Misfire,worse under load...TURTCEL

[TURTCEL]

So I have been experiencing the slightest misfire on my Terc for quite some time now but nothing that caused runnablity issues for me...until today. I have an '85 SR5 and when the car idles it runs pretty darn good, with the exception of a slight pop out of the tailpipe...not like a back fire but more like a lean miss. Then when I went out this morning to the store the car hesitated and stuttered (worst in 2nd gear) to accelerate and hills were the worst. After running like this for a few seconds the car would take off and run ok. It is not an occasional issue anymore but is constant now.

Not sure what the issue was I decided to check some things out. The air and fuel filter are new. There are no vacuum leaks. I put on a brand new spare fuel pump that I had at the house. I also pulled all the plugs and they looked fine. I swapped the dizzy for one that I rebuilt and put on a new vacuum advance. The cap and rotor are new but the wires were a cheaper set that I put on about a year and half ago...one broke a long time ago and I replace it with an old spare one that I kept. I pulled each plug wire one at a time to check for RPM change, which there was so no dead holes. Comp test is 155 across the board.

I have had some issues prior with some of the emissions components so I have removed my EGR system, disabled the EBCV, and disconnected vacuum switch A. These last two components control the carbs ability to lean out the mixture while decelerating. Since I have disabled them my surging at 2000 RPM has gone away but my mileage has gone down hill.

Could I have a fuel delivery issue like a plugged pick sock filter in the tank, burned valve, internal carb vacuum leak, bad plug wire...even though they seem fine, or something I am not thinking of that could cause a misfire/hesitation to the car while driving? It almost has the symptoms of plugged fuel filter while going up hill but it is definitely a misfire though.

Any thoughts would be so extremely appreciated.

Peace

[marlinh]

My first thought is a bad ignition wire or spark plug. You will not notice it at idle but only under load. I take it, the misfire still occurs after swapping out distributors. If you had a burnt valve, the engine would not idle smooth.

We used to find bad plug wires by spraying them with water. Amazing light shows in the dark.

I think if the filter in the tank was plugged you would not get the acceleration to smooth out after the initial miss. You would have fuel starvation symptoms that would be more prominent.

[dlb]

gradually worsening and hesitation/backfire under load definitely sounds like fuel filter to me. have you replaced it recently? give it a try, they're only $5 and take a minute to swap.

[TURTCEL]

Fuel filter is brand new. Yes, the hesitation still continued after the dizzy swap.

Timing is fine too, no concern with the timing belt skipping a tooth on the gears or anything like that.

Peace

[dlb]

oops, sorry i only saw fuel filter mentioned in your first post now. could still be the problem if the car sat for a while before it became your DD though—the gas tank may be rusty internally which can cause premature fuel filter failures.

does this only happen when the engine is cold or hot or does it always happen?

a little off topic but when did you disconnect vacuum switch A and disable the EBCV? i'm not sure how cold it is where you are but i've been tracking mileage on several vehicles for almost a year now and have noticed that temperatures and weather have a huge impact on fuel economy, as much as about 15%.

[TURTCEL]

The car has been my daily driver since I got it about a year and a half ago. I disabled the components about 4 months ago on the EBCV and about 10 months on the vacuum switch A. Mileage went from 28 mpg to 20 mpg....ouch.

Peace

[keith]

accelerator pump

[TURTCEL]

accelerator pump

That has crossed my mind. I have noticed that the boot on the accelerator pump is wet sometimes after running, but I thought it may just have been residual carb cleaner that had not yet evaporated. How can I determine if it is actually bad?

A bad accelerator pump would cause symptoms like I am describing then? I have heard they can cause dead spots during acceleration so I am going to look in to that further.

Peace

[dlb]

to test the accelerator pump, remove the air filter housing lid, hold the choke open, and look down the passenger side barrel. open the throttle up all the way and you should see a stream of gas shoot into the barrel. if it doesn't, or it just trickles, the pump is bad.

[TURTCEL]

I did the accelerator pump test and it shoots a nice stream of fuel with no concerns of it not doing that correctly. Guess it is ok.

One thing that comes to mind is that my carb does not have the little check valve on it that is inline in the vacuum hose on the back of the carb (side that faces the firewall). I am not sure if this has been a problem for me for a long time or if it even affects the system, but I wonder if the valve lowers the vacuum going to vacuum switch A? The reason why I disconnected switch A was because the vacuum port on the metal rail that connects to the switch is a very high vacuum...unlike 3 other Tercs that I have checked which their vacuum at that port was much lower.

High vacuum at the switch causes it to lean the carb at the wrong time. I pulled a valve off of a car at the pick n pull and tried it but it seemed bad to start with. It caused no change, but it was completely plugged so I am guessing the test needs to be redone with a good valve to determine if it is the culprit. Any thoughts on this being a possibility?

Peace

[TURTCEL]

A dang vacuum line pulled off of my HAC which make a gnarly vacuum leak at the carb. Fixed.

Peace

[marlinh]

Was that your problem all along?

[irowiki]

Almost sounds like mine was doing! Turned out to maybe be a busted PCV valve.

[TURTCEL]

Was that your problem all along?

Embarrassing to say, but yes. it was from nothing that I did myself. Ironically the hose was a little on the short side so it was stretched to the limit and a little bit hardened. It made it not stay on the HAC port and it must has vibrated free while driving, since it started all of a sudden while I was driving.

irowiki: I definitely believe that if you had a bad PCV valve that you could have symptoms like you described. I had an older Toyota pickup that had a broken PCV valve which was causing excessive crankcase pressure and made the engine fight itself internally which made it run like crap. Sometimes the small things can be the simplest fixes...unfortunately most of us dump a bunch of money into something before finding out it was, oh I don't know let's say a vacuum line pulled from a HAC...haha.

Peace

[Petros]

often when faced with what seems like difficult problem to solve many people jump right to replace major components at great expense. I even remember one newbie on this form that had a bucking engine, his is first thought was to replace the engine. Way too much work AFAIAC, and likely not to solve the problem.

Usually it is more work to isolate the problem than to actually fix it, as you found, the fix is quite often something simple.

That is why I always advise to diagnose the problem BEFORE you try and fix it.