weak cylinder

[famousguy_fsas]

so i have been tracking down what the shimmy is in my truck. had my dad drive it and he says its for sure a cylinder miss. it doesnt miss at idle. it doesnt miss while driveing fast. only when a little pressure is put on the truck. not to much pressure. just when its at a 2000 or a little less rpm cruising speed. now i know to check all the normal things. wires are just replaced. cap and rotor just replaced. high preformance ignition coil just put in. checking the plugs her in a few min. i know its not a bad ring cause i literally never have any smoke out of the exhaust. not even the littleest amount. im willing to bet ill find a fowled plug. what could be the cause of that? clogged injectors? was the best injector cleaner anyone can recomend. someone said if it was a bad valve i would here it and u cant. my engin sounds great and even runs great 80% of the time. just bad at that one time and idol i mentioned. its a 86 5.0 efi

 

[gatorbronco]

What type of gas do you use (87, 89, 93)? It could be that under light loads your engine is detonating and causing the shudder. Have you checked your timing also?

 

[famousguy_fsas]

ya timeing is good. checked it. i did notice today that my air box had no clips holding the top to the bottom. is it possible that dirt got in there and clogged up my injector? does anyone know of a amazing injector cleaner? anyone ever hear of a cleaner called redline?

 

[Ilduce]

i like using seafoam. seems to do the job pretty good.

 

[shift1313]

Check your plugs and the gaps on them first. I would find it hard to believe only one cylinder was missing unless it was an injector problem. I like seafoam as well. I had an issue and i know of others who have found a loose spark plug. The fact that you have a new rotor/cap id guess its not an issue actually getting spark.

One other thing it could be is a bad oring sealing your injector. If you are getting extra air in one cylinder it could lean out enough to detonate.

What is your base timing set at? how was this done?

 

[famousguy_fsas]

where can i get sea foam? at any auto parts store? and as for my timing i dont know i dont mess with it. i had my mechanic friend check for me. just got fired and been busy lookin for a job. but im checkin my plugs in the morn. what should they be gapped at? now lets just say i do find a clogged and fowled up plug. what would be the cause?

 

[Broncobill78]

If I'm reading this correctly this is an 86' EFI Bronco. 86' trucks were CFI not multiport correct ? Ford upgraded to MFI with the big nose 4th generation trucks so I'm not seeing how an injector problem would effect a single cylinder. Sure it could make it stumble at certain revs but a miss ? Before getting crazy with anything I'd go back and make sure it IS actually a skip before proceeding any further. Although I suppose rather than just guessing it'd be more appropriate to just ask if the truck is MFI or CFI /emoticons/[email protected] 2x" width="20" height="20" />

 

[Ilduce]

where can i get sea foam? at any auto parts store? and as for my timing i dont know i dont mess with it. i had my mechanic friend check for me. just got fired and been busy lookin for a job. but im checkin my plugs in the morn. what should they be gapped at? now lets just say i do find a clogged and fowled up plug. what would be the cause?

.044 should be oem gap. but seafoam u get from any part store.

 

[Broncobill78]

now lets just say i do find a clogged and fowled up plug. what would be the cause?

usually it's either blow-by from worn rings, it's running too rich or the plug is too cold

 

[famousguy_fsas]

my truck is efi fuel injection. it only is running of seven when you are trying to maintain a speed. like if im cruising at say 45 and im the gas just enough to keep it at 45 then it gets a tugging sensation or shutter from it running on 7 but every other time its good

 

[Broncobill78]

Yes, but is it a throttle body (CFI) or multiport (MPEFI) ? A CFI engine looks like a standard carb'd engine with the usual intake manifold but instead of a carb it has a throttle body (which looks a lot like a carb). 85 & 86 Broncos came stock with CFI, in 87 they switched over to MPEFI. Multiport engines have individual injectors for each cylinder (8 injectors total) and if one goes bad then sure, the engine will start running on 7 cylinders. CFI engines work just like carb'd engines and a clogged or otherwise bad injector will effect ALL cylinders not just one, just like a bad carb. If it's a CFI engine and you're sure that a cylinder has dropped out then you're looking at an ignition problem, if it's multiport then it could be *either* ignition or a bad injector. I understand the engine is fuel injected, I'm just asking if it's multiport or throttle body. It came from Ford with a throttle body back in 86 but that doesn't mean that sometime in the past 23 years someone didn't swap in a multiport setup.

 

[shift1313]

Not the greatest pic but here is my old 86 f150 that was 5.0.



Here is an 89 bronco 5.0

 

[BroncoJoe19]

Let me throw this out there... if it is stammering at a certain RPM range, it could also be a faulty TPS.

 

[famousguy_fsas]

mine looks like the first pic. it has the cold air intake with the filter on the top of the engine not the side. so what one does that mean my engine is. also i figured out the problem cause i just bought the truck like 2 weeks ago and normally i would but the plugs sooner but i didnt this time. but one of the plugs gapping was completely smashed there was no gap. the prong was touching the diod thing or whatever you call it. but now it runs great except for one thing. every once in a while the truck will just randomly die. but will start right back up and drive perfect and wont do it again for like another week or 3. but it doesnt bother me so im not worried bout it to much. thanks everyone for the help

 

[BroncoJoe19]

If it randomly dies as you are making a left hand turn in the face of oncoming traffic, that could be fatal.

I'd suggest that you make a serious effort to correct that problem!

Pull Diagnostic Trouble Codes (DTCs) From your onboard computer.

Your engine and transmission are computer controlled.

The computer uses sensors to tell it a number of different things and it controls actuators that push or pull mechanical levers (kinda). If one or more sensors aren't working properly, the computer goes "blind" and doesn't know what to do. If the computer can "see" but one of the actuators is broken and therefore can't follow the commands of the computer; the engine won't run correctly. The computer is preprogrammed with set values for each of its sensors, and each of its actuators. It will run a self check of all systems, like the space shuttle; it will compare its set value(s) to the value(s) it recieves from its sensors, and actuators. If any sensor or acutator is out of the "normal" range the computer will generate a "code." It will generate some codes on the fly, and others will be stored while you are driving. There is a simple method to "pull codes" out of the computer for one to use for diagnostic purposes.

Earlier versions of On Board Diagnostics OBD 1983-1995 can flash the error code to the dash board and can be pulled in one's driveway without any special tools.

Later versions of On Board Diagnostics OBDII some 1995, and pretty much all 1996 and newer, require one to use a code reader or scanner tool.

Some auto parts stores will scan your engine codes for FREE, you may want to call around. Some will scan OBDII but not the older (prior to 1996) OBD systems.

SO here you go...

How to scan FORD on board Diagnostic Trouble Codes (DTCs) in your driveway

Howto Pull Codes 1983-1995 Broncos, Mustang, F series Trucks, Econolines, 302, 351 and more

 

[famousguy_fsas]

i know how to pull codes but if no engine lights are on and they all work will there still be a code to be read? and it only does it every once in a while at like under 5 miles an hour

 

[BroncoJoe19]

Sometimes. It did with my MAP sensor.

 

[BroncoJoe19]

You might want to give her a good looking over for vacuum leaks

Checking for vacuum leaks.

Some of the sensors and some of the actuators either read the amount of vacuum, or use vacuum to move controls, therefore it is important to the proper functioning of the engine that your vacuum system is fully intact. Otherwise one may get codes falsely indicating that there is a problem with a controller/actuator, or a sensor when in reality it is caused by a lack of vacuum.

Look at your rubber vacuum hoses (they are about 1/4 - 3/8 inches in diameter, if they are dry rotted or cracked, replace them. IF they slip on/off of their connectors too easily, they may have stretched out a little bit, cut the ends off, and put them back on.

You may listen for a leak. Sometimes using a cut off piece of garden hose is a good aid to listen with. Sometimes a cardboard tube (like from gift wrapping paper) is helpful. Just remember that whenever you stick your head inside a running engine compartment, that you are not wearing any loose clothing or jewelry that can get caught.

Another suggestion is to use a spray can of carb cleaner and spray around the bottom of the intake manifold, and the base of the throttle body assembly. IF there is a leak, you should hear a change in your engine.

Keep a fire extinguisher handy, or use water instead of carb cleaner (it works, but not as well.) Be aware that if you use water and the wires get wet and it runs worse... your wires may be bad, and the water is allowing them to arc instead of jump the gap of the spark plug.

Another suggestion is: to take a propane torch, turn it on (but don't light it) and move it over the vacuum hoses and connections. The engine RPM's will increase if there is a leak and the propane gets sucked in.

Courtesy of TheOldWizard ford-forums... Don't forget to remind folks to check the PCV valve, hose and grommet !

Courtesy Ramnasal ford-forums... Clamp off the hose that runs to the vacuum booster (brake booster) or pull it and plug it. It is possible that the diaphram on the inside of the booster may go bad and cause a vacuum leak.