?

I haven't done a compression check mainly because I haven't had time to work on it. I have thought if the injector for that cylinder was plugged up from old fuel or debris. It was parked for little over a year by the previous owner and he started it only every couple of months. I also have the intake manifold off the car for almost two months. Could the MAF sensor be dirty and causing a bad signal?

As for cam timing, I used the original cams and heads just to get the engine running and broke in. Those part has over 120K miles on them, maybe they are just wore out.

I lined up the timing marks as per the manual and that's it. If it is off a tooth, I wouldn't expect it to run at all. But like I said in my previous post, it smooths out on lighter loads. It could have been a pre-existing issue that the previous owner wasn't aware of because of the factory rubber engine and tranny mounts. I have polyurethane motor and tranny mounts now.
 

·
Registered
Joined
·
20 Posts
Discussion Starter #6
Correct, but wiring issues (and cracked insulation, arcing, etc) are common in this vintage. Getting spark to the coil is good, but does not prove that you have spark to the plug (or that the plug is doing its job). Swapping out a plug is not expensive or tough.

94baby, that's an interesting idea. NoLongerStock, are you getting white smoke out of the exhaust and/or the smell of coolant?

Gap is OK.

LOL, yep, with that description, you could have anything in there gumming up the works. If no fuel is getting to that cylinder, that plug will not show much effect, just like if there is no spark. Sitting up could have clogged an injector.

A dirty MAF would not explain the spark plug.

Oh yes, it will run off that much, and about as you describe, too. These engines once they get old can easily be off a good bit if you take them apart and then put them back together. Degreeing the cams is highly recommended, even if you are going back in with all new parts. The precision is not really that great as it comes from the factory - there's a "luck of the draw" element.

The urethane mounts will transmit a lot more vibration into the passenger compartment.
Most of the motor is new except for the head/cams. I can't imagine that it can be that far off with a stock engine. I degree cams if it was a purpose built motor, but alittle over kill for a stock rebuild. I also have new plugs and wires. The more I thought about it, I went ahead and ordered a set of injectors. BTW, does anyone know if the Steeda CAI kit for that year of car comes with a larger MAF sensor or does it reuse the factory one. This was installed by the previous owner.
 

·
Registered
Joined
·
5,633 Posts
These engines can come from the factory off 3-6 degrees. This is common. But I'm not pointing at this as your culprit - I still think you have an issue involving the one cylinder/spark plug/wire.

If the new injectors don't fix the problem, revisit that spark plug.

That CAI didn't include a MAF unless the purchaser paid extra for it. I would consider this unlikely, particularly since a larger MAF is not needed for that application.
 
1 - 7 of 7 Posts
Status
Not open for further replies.
Top