View Full Version : 74 FJ40 still running terrible... ignition?

08-25-2010, 09:32 AM
It seems like fuel is flowing.. . new pump, new filter. 3lbs of vacuum prior to pump, 2lbs at the carb after the filter...

This thing is running terrible....

Thought it was running out of gas at the carb, because it runs so rough at steady rpm, misses, sputters. Bad initial hesitation upon acceleration.

If I advance the timing, it accelerates great, but still runs rough upon steady rpm going down the road.

timing never seems to stay where I put it, always different when I go back and look. advance too far and it is backfiring through the carb.

compression test yields 130lbs -+ 2-3 lbs on every cyl...

I need to check coil for spark, but think it is there, starts, runs, acclerates...

Distributor is original, new cap, rotor, wires. Points have been replaced with electronic points... vacuum advance seems to work,

where do I look now?! Dang it, I'm missing the summer!


Air Randy
08-25-2010, 10:12 AM
If you want bring it over so we can check it out, it's really difficult to diagnose stuff like this remotely.

If your timing is changing then either the hold down clamp is loose, the distributor gear has busted the pin and is rotating on the distributor shaft, the distributor and/or cam gear is worn and slipping a tooth, the cam/crank timing gears are worn and have slipped. These are listed in the most likely to least likely order. If you have the old style cam timing gears that has a rubber mounted gear, those do eventually go bad and start slipping.

A steady miss is usually not fuel related and is a more likely spark issue, especially since you checked compression and essentially ruled out a bad valve or low compression. Could be a bad spark plug, plug wire, or you could have something goofy going on inside your distributor.

The easiest thing to do is swap in a known good distributor and see what the impact is. By doing this you can rule out a whole bunch of stuff very quickly.

08-25-2010, 11:33 AM
The timing not holding would account for what you are experiencing with the running. in addition to the physical aspects of the distributor that Randy mentioned, I would also expect that an intermittent ground connection for the ignition system might cause the running behavior.

08-25-2010, 11:44 AM
would love an experienced eye!!!!!

I live in Golden, am pretty flexible on schedule... thurs is only day that does'nt work for me, around all weekend....


I'm gonna put on new cap, wires, plugs today... couldn't hurt.

seems to run okay when I advance the timing up the wazoo except I get to the point of the backfiring :(
starts fine...

don't have much of any emissionstuff on here. was running fine until this rough running at steady speed which was instantaneous....


08-25-2010, 11:47 AM
hmmmm put new ground wires from battery to chassis and from battery to engine. helped solve my electrical problems with the dashboard/turn signals/ horn

08-25-2010, 12:00 PM
I had these same symptoms with my 40 last fall. It was a combination of a bad rotor and a bad ground to my electronic ignition box.

08-25-2010, 12:12 PM
Cleaning the battery to chassis and battery to engine grounds is very important, and you will not be disappointed that you did this.

Thinking through the ignition ground; the ignitor should be grounded because it is mounted on a metal bracket which is attached to the metal fender, which is attached to the metal body, which is attached to the metal frame, which is attached to the battery ground - each attachment point could be the source of a problem. To make sure the connection is good and reliable I took a "belt and suspenders" approach to holding my britches up and ran a ground connection directly from the ignitor/coil bracket to the battery.

08-25-2010, 01:10 PM
ignition coil....
1.4 ohms on the primary coil
15,6 kohm on the secondary

shouldn't this be between .7-.8 on primary
10k-11k on secondary??????????????????????

Air Randy
08-25-2010, 11:19 PM
Coils are cheap, replace it if you have doubts. A weak coil would allow easy starting but bad running under load. Be sure and check all of the grounds first though like ricardo said.

08-26-2010, 10:26 AM
I picked up a new Accel coil... My old coil had a higher resistance in the secondary, the new one is withing the spec range.
This seemed to help.

the "missing" is not as pronounced. but it is stilling "missing"...

The mechanical advance is working on the distr. but although I DO have vacuum at the carb TO the distr, It is not advancing the timing upon acceleration.

So, at least THAT is not working on the distr.
It seems to be tight in place and very clean on the inside. has an electronic box in place of points.

What is the function of the "igniter"? Can this be causing a problem? How would I check it?

I think your'e right, may need to try a known good distr....


08-26-2010, 11:34 AM
I had these same symptoms with my 40 last fall. It was a combination of a bad rotor and a bad ground to my electronic ignition box.

That is the ignitor mounted on the fender next to the coil????

Air Randy
08-26-2010, 12:47 PM
I DO have vacuum at the carb TO the distr, It is not advancing the timing upon acceleration.

How are you checking this? Keep in mind if it is a vacuum advance dist it only advances the timing when the vacuum is high (throttle closed). That is why you have to disconnect the vacuum line to the dist and plug it when you are setting the static timing at idle. Then, the only time it will advance the timing is when you are driving down the road and let off of the throttle.

If it is a vacuum retard dist (some toyotas had this) I frankly don't know how it is supposed to work or why they built them this way.

08-26-2010, 01:20 PM
pretty sure had a retard. no pun intended. I think it was an emissions thing. might want to post pics so we can decifer. It should run ok retarded :)

08-26-2010, 04:19 PM
pretty sure had a retard. no pun intended. I think it was an emissions thing. might want to post pics so we can decifer. It should run ok retarded :)

well, I've been running that way for a long time now...:D

08-26-2010, 04:26 PM
that's the set up...

added a new ground ... look like the hot wire runs through the (ingintor?) first, just a wooden dowel thingy with a coil around it? and then to the coil itself...

the only ground for this gray box is the contact to the fender, grounded it again at the screw to the - battery post.

still runs crappy, missing randomly.

08-26-2010, 10:38 PM
I have not worked with the ignition setup that you have. I don't think the silver box is an igniter. I know it does not look like any Toyota igniter box that I have seen. With the photos up, perhaps someone will chime in with what the silver box is.

How advanced is your timing? I don't recall seeing the distributor diaphragm being behind the oil filter like yours is.

Air Randy
08-26-2010, 11:29 PM
Check the gap between the electronic pickup in the distributor and the rotor too

Uncle Ben
08-27-2010, 08:54 AM
The pick up and reluctor look like a Petronix conversion. I had one for years and it worked very well. The "silver thing" is a resistor. That simply reduces the voltage to the coil. I would suspect advance settings and, as pointed out, your distributor is rotated quite a ways counter clockwise so it's probably off a tooth or two.

08-28-2010, 09:46 AM
do I need the resistor if I don't have points?

08-28-2010, 12:31 PM
I have this distributor,

not this one,

which is why it looks like the diaphragm is so wacky.

So, now I realize that I have petronix ignitor which is grounded directly to the coil.

still not sure if I need to run the juice throught the resistor since there are no points. the petronix web site says to measure the volts to the coil and divide by the resitance, not sure my fluke 179 will measure the higher voltage.

I believe that is an advance distr... pulled off vacuum and sucked manually (orally?) and there is no change or movement...
could that be causing the rough running? no vac advance?


08-28-2010, 02:50 PM

If that IS a vacuum retarder, It was plugged into the vacuum at the baseplate of the carb.
I capped it off
And I bypassed the resistor, since points have been replaced with the Petronix ignitor.

Just ran it around the block and put a fresh tank of premium. set the timing to about 12 degrees advanced.

Running much better for a couple of blocks... gonna take it out for a longer drive and see what happens!


Air Randy
08-29-2010, 12:45 PM
That sounds promising! Let us know how it turns out. If you ever decide to replace that old distributor consider getting an HEI unit. MAF now sells them and the prices have come down to around $250. It will drop right in, requires 1 wire to hook up to switched 12V and will give you a little bit of a performance improvement. It will give you a little better advance curve to make it feel peppier. It also allows you to open up the gap on your spark plugs to .050 so you get a cleaner burn.

And, if you ever need replacement parts you can buy them in any parts store in the US since they use standard GM ignition components.

08-30-2010, 10:24 AM
Thanks Randy, Ricardo, Martin, Uncle Ben!!!!!!!!!

Just that little bit of back and forth really taught me a lot. I look forward to the day when I can chime in on someone else's problem...

Being a poor diagnostician means I tried all the little stuff... It seems like the problem was the retarder/advancer. Still not sure which one it is supposed to be and why it was such a big sudden change.

I guess with these old rigs, every little thing makes some difference.

with the retarder plugged off, my timing stays in one place (advances mechanically anyway)...

This thing is now running better than ever except for bogging down on initial acceleration. But runs under load better, fires right up, less backfiring.

Getting lots of hot spark by skipping the ancient resistor (have the pertonix ignitor anyway) and have the timing in one place makes a big difference...

Now, just may be getting the carb jetted correctly for the altitude