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Discussion Starter #1
I posted here awhile back about a 1999 Mustang that I bought at auction with a few problems. I have most of them sorted out, but I have an intermitten miss that I have yet to solve. It missed on the drive home, and still misses. The spark plugs in it were pretty worn out and were Bosch, so the first thing I did was put in new NGK plugs and Denso plug wires. The old plugs while worn, all had a nice mocha/carmel color, no oil/bridging/ect.

Still missing. I put in a new coil. Still missing. I have triple checked the plug wires for fully seated. I have ohms tested the coil (both old and new one). I checked the MAF as per this and it checked fine. I have checked fuel pressure as per Alldata specs. I have done the old injector trick were ya stick a screwdriver to them and listen at the handle like a stethoscope, they all click and none sound any different than the others. What are other ways to test injectors?

I have no check engine light (bulb works). It does not miss 100%. It mostly misses while climbing a hill in high gear. If I push on it hard enough to make it downshift it will quit most of the time. Does not miss at idle, ever. Starts fine. Live on a very secluded 2 lane blacktop, as such I don't like to drive it fast (done hit one deer and only lived here 6 months), but there is a bridge about 1/2 mile long I use when I need to put my foot in it. It misses there when I do that sometimes, but not every time.

Ideas? I'm about out of them.
 

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Sounds like crap gas...

Is it missing at idle as well?


Edit: It could also be the one or both of the front O2's going bad.
 

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Discussion Starter #3
No miss at idle.

I'm considering bad gas as well. It had half a tank when I bought it, I filled it up at my normal place but that's still half a tank of (potentially) bad gas in there. Today I dumped 2 cans of HEET in it, have yet to drive it though.
 

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Discussion Starter #4
Just drove it 40 miles after putting in HEET. Still missing the same as before. Getting frustrated.
 

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Have not checked compression. Do not have compression tester. Oil looked fine, as did spark plugs, and no smoke... so assumed compression is good. If it comes down to it, will buy compression tester, but for now trying all the free/cheap stuff. (except the plugs and wires, it needed them)
 

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Have not checked compression. Do not have compression tester. Oil looked fine, as did spark plugs, and no smoke... so assumed compression is good. If it comes down to it, will buy compression tester, but for now trying all the free/cheap stuff. (except the plugs and wires, it needed them)
inspect power wires at coil and Fuel pump, anywhere vital, maybe use some dielectric grease. clean or check battery post terminals. try to somehow listen to fuel tank for a fault uphill or under load whtever, have an assistant near trunk or use a microphone. if you cant find anything maybe try new crank sensor, coil, or fuel pump. GL
 

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Discussion Starter #8
I have checked what wires I can get to, also used dielectric grease. I cleaned terminals when I disconnected the battery to reset ECM (don't hurt to try).

However, listening is an idea I hadn't thought of. The more I drive it, the more I think it's the hill, and not the "under load" part, because one time today I got it to miss while I was stopped on a hill. I actually went back to that place and stopped there again, in an effort to make it miss long enough to throw the CEL but it wouldn't do it the 2nd time. I will try again parking on various hills and if it happens I'll try to listen. I'll also leave it there for a few minutes to try and make it throw the CEL.

Anyone know - is it the severity of the miss that will turn on the CEL, or is it the repeatability/reoccurrence? Cuz the miss is pretty severe sometimes, it just doesn't do it very often/very long.
 

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Could possibly be cats getting clogged up as well. Does it miss like crazy for a bit, then come on strong?
 

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Discussion Starter #10
No not really. But I had a 1997 Dodge Ram pickup that was running great one day then just stopped on me on the way to town. Fooled with it and found it would run but die if I have it gas... idled my way to a parking lot. Towed it home the next day, unbolted pipe from the header/manifold and that cured it. Drove it that way to a shop and had the cat removed and the pipes bolted back tight.

Could I do the same thing on this to test? I know if I do it on my Toyota it will throw the check engine light because of a 02 sensor below the cat.

I haven't spent much time under the car yet.
 

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It won't hurt anything to do that, there are a total of 4 bolts/nuts to seperate the mid pipe from the manifolds on these cars. If it does give a code, just reset it and all will be fine.
 

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Simple/cheap things to check/replace, any one of which could cause a miss under load:

Replace the air filter
Clean the MAF
Replace the fuel filter
Verify that you do not have any vacuum leaks
Verify that you do not have any leaks in the EGR system
Verify that the EGR valve opens when vacuum is applied
 

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Discussion Starter #13
Today I drove it another 40 miles on 2 lane blacktops that have like NO people so that I could try various things such as stopping on hills and what not. Didn't learn much other than that I found a hill that causes it to miss on and off for a good 30-45 seconds til I reach the top, would not miss if stopped on the hill though.

Did not check injectors. Thought there was more room. Guess I gotta unbolt that upper intake to check them.

Also did not unbolt the cat because I ran if first. I did pull all 6 spark plugs, thinking perhaps I bumped one and bent the electrode in. Nope. I had an idea though, the wife is the manager at a grocery store/gas station and was telling me they have a paste that they stick on the stick for sticking the tanks (say that 3 times fast) that turns red when it encounters water. She is going to bring some home and i'mma put some on a hose and stick it down into the tank.

Also, for the heck of it, pics of oil, trans fluid, and spark plugs. Note that plugs only been in for 100-150 miles.






Drivers side plugs.


Passenger side
 

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a.k.a. Racecougar
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I had an idea though, the wife is the manager at a grocery store/gas station and was telling me they have a paste that they stick on the stick for sticking the tanks (say that 3 times fast) that turns red when it encounters water. She is going to bring some home and i'mma put some on a hose and stick it down into the tank.
That won't be easy to do with the anti-siphon valve in the filler neck.

One other simple thing to doublecheck is that the plug wires are on the correct terminals at the coil pack. People have a tendency to mix up the #5 and #6 wires, which will often only show up as a miss under load at lower rpms.
 

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Discussion Starter #15
I got it past the anti-siphon... never realized there was such a thing (hey, I don't siphon gas lol) but I used a piece of wire and it went past. No water.

I have checked the plug wires for crossed multiple times, but I checked them again as per your suggestion.

I also checked the TPS as per this and it checked out.

Also checked EGR valve. It checked out.

By my count, I've checked or replaced -

Coil
Plugs
Wires
EGR
TPS
Checked MAF for operation
Fuel Pressure
Sprayed carb cleaner to check for vac leaks
Hooked up vac gauge, read 21 at idle
Air Filter

I think I have these things left to check -
Clean MAF
Catalytic convertor
Fuel injectors
02 Sensors
The things that go with EGR (DPFE Sensor, EGR Valve Vacuum Regulator Solenoid)
Compression (though, in my experience, there'd be signs)

If that all checks out... replace fuel filter, if still bad, replace fuel pump, if still bad, burn to ground! Haha.

Is there anything I'm forgetting or missing?
 

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a.k.a. Racecougar
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I have checked what wires I can get to, also used dielectric grease.
Hopefully you only used dielectric grease on the boots and not any terminals. Dielectric grease is an insulator, not a conductor.

I'd clean the MAF, then replace the fuel filter, then consider unbolting the cats.
 

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My father in law had an 01 in the shop the other day with the same ailments as you describe, and that particular one ended up being the DPFE. Just thought I'd share, but obviously there are a number of different things that could cause those issues.
 

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It wouldn't hurt to remove both hoses from the DPFE (one at a time so that you put them back on the correct way) and shooting some compressed air down them into the EGR tube. The hoses can get clogged up and cause faulty readings at the DPFE.
 

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before i would replace the pump i would try some 2-cycle oil in the gas on a low tank to see if it eleviates the issue but im sure some of you will think this is a bad idea. i would try to get the gas around 70-80:1 to lube the pump and injectors. if you do use a high quality 2 stroke oil.
 

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Discussion Starter #20
Today I did not have time to work on it, but I bought a fuel filter and MAF cleaner and will get to those things as well as the DPFE, unbolting cats... Deer season here tomorrow for 3 days so prolly won't get much done then.
 
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