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View Full Version : 1975 fj40- Emission system help


PhatFJ
11-13-2010, 09:41 AM
Well, I have a question (or 10). I picked up a 1975 fj40, Colorado truck with 75k original miles 99.99% stock. I am the 3rd owner, it has set for years. I was told that the carb was rebuilt right before I bought it (not convinced of the quality of the build). Here is what I have done so far- drained the gas tank, installed new fuel filter, installed new oil pan gasket, new oil and filter, new air cleaner, new points, rotor, cap, plugs and wires, set the dwell, timing and adjusted the valves. Checked the compression, all cylinders around 110 while the oil pan was off, I looked at the cylinders and they look great. The plugs were quite black with carbon when I pulled them. The issue is that it is still idling quite rough. I checked the PCV valve and it seems to be working fine as there is strong vacuum and when I disconnect the hose the idle increases a bunch. I have checked the ports on the VSV and the ones that do have vacuum, have about 10inHg. I have the fsm on the 2f and Chassis /Body but do not have fsm for the emissions, just the Haynes manual which seems pretty vague on this system. Is there a good flow chart available for checking this system and it's components? Any help is greatly appreciated :bowdown:

Thanks, Brian

Phrog
11-13-2010, 11:29 AM
You might need to spring for the emissions manual -
http://www.sor.com/sor/cat223b.tam?xax=27398

-Phrog

PhatFJ
11-13-2010, 12:56 PM
You might need to spring for the emissions manual -
http://www.sor.com/sor/cat223b.tam?xax=27398

-Phrog

Yes I might... I could go here--
http://www.tlc4x4.com/2000/Parts/tlc_books.htm

Thanks

cbmontgo
11-13-2010, 06:52 PM
Brian,

I recently (like this week) had a big idling problem that was due to an intermittent idle solenoid at the carb. I can't remember if the 75s have the solenoid or not; I know the 76+ does.

HTH--

RicardoJM
11-13-2010, 07:27 PM
...The issue is that it is still idling quite rough. I checked the PCV valve and it seems to be working fine as there is strong vacuum and when I disconnect the hose the idle increases a bunch...

Does the distributor have a vacuum hose connected to it? If it does, is the distributor a vacuum retard of vacuum advance? If the distributor is vacuum retard - remove the vacuum hose, plug the hose and see if that improves your idle issues.

... Is there a good flow chart available for checking this system and it's components? ...

I don't have a good source of details for 1975 emissions. Is there a sticker in the hood detailing what should be there?

Rzeppa
11-14-2010, 12:33 PM
Hi Brian,

Lots of carbon normally means it is running too rich. A stock 1975 will generally have the vacuum retard distributor, and at our elevation 7 BTDC static timing is not advanced enough.

You might try advancing to around 11 or so to start - you'll likely hear the RPMs come up right off the bat. Before you do that make sure your points gap is around 0.018". It'll run like crap if it is too close.

Rough idle can also be caused by a vacuum leak. Try spraying carb cleaner around the base of the carb and around where the intake manifold mates with the head. If you hear a change in idle you have found a vacuum leak. You might also check the manifold nut/bolt torque - on a 75 they should be around 33 Ft/Lbs.

Don't forget to check your idle mixture adjustment. The screw is on the base of the carb on the valve cover side. To get to it you have to take the air cleaner housing off. I normally start at about 1.5 turns out, and then go from there. I usually end up somewhere around 2.5 to 3 turns out. This mainly has an effect on idle mixture, but has a slight affect above idle as well. Mainly the jets affect mixture when the throttle is opened up.

One last thing to check for is a crack in the intake manifold under the carb just above where it mates with the exhaust manifold. It is a pain to get to because you have to take the carb off for the visual inspection, but that is a fairly common place to crack. Cracking there is normally caused by the exhaust manifold butterfly either not being there or not closing after warm up. The hot exhaust gasses against the cold underside of the intake makes for quite the temperature difference.

subzali
11-14-2010, 09:05 PM
Brian,

Would definitely recommend making sure your carb is tuned, and like Jeff said advance your timing a little bit more than it is. You should be getting more like 15" or 16" Hg vacuum I think at this altitude (someone who's done this more recently should chime in and verify that for me). It sounds to me like you have a vacuum leak somewhere. Emissions FSM is the shiz for emissions stuff. Your truck should have an idle solenoid too, I think they go back to '68 or even earlier. But having an erratic one is tough to diagnose, props to Carson for solving that one on his! :thumb:

RicardoJM
11-15-2010, 06:55 AM
I probably should have expounded more on my hypothesis of the problem Brian is having. By disconnecting the PCV a large vacuum leak is introduced and with a vacuum retard distributor connected directly to manifold vacuum - the leak allows the timing to advance resulting in the increase in idle speed.

We experienced this a couple of weeks ago when we put the rebuilt carb on Pete's 72. The idle was not stable and the idle adjustment screw would actually kill the engine when we tried to increase the idle. The vacuum was also hovering around 10. When we removed the connection to manifold vacuum - everything improved to where we could dial in the adjustments:thumb:.

Of course, I don't know if this is the situation with Brian's truck - but it should be checked.

RicardoJM
11-15-2010, 07:03 AM
B...You should be getting more like 15" or 16" Hg vacuum I think at this altitude (someone who's done this more recently should chime in and verify that for me)...

I have read the "at least 15 at altitude" but have not hit that mark in my rig. The best I've been able to see is 14, which when adjusted for altitude is within an acceptable range. Here is the source (http://findarticles.com/p/articles/mi_qa3828/is_200108/ai_n8978956/) I found that indicates 1 for each 1K of altitude for adjustment. The F Engine manual FSM indicates a healthy engine has at least 18 (non USA) and 16.5 (USA) of vacuum - so at 5K a desmogged F engine with at least 13 is within spec.

One of my back burner projects is to start a thread where others can post up the vacuum their rigs pull; along with engine information and altitude of where the vehicle was tested.

...Your truck should have an idle solenoid too...

Yes, it will have an idle cutoff solenoid.

Rzeppa
11-15-2010, 09:11 AM
I probably should have expounded more on my hypothesis of the problem Brian is having. By disconnecting the PCV a large vacuum leak is introduced and with a vacuum retard distributor connected directly to manifold vacuum - the leak allows the timing to advance resulting in the increase in idle speed.

Kinda sorta - with factory emissions connected properly, the distributor vacuum diaphragm is connected to the Vacuum Switching Valve (VSV), and the emissions "computer" decides when to apply vacuum to the distributor, which will depend the state of various inputs to the computer.

Instead of disconnecting the PCV valve, disconnecting the vacuum line to the distributor diaphragm will have a much more immediate effect of preventing any timing change due to vacuum, and if the line is pinched shut, then there won't be a vacuum leak through the VSV.

PhatFJ
11-15-2010, 09:47 AM
THANKS guys!! I have not figured out the "multi quote" thing so I will tell you what I have done...
After posting, I went ahead and pulled the carb because I was not convinced that it was done properly. Glad I did, the linkage was not installed correctly and it was good to go back through it and clean things up. I wish I had read your post Jeff regarding the intake manifold before reinstalling the carb but I think if the manifold were cracked it would show up when I sprayed the starter fluid around. By the way I got NO idle change when spraying starter fluid around any of the vacuum lines or carb. I will check the manifold next time I pull the carb. I did advance the timing up to about 10 and double checked the gap to 0.018, dwell is at 34 (FSM says 39 to 40), set idle mix to 1.5 adjusted to around 2-2.5 for now. I was a bit thrown off by the VSV not showing vac on the distributor port but then read that the computer controls when it changed the vacuum.. I did check the throttle solenoid valve and it is working properly, as are the choke breaker and AAP.
After cleaning the carb and re installing it with the linkage set up properly, it is running MUCH better (not perfect yet) but I will pick up the emissions manual and continue to fine tune it... I am VERY grateful for all you help :bowdown: I am excited to keep this an original 1975 with all of the factory systems and components working so THANKS again for all your help, experience, and wisdom!!

Sincerely, Brian

subzali
11-15-2010, 08:50 PM
Brian, the crack that the intake manifold can develop is under the carb, so spraying starter fluid will not get there. You really do have to physically pull the carb off to check it. While you're investigating into that try to decipher whether the valve that redirects exhaust gas to the intake is working properly (i.e. make sure it closes when fully heated so it does not crack the intake manifold).

Good luck on your project!

PhatFJ
11-16-2010, 07:46 AM
Thanks Matt, I will do that.. This brings up an interesting point. I do not think this part of the system is installed as there is no duct from the bottom of the intake to direct the warm air into it and there are two brackets below the carb. I will take a pic and post it.. I did check the valve that redirects warm/cold air into the air cleaner and it is working fine.. I knew that there was supposed to be a duct below it but did not know where it went... I will look into this further but it sounds that I have a missing component... Talk to you soon...

Brian

subzali
11-22-2010, 11:20 AM
Brian,

You can take a look at the diagrams on sor.com which might help you figure out if anything's missing, or posting up a pic will help. I think we might be talking about different things.

The valve I'm talking about is basically right between where the intake and exhaust manifolds bolt together. There is a dowel that sticks through the exhaust manifold with a spiral spring attached to it; that is your heat riser valve and the one that can crack your intake manifold if it sticks in the open position, allowing hot exhaust gases to impinge against the bottom of you intake manifold, under the carb.

It sounds like the other valve you may have taken a look at is part of the EGR system, sending exhaust gases back into the air cleaner (some exhaust is also recirculated back into the air rail). But mine has been disconnected for so long I can't remember how it all goes together.

PhatFJ
11-22-2010, 06:37 PM
Matt, thanks! I realized soon after I posted that we were talking about different things...:o I did check the heat riser flapper and it seems to be loose and in operating condition but I will check the intake manifold next time I pull the carb... I did order a replacement gas tank as the one that was in there was in bad shape so rather than try and repair it I decided to order a new one and get a new sending unit at the same time.. Pulled the whole interior out to check the condition of the tub and front floor boards. They need some attention but I think I can make them work.. also ordered new brake cylinders and will be rebuilding the brakes and knuckles as well.. Timing is everything :lmao: I am still right in the middle of my frame off build on my 70 as well... Anyhow thanks for clarifying the heat riser issue.. before I pulled the tank it was running quite well, I would love to get together and let you here it so I can get another opinion and to let you see if there is anything obvious that I need to pay attention to.. As always, I appreciate your help :bowdown:

Brian

DenCo40
11-22-2010, 07:57 PM
Hi Brian,

Lots of carbon normally means it is running too rich. A stock 1975 will generally have the vacuum retard distributor, and at our elevation 7 BTDC static timing is not advanced enough.

You might try advancing to around 11 or so to start - you'll likely hear the RPMs come up right off the bat. Before you do that make sure your points gap is around 0.018". It'll run like crap if it is too close.

Rough idle can also be caused by a vacuum leak. Try spraying carb cleaner around the base of the carb and around where the intake manifold mates with the head. If you hear a change in idle you have found a vacuum leak. You might also check the manifold nut/bolt torque - on a 75 they should be around 33 Ft/Lbs.

Don't forget to check your idle mixture adjustment. The screw is on the base of the carb on the valve cover side. To get to it you have to take the air cleaner housing off. I normally start at about 1.5 turns out, and then go from there. I usually end up somewhere around 2.5 to 3 turns out. This mainly has an effect on idle mixture, but has a slight affect above idle as well. Mainly the jets affect mixture when the throttle is opened up.

One last thing to check for is a crack in the intake manifold under the carb just above where it mates with the exhaust manifold. It is a pain to get to because you have to take the carb off for the visual inspection, but that is a fairly common place to crack. Cracking there is normally caused by the exhaust manifold butterfly either not being there or not closing after warm up. The hot exhaust gasses against the cold underside of the intake makes for quite the temperature difference.

X's 2 on that one:thumb:

Rzeppa
11-23-2010, 08:37 AM
It sounds like the other valve you may have taken a look at is part of the EGR system, sending exhaust gases back into the air cleaner (some exhaust is also recirculated back into the air rail). But mine has been disconnected for so long I can't remember how it all goes together.

A 1975 federal likely won't have EGR. It was introduced in the 1976 CA spec and was followed by the 1977 federal spec...

The EGR circulates cooled exhaust gases to a large port on the carb when the EGR valve is open. The purpose is to dilute the fuel/air mixture with spent exhaust gasses to reduce combustion temperatures and thus formation of NxOx. It has minimal to no use at our elevation because the thin air prevents combustion temps from getting high enough to form much NxOx in our low compression tractor engines. I learned this from the head guy (forget his name or exact title) at the Colorado AIR program headquarters, where I had to get my non-EGR 1978 FJ45 tested for importation. He was quite a motorhead and took a keen interest in my truck!

subzali
11-23-2010, 09:21 AM
Just looking at SOR.com, it looks like Calif. EGR started in the 1974 model year (9/73) and the Federal started in the 1975 model year (1/75). But I don't know...

Brian, do you have an EGR system on your truck? Maybe you could post some pictures?

PhatFJ
11-24-2010, 06:35 PM
shot of the emissions
http://www.risingsun4x4club.org/forum2/picture.php?albumid=76&pictureid=1280

Close up shot of the warm air port on the air cleaner.
http://www.risingsun4x4club.org/forum2/picture.php?albumid=76&pictureid=1281

By the way I did find an emissions manual on e-bay for about $8.00. Now I will go through each component to verify it's condition... Thanks again for all the help!!

subzali
06-11-2011, 07:30 AM
I have read the "at least 15 at altitude" but have not hit that mark in my rig. The best I've been able to see is 14, which when adjusted for altitude is within an acceptable range. Here is the source (http://findarticles.com/p/articles/mi_qa3828/is_200108/ai_n8978956/) I found that indicates 1 for each 1K of altitude for adjustment. The F Engine manual FSM indicates a healthy engine has at least 18 (non USA) and 16.5 (USA) of vacuum - so at 5K a desmogged F engine with at least 13 is within spec.

<snip>

Just to follow up on this thread a little bit - I'm assuming Brian got things figured out (?)...

I was flipping through the pocket manual last night and saw that for high-altitude engines a vacuum reading of 12.6 in. Hg is acceptable. I haven't found yet what Toyota considered to be high altitude, but I would assume it's something like >6,000 ft.