I need a place to start and this forum has always came through. I have a '90 F150 4x4 with a 5.0 EFI.

Recently I had to replace a bad plug wire. The symptoms where hesitation, backfiring and a noticable miss. After replacing this everything was great for a few weeks.

Now I am back to the same thing. I have duel exhaust with no cross over and the miss is always on the passenger side. This is very noticable at the tailpipe. Also it seems to run or get worse the more I drive it. Almost to the point of not really wanting to run. It does idle fairly well except if you rev it. When it idles back down there is a noticable lope. Sounds like I have a race cam (wish I did). Plugs are relatively new, less than 3k on them. The engine does have 170k and burn oil.

What is the easiest way to diagnose this issue? I thought about pulling one plug wire at a time. At least I could find which cyclinder is the problem. I have thought about a possible fuel pump issue or a clogged injector but the pump would not miss only on one side and the injector would not get worse the hotter it got. At least I don't think so. I am thinking it is more like a head gasket or ???

Any ideas??
Thanks

 

you said you just replaced 1 plug wire, the rest probably need replacing if 1 went bad

 

I thought about that. They all look decent, the only reason I had to replace the one is that the wire pulled out of the boot and clip. It was only make intermitent contact. I just don't want to buy a whole new set if it could be something else. It is just strange that it is on the same side as before.

 

replace ALL the ignition wires.

replace the plugs.

 

Ok, I understand the reasoning behind both. I guess what still bothers me is the fact that if you drive it for, say 20 minutes on the highway, it really loses power and starts running rougher. When coming to a stop you almost have to gas & brake at the same time to keep it running. I know that fouled out plugs will get worse the hotter they get but I have never seen this condition.

I am really wondering if with 170K and burning oil, 5qts. in 2 month, if it is just time to retire the ol' 5.0.

 

You can't go by the looks of the plug wires, they carry big voltages and can break down electrically while still appearing fine, so the only way to gauge thier condition is to test the resistance or voltage loss. If these wires are more than a year old and are anything but Motocraft wires they are suspect, they should measure between 6000-7000 ohms per foot with a multimeter, significantly higher than this and they're toast. Start with this and if the wires check out then you should test/examine the other spark components including the coil, distributor cap, and button for excessive wear. These motors also have the TFI module mounted on the distributor, and these are known to begin to fail at higher temps, but don't change this until you have eliminated everything on the high voltage side of the ignition.

 

Thanks, I'll check the wires out tonight. When it does hesitate, say on takeoff, if you take off slowly it is ok. But if you take off quickly you will usually get a good cough and small backfire. It does sound like a timing / ignition issue when cold. Luckily I only have 2 miles get to work and home. Not usually drive far, especially now.

 

Update.....I finally had the time and funds to do a little work on the 'ol girl. Turns out there was a bad plug wire. The wire and boot pulled off leaving the clip and part of the wire on the plug.

New wires, cap, rotor and plugs. Runs much better but....here we go.

On quick take off or acceleration there is still a back fire. Sometimes several before it takes off. The sound if muffled and not in the exhaust so I am assuming that it is detenation in the chamber.

Question...could it be a plugged injector? At this point I am hesitant to put too much more into it. 170k and burns oil. She is getting tired. I can get a new, ok not new but less miles, engine for $300 - $400. It comes complete with everything. I know that the little things will add up quickly and if it is a tire motor that is partially to blame, I just need to cut to the chase and replace it.

Any suggestions? I need to do a compression check but...old fat guy + hard to reach plugs = fun for everyone but me!!

 

what kind of plugs did you use?

 

Standard Autolite plugs. Nothing special. Not sure of the temp range but that should not be an issue as it does it cold or hot. Actually worse when it is hot.

 

That sounds like a TFI module issue. Have you pulled the codes recently?

 

sounds like tfi module to me also.

check codes.

check timing with spout out.

reset computer.

 

I have not pulled codes. Do you get codes when the CEL is not on? The last time I tried I could not get any readings. Not sure if it is a bad connect or what.

Also not checked timing but that does sound like what it might be. It runs good, well ok, until you try to give it gas and then it spits, sputters and pops. Basically like what it would do if you had a wire switched. Yep already verified that. Would the TFI cause this?

I miss the old days, points, carb. Duct tape and a screw driver would fix about anything.

What is the easiest way to test he TFI? Also just for the heck of it I unpluged the vacuum brake hose and it ran faster and better. No misses at idle. Hmmm....

 

Yes you can. When you say you didn't get any readings, were you using an actual code reader or the flashing check engine light method? And did you actually get an all-clear code 11 or just nothing at all? This site Ford Fuel Injection has a simple DIY method for reading codes, no special tools necessary.

That's interesting. Did you plug the vacuum hose after disconnecting it from the booster? If so that would indicate a leak in the booster. Do your brakes operate normaly?

 

I was using an actual code reader. It was not getting a signal, nothin. CEL has never come on.

As fo for the vacuum line...I just pulled it off, engine rev increased (normal) and smoothed out. I plugged it with my finger and the engine rev came down and it almost stalled out or at the very least ran with a lope. Brakes do not work normally. Next project....I think I lost the power boost. Pedal goes to the floor, ie manual brakes. Yep I remember those.

One other item. It does have a noticable "tick" coming from the engine. I know that a bent or sticking valve will give some of the same problems.