Those inline visual spark testers are $2 at Harbor freight. Work great. I have a 60K coil & would not try testing spark any other way. Grounding a standard coil hurts. A 60k coil will make your eyes water profusely.

 

my truck is doing the same thing. So if you find an answer please post it.

 

I recently had the same problem, truck was literally undrivable. Did a whole bunch of diagnostics myself with my limited experience and diagnostic resources. I had recently replaced the plugs so I did not at all suspect any of those and yes I did use Motorcraft basic copper core plugs. After several weeks of unsuccesful shade tree diagnostics and changing the wires and the coil I bit the bullet and took it to the local repair shop totally expecting to get fully reamed. To my supprise they told me I just had a bad plug, they put a new one and and 54 dollars later my truck was as good to go. I know you mentioned you just replaced your plugs and it did not eliminate your problem, the point I'm trying to make is don't overlook the simple and obvious solutions, sometimes they are so simple they smack you straight in the face. I got lucky and it only cost me 54 bucks.

Good luck on your troubleshoot.

 

Wow, that sounds just like this truck. I put those Motorcraft Copper plugs in there. I'm really hoping thats all it is. I finally gave up and took it to a local repair shop. I'm waiting for the phone call to find out what is wrong. I'll post something as soon as they call me!

Thanks guys for all the help!

 

UPDATE - So far the repair shop has had a tech on it for 5 hrs and still hasn't been able to figure it out. The only conclusions he'e come up with are that one side of the engine is running a bit hotter than the other. He's actively trying to figure out what could be causing that. He also thinks the problem could be the O2 sensor so he's going to test it and see if it's causing a lean condition. The service manager agreed to only charge me $200 no matter how long it takes for him to diagnose it. I feel like it's worth the money. Also the $200 will go toward the labor for the repair.

 

Update # 2 - After 8 Hrs of having a tech look at it, they are almost 100% sure the distributer is worn out and the part the spins the rotor inside is wobbling. They ordered a new distributer and are going to try it tomorrow. For anyone having the same issue, I'll post something as soon as I get another update!

 

I will def will check my plugs and distributer. Please give us an update when you find out.

 

Final Update - Bam it's fixed!!! Distributer was worn out causing the rotor inside to wobble. Shop put in a Motorcraft Distributer and module. Total bill was $650 but feels like it's worth the 2 full days it took them to fix it.

Anyone else with this problem, check your distributer for wear!

 

Thanks for the update, always helps others with similar problems narrow down suspect items.

 

Hi,
I have a similar problem on a '91 4.9L (see thread https://www.ford-trucks.com/forums/9...9-missing.html). How can you check to see if the distributor is worn out?

--
Thanks ...
Ray

 

Do you know why prostitutes eventually become Madame's? Her specs are out of acceptable tolerance's for proper function. Except w/ distributors you just replace them when the get that way.

Chewed up cap contacts would be an indication. Or distance the rotor can be moved by hand.

 

Hey Guys, I'm Back!

I got about 2 months out of the truck running great and now it's acting up again! Now it's jerking or missing only under load. Turning the A/C on makes it much worse.

If any of you guys have followed this post, you'll remember that I basically started shoot gunning parts at it with no luck. I ended up bringing it to a local repair shop and they found the distributor to be worn out. They replaced it and everything has been good up until about a week ago.

I went back to my old ways and started shoot gunning parts at it again! I replaced all the injectors. It did get better but didn't fix it completely. I've been driving around for a week with a fuel pressure gauge hooked up, and it's right within spec (30psi idle and up to 40psi under load) When it jerks, the gauge shows no change. I'm pretty much stumped again. It assume it has to be something spark related or fuel injector pulse related like the Map sensor. Stupid Ford map sensor is almost impossible to test so I would just have to replace it.

Does anyone have any other idea's? I'm really trying to stop myself from replacing the ignition module, Map sensor and TPS.

Please Please let me know!

 

I"d take it back to the same shop,they seem to have a good technician there,might cost you a little bit,but you'll be back in business. The money you're spending throwing parts at it could pay for the diagnosis.

 

I will not ague that the best thing to do is bring it back to the shop that did the work last. My only issues with that are 1 they charge $120 an hour labor because it's a large shuttle bus and 2 that it's our only work vehicle (been converted to a mobile pet grooming van) so we would be losing $200+ a day in revenue. Thank god it's still drivable, so I've been trying to work on it daily after my wife is done with her day and on the weekends. I'd really like to fix it myself if I can. The last time the shop had it, it was there for 4 days!

If anyone has any insight as to what I could have missed, please let me know. I'm very much open to suggestions! Just as a reference, below is a list of everything that has been checked or changed recently.

Please Please someone chime in!


Changed:

Fuel Filter
Plugs
Wires
Cap and rotor
Distributor
Coil
O2 Sensor
PCV Valve
All Injectors

Fuel pump in the tank is 4 months old and cat is about a year. Don't think either of those is the problem.

I pulled off the Idle Air Control valve and cleaned it. Also pulled vacuum on the EGR valve to insure the diaphragm wasn't bad and the valve wasn't stuck.

Also used a vacuum gauge to verify there isn't any vacuum leaks.

Checked base timing with spout disconnected (10 deg advanced which is correct for that year) and with spout connected to ensure the computer was controlling it properly.

Also, NO codes in the computer beside code 11 which means system pass.

 

Sounds like an ignition problem.

You said new wires, what kind? Safe to assume you didn't go "cheap"?

Plug wire heat shields, all still in place?