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Confused about spark plug gap/timing on 87

MuricMustang

MuricMustang

New Member
(I am new to foxbodys FYI) So I bought this 87 mustang its got a cam a little machine work done and heads. I am confused about the following things.

- the timing is at 10BTDC (thought it should be like 12-14?)
- spark plugs are gapped at 0.60 (thought it should be 0.54?)
- he said to only run 91 octane in it (why would this matter if it isn't tuned?)

I have never seen this and im a little confused to why these are the way they are. Any ideas would be appreciated.

That spark plug gap seems excessive but when I tried .50-0.54 it ran like crap, same when I tried to bump the timing up slightly.
 
Blueknights75

Blueknights75

Active Member
Congratulations on your fox body purchase!
Has your Fox been swapped over to Mass Air or is it still Speed Density?
My 87 is pretty much stock minus a cold air intake and flowmasters. You are absolutely correct that the factory spark plug gap recommendation is .54 and the timing from the factory was set to 10 degrees TDC. I bumped my timing up to 12 degrees and only run premium fuel. I am sure someone with more knowledge pertaining to the engine mods you have done will chime in to help.
 
broncojunkie

broncojunkie

Well-Known Member
If your car has heads (or head work done), chances are they are smaller chamber for increased compression. The higher octane requirement is to deter detination. This is particularly true with iron heads. Aluminum dissipates heat a little better, which means (in theory) you can run a little more timing or lower octane, although, the higher octane stuff is always a good safeguard when you increase compression.

You should be able to run a little more timing than 10 btdc, but the truth is that your setup is going to like what it likes. Each scenario is different, once you start modifying things.

The plug gap situation is similar. If it likes more gap, I wouldn't sweat it. However, you might be running too hot of a plug for your setup. Whatever brand of plug you're using, you should be able to find a list of heat ranges for them. I will tell you that NGK really focuses on heat range more so than the other brands. They have a broader range and they're good about listing heat range info. If you're running a hot plug, that could explain the timing and plug gap issues.

Hope this helps!
 
MuricMustang

MuricMustang

New Member
@broncojunkie wow thanks so much! im still learning so I appreciate explaining how that stuff works. I can run more advanced timing but at 10 the lope of the cam sounds mean hahah when its advanced it makes it less noticeable and low end is fine so ill prolly leave it just was most concerned about spark plug gap since everyone else seems to run stock or lower.

The ones in the car were Bosch HR9BPY Double Platinum

I put in Motorcraft Platinum after this and has ran better.

Only issue I run into with the first start in the AM it starts then putters sometimes dies then starts again and its fine lol. idont know if its tuned or not and maybe the tune isn't kicking in right away? or maybe there is a timeframe before the computer can adjust for the CAI I have installed and other stuff im just really not sure

I was going to take it to a local place and get it tuned and pretty much say "make this thing run great" lol
 
broncojunkie

broncojunkie

Well-Known Member
You might check into a leaky injector or two. If your oil smells like gas, that's a good indicator. If you seem to be making oil (level rising), that's another indicator. I just mention this because it is one possible cause for a hard cold start that you want to rule out.

You can also pick up a cheap spark tester to see if each cylinder is getting a good spark.

Pull the vacuum line off of the regulator and make sure no gas drips out (which would indicate a bad regulator). It also doesn't hurt to check fuel pressure with a gauge. Change fuel filter and do a basic tune-up. Clean the maf, too! And make sure the coolant temp isn't too low.

All of these are common problems I've come across. Good luck! Let us know how it goes.
 
MuricMustang

MuricMustang

New Member
@broncojunkie life saver! Oil does smell like gas when I changed it last I couldn’t figure it out I will replace the injectors! Thanks man

Edit* Well im googling it and it says it usually has problems with warm start if its leaky injector mine is sometimes the first cold start and that's it after that
 
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broncojunkie

broncojunkie

Well-Known Member
The way you describe it (starts, runs poorly and sometimes dies, then starts and clears up) makes me think your fuel rail is empty. There is probably still some fuel behind the good injectors, but the leaking ones cause the rail to drain. It will start up, but immediately runs out of fuel until the pump can replace it. The fact that it happens after sitting a while makes me think this is what's going on. It would take some time for the rail to empty itself through a couple leaky injectors.

If you had access to a scope, you could probably peek in through the plug openings and tell which one(s) were the culprit.
 
MuricMustang

MuricMustang

New Member
Hey thank you! Such detailed response and helps me learn how these cars work haha

I’ll definitely replace them just for the fuck of it and if it doesn’t fix it I may test fuel pressure
 
MuricMustang

MuricMustang

New Member
haha I bet. Other thing I was curious about my car is 87 and MAF conversion. its possible he put in too big of a MAF and didn't program it to injectors right? would that cause similar issues?

Or when he did MAF conversion I wonder if it still has 87 computer and he didn't swap for 89+ I should look how to tell the difference because if that's the case I bet the 87 computer is dumping gas

going to check and see what computer is showing and see where to go from there

After checking mine has an A97 which is mustang California mass air ( I don't know the difference lol)

More research A9l and A9S seem to have minimal differences and shouldn't cause issue since my MAF and computer match.

That leads me to believe it is leaky injector or MAF isn't tuned to injectors
 
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347HO

347HO

Active Member
You don't necessarily replace the ecu, because there's a "piggyback" converter which plugs into the ecu connector and allows the ecu to accept the maf inputs.
Check for such a device on your ecu.
 
MuricMustang

MuricMustang

New Member
347HO said:
You don't necessarily replace the ecu, because there's a "piggyback" converter which plugs into the ecu connector and allows the ecu to accept the maf inputs.
Check for such a device on your ecu.
Click to expand...
@347HO yes idid disconnect spout before timing and then replaced after. I took a pic and I have a A9S which is from California 88 cars if im not mistaken so I think he did replace it. here is pic of my computer https://ibb.co/h1ZXDDr thanks for your help
 
broncojunkie

broncojunkie

Well-Known Member
Aftermarket maf can be calibrated for different size injectors, so just make sure your injectors match the maf and you should be good. I also can't stress cleaning the maf too much. Those things are really sensitive and you can't tell it's dirty by looking at it.

Orange injectors should be 19#, which is stock size. 24# is a common upgrade and are typically grey.
 
MuricMustang

MuricMustang

New Member
So
1. It isn’t aftermarket MAF it’s Off an 88 and so is the computer I guess. (This MAF has no needle never seen it like that how do you clean it?)

2. Here’s a video of how it starts up https://streamable.com/kcwnu5

3. I assume since it’s off a 88 5.0 I would just need to make sure I have orange injectors right?

confirmed they are orange

Thanks
 
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broncojunkie

broncojunkie

Well-Known Member
After watching your video, it doesn't seem like it's starving for fuel. So that's good. And yes, you are correct about the injectors. Stock maf should have orange (the only exception I know of is the 93 cobra. It had 24 lb injectors. The maf was the same, but the ecm itself was calibrated for 24 lb.)

Have you pulled a couple plugs and checked them? There are several things that could cause your start-up idle issue. The IAC could be dirty (along with the egr spacer where the iac connects or the throttle body itself). The throttle position sensor could cause it. You might just need a fresh fuel filter or have some gunk in the pick-up strainer.

Does it run well after it warms up?
 
Blueknights75

Blueknights75

Active Member
Just be careful with injector coloring…I just replaced all of mine with stock 19lb injectors from LMR, and the stock 19lb injectors that were the factory injectors were orange. The replacements I got from LMR (still 19lb) are grey.
 
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