I have had a progressively worsening problem with part-full load bucking it seems to be worse when the engine is cold.

I have tested/replaced the TPS.

Now I am leaning on the FI points being the culprit.

How are these tested? What should I look for upon visual inspection?

Any other causes for my symptoms?

here is what I have gone through trying to nail this down:

Ingition improperly set (mine is spot on to factory specs)

Possible malfunctioning vac adv (mine seems to function with suction)

Fuel pump/filter clog (my tank was recently acid bathed and has a new filter and a inline pressure gauge reads normal at idle and revs while sitting).

The main problem I've seen with trigger points is that the rubbing blocks wear down until they don't open up enough anymore. I've got new life out of old ones by bending the contact point arms (the fixed ones) back equally just a little bit. I'm sure there's a spec on what the proper gap should be somewhere....you could set them up accordingly with them installed and the breaker plate removed. To test, hook up a ohm meter or test light and make sure they are making and breaking reliably. A little buff job with some 400 grit (leave NO residue from abrasives) and a good cleaning with contact cleaner (Radio shack) is a good idea. Make sure the dist. cam is clean and lubed with dialectric lube or dist. lube. When you reinstall them, there may be some play in the mounting. Make sure they're centered and seated nicely. I think new ones are still available too. Other suspects may be TPS, MPS, CHT sensors.

Could be lean surge from a bad temp sensor (CHT or IAT).

You might want to check your harness where the wires enter the connector for the points. My harness was very brittle and cracking to the point where two of the wires were down to thin strands. I had been experiencing an internmittent bucking problem as well (mine was when the engine was warm though). I pulled the harness completely out and repaired all of the problem areas, reinstalled and have had no more problems.

QUOTE (lapuwali @ Aug 26 2005, 12:23 PM)

Could be lean surge from a bad temp sensor (CHT or IAT).

I had similar problems that turned out to be the CHT.

Also check your TPS, just disconnect it and try a road test, the engine will be a little sluggish without it, but you can see if the bucking stops or not. It could be an adjustment if it is the TPS

And while I followed the same symptoms, I found a fuel pump relay was not working ON all the time, constantly failing in microsecond bursts, and leaning the mix out... all the time.

If you have a relay with an open cover, you can watch that, and hear it.


M

QUOTE (redshift @ Aug 26 2005, 01:57 PM)

ON M

Great info guys, many of these things I havent though of.

I ruled out the trigger points and distributor

I think it was caused by a bad IAT sensor, it seems to work fine now but I havent driven it much yet

IAT Sensor? you mean cht?

QUOTE (redshift @ Aug 26 2005, 02:57 PM)

And while I followed the same symptoms, I found a fuel pump relay was not working ON all the time, constantly failing in microsecond bursts, and leaning the mix out... all the time. If you have a relay with an open cover, you can watch that, and hear it. M

crapola!

i bet that was my problem.....dude why didnt you tell me

Everything was fresh, new, or rebuilt, except the actual relay. It failed, and worked in such a way, that you'd not hear the pump on-off-on-off-on-off....

You should see THOSE relays do the on-off dance. clickclickclickclickclickclickclick.


M

QUOTE (redshift @ Aug 28 2005, 02:32 PM)

Everything was fresh, new, or rebuilt, except the actual relay. It failed, and worked in such a way, that you'd not hear the pump on-off-on-off-on-off.... You should see THOSE relays do the on-off dance. clickclickclickclickclickclickclick. M

okay miles, what happened to you AIM membership?


did you loose it with the divorce...did the goat take it when she left?

No not the CHT but the thermotime temp sensor, the one on the manifold not the head.

I chanced the sensor Miles but no change, im gonna have to take the top off of one so I can use it to check the others.

I've seen trigger points that looked OK, but did not ohm out within spec. I don't know what the spec is from memory, but there is one. I guess my point is, unless you see something visually wrong there isn't much of a visual test.

Thanks Perry I wasnt sure if there was anything to look for with the FI points.

I drove it t o work this AM and my problem persists and actually seems much worse.


Question>

Does the fuel pressure fluctuate under load (ie. driving) rather than just with an increase RPM's in neutral?

Can I accurately check the fuel pressure with an inline guage by just reving the RPMS?

32ft/lbs is the magic number right?

The fuel pressure should remain pretty constant under all conditions. The fuel rail on the drivers side has a "t" in the line between the injectors. Remove the screw plugging it and hook up your gauge here. Be very sure your hook-up doesn't leak (fire hazard). Around 30lbs. is good. The fuel pressure regulator is adjustable. Something else to think about: Often a motor that runs well under little or no load (light throttle), but craps out when you put your foot down a bit, has a weak spark. When you put your foot down, cylinder pressure increases and it takes more juice to fire it. If your problem seems strictly load related. you might re-check all your ignition system.....plugs, points (gap and/or dwell), cap, rotor, condenser, wires, and resistor ends.

I will give the ingiton system a second look.

Would a failing coil produce this effect?

I took the tank out once for cleaning etc...Put it back and the car would start, run and operate but would buck and stall...

When I put the tank back, I got the fuel lines underneath, kinked and strangling the motor of fuel...

Un-Kinked and everything worked fine from then on...

2-OH!

Mine likes to do the bronco dance as well. I just replaced the fuel pump becuase it failed, and while it's drivable again (mostly at high rpms) it still bucks at lower (3200 and below) rpms when stepping on the gas, not upon decelleration

. It just came back from the shop where they checked the distibuter and the points, timing and dwell, so I'd like to think they knew what they were doing. The car seems to run better when I first start it up.

Tonight I'm going to unplug the TPS so see if that makes a difference, but have a feeling it's something else. Bad injectors maybe? I've already replaced 1 injector that had a cracked head hoping that would improve things. I haven't tested the others....those things are expensive.

Yes Kelly...could be coil too, but this is rather rare. Didn't you say you replaced the TPS? If so, did you re-adjust it properly? If your problem is just at light throttle opening, this could be the cause. Here's a link to a great FI troubleshooting site:Anders' Site

So before I head home from work I give all of the ingnition particulars a look.

Turns out the number 4 wire at the dizzy end was partially loose. sungged it up and that cured it.

This same wire had a problem before I test swapped my dizzzy for a know good one

I really dont think this was my initial problem because I felt a big difference after I changed the IAT. but who knows?

Thanks for the tip Randy it sure made my trip home enjoyable.


When I test swapped my TPS I calibrated and cleaned the one that was on there and then put it back on after I ruled the TPS out.

Anders' site is great for D-jet knowledge thats for sure

ahh...good, glad to help