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Hey y’all, a few months back a i posted up a forum talking about my misfire and many said it was valves. I thought it was as well so I went ahead and changed both heads to brand new ones. Well, it fixed the problem…. A little bit she’s definitely still misfiring. When it was open, I checked the rings by putting gas in each cylinder and letting it sit for 15-20 mins, didn’t leak a single bit. Valves definitely don’t leak and the rings are still good. And the new heads solved the compression problem but I’m STILL getting that misfire a little. I checked the timing chain using the distributor and the crank pulley and it seems to be in check with the Haynes manual. There are no codes present except for 111 (no codes present). She’s got all new plugs, wires, new cap and rotor, sensors, lifters, and all injectors were cleaned and checked. I did notice that the distributor had some up and down play but I’m not sure if that would cause the problem. I have a 1994 Ford-F150 351W. Please let me know if anyone has an idea!! I’m really needing the help! Thanks!!
What do the plugs like in terms of color? The SD system like to run lean so it wouldn't take much to make the motor too lean and misfire prone.
Is the air injection system present and in good condition? How old is the MAP sensor?
What do the plugs like in terms of color? The SD system like to run lean so it wouldn't take much to make the motor too lean and misfire prone.
Is the air injection system present and in good condition? How old is the MAP sensor?
The plugs looked alright. The electrode was a little brown though. I didn’t think it would look like that since they’re literally brand new. The smog pump was deleted when I bought the truck but the EGR is still there and works good. MAP sensor I changed about a year ago
Ok so pump is deleted, what about all the plumbing? There cannot be any fresh air getting into the exhaust upstream of the O2 sensor, if the plumbing remains and the diverter valve, check valve or crossover tube(all behind the motor) leak in any way that could be your problem. And a leak could be internally through the valve which won't be audible, it doesn't have to be an obvious exhaust leak to pass fesh air into the motor.
From your other thread, and the link to 'How to Test Engine Compression', your cylinders #2 and #7 are miss firing.
Also, the link with 'How to Test Engine Compression' is missing a very key step....WOT
Do another compression test, correctly:
- pull all plugs
- use a remote starter, or remove fuse for ignition
- throttle held wide open
- crank engine
- record each cylinders compression
Compare with your previous compression results. If compression >135 everywhere, you had some sort of valve/head issue.
If your compression results are the same as previous, continue testing:
- on the low cylinders, use a small amount of OIL, put into the cylinders
- check compression on that cylinder with oil in it
If the compression jumps, you've got ring problems.
these are the compression tests. As you can see they all rose. Did the wet test on 2 and 7 and they stayed the same. I was questioning 4 and 5 but according to the Haynes manual they have to be within 75% of the highest cylinder which would mean compression in all cylinders are good
You can hear it through the exhaust. I replaced the FPR over the summer because I thought that was the problem. I’ll check the vacuum tomorrow. How much vacuum should I have at idle? I will also organize the plug wires better too. They don’t have any of the little plastic things on the valve covers so I’ll have to buy more
You can hear it through the exhaust. I replaced the FPR over the summer because I thought that was the problem. I’ll check the vacuum tomorrow. How much vacuum should I have at idle? I will also organize the plug wires better too. They don’t have any of the little plastic things on the valve covers so I’ll have to buy more
If you're pulling at or about about 18 inches of Hg at idle, you're fine. Higher is better, in general, I *like* to see 22 or so.
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