Does a bunch of important stuff. Like and including ignition (I don't have my FSM here). More than likely, if the fuse is blown, the truck wouldn't be running. It's a left field call, but a quick check of all your fuses will rule that out.
egr tube blowout turns ugly & related idle issues
- Thread starter Infinity00
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Does a bunch of important stuff. Like and including ignition (I don't have my FSM here). More than likely, if the fuse is blown, the truck wouldn't be running. It's a left field call, but a quick check of all your fuses will rule that out.
I think the only way you would have a vac leak between the manifolds, where the heat riser is, is if you have a cracked intake. The two gaskets that go between the manifolds and around the heat shield would give you an exhaust leak, if they were leaking. I think; it has been a few years since I have had mine apart.
You said you checked for a cracked intake (below the carb) and didn't see one, so you should be OK.
The reason the intake cracks is because the heat shield or the heat rise fail and the hot exhaust pounds on it, instead of being directed down the down pipe when the engine gets hot.
Bad bushings on the heat riser can be a source of exhaust leak.
Bad gasket on the plate covering the inlet on the exhaust manifold where the j-pipe went could be source of exhaust leak.
Also, there is a check valve on the skinny pipe that connects the ABV/ASV to the down pipe. If that is shot, exhaust can come back up the skinny pipe into the ABV/ASV. But don't worry about that right now.
The little pipe that comes out of the insulator/heat shield that used to have a hose that went to the EGR modulator; did you plug that properly? Possible vac leak there.
From what I understand, the EGR system retards spark or ignition advance requirements. So when you move it, as in a desmog, for the best performance the ignition advance curve on the distributor needs to be adjust (aka a recurve).
You mentioned that you have advance the initial timing and it idles better, but when you drive it up hill it is sluggish. A recurve (once you get all the other components working correctly) might address that.
If no one who knows what they are talking about chimes in on that, after you have convinced yourself that you don't have a vac leak, clogged exhaust or some faulty component (like emissions computer), post a new thread asking for advice on full desmog/ignition advance recurve.
- Thread starter
- #24
Just a quick post to follow up with testing over lunch. Took vacuum tube off manifold from brake booster and applied vacuum pump to the booster side and was not able to pull a vacuum. This probably indicates a bad booster as I should be able to pull a vacuum and hold it. But if I plugged the manifold side (taking brake booster out of system) it didn't change the idle behavior. The accordian thing was replaced and I couldn't see how it is attached and it doesn't look like there is sealant on it where it goes into the manifold. When I carefully sprayed carb cleaner at the base of it, the rpms revved up quite a bit. What is this accordian looking thing? Also the pcv tube is pretty hard and probably should be replaced.
The vacuum reading holds pretty steady now at 15 or 16 inHg dropping down to 13 every once in a while, maybe every couple of minutes or several minutes will go by before it does it.
I'll post more later...thanks for all your help.
The vacuum reading holds pretty steady now at 15 or 16 inHg dropping down to 13 every once in a while, maybe every couple of minutes or several minutes will go by before it does it.
I'll post more later...thanks for all your help.
Can you post a picture of it? Or identify it in the FSM and give it a name?
Does it have 3 small (3mm) vac hose fittings on it and is it screwed into the intake manifold?
Or are you possibly referring to the air intake hose that routes fresh air into the air filter housing?
I really have no idea what you are referring to here.
EDIT: See image on post #28 below
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So, with the engine off, you removed the vac hose that goes between the intake manifold and the brake booster by disconnecting it on the intake manifold side?
Then you hooked up your hand held vac pump to the hose and pumped and it wouldn't hold a vac? There's a bunch of air in there, so getting it all out's gonna take more than a few pumps. But you are convinced that it didn't hold a vac?
Yeah, it should hold a vac until you press on the brake pedal, then it will let some air in.
You mentioned that you measured vacuum on the intake manifold from two different places while the engine was idling.
The first place was off the brake booster. To do this, I assume you disconnected the vac hose that goes from the brake booster to the intake manifold on the brake booster side and then connected the vac gauge to the hose. You noted that the vac reading you got here was low, ~5 inHg, right?
Could you double check this measurement and see if it is the same?
The second place you measured vacuum on the intake manifold while the engine was idling was at this elusive 'accordion' looking thing (which we will soon know the name of, but for now let's enjoy the creative achievement of deciding to call it whatever the hell we want). And the vac here measured ~15 in Hg?
And did you get a chance over lunch to reattach the vac gauge to this second place and take two more vac measurements with the engine idling?
First one with the intake manifold to brake booster hose attached as it normally should be.
Second one with the intake manifold to brake booster hose detached from the brake booster side and the hose plugged.
If so, what were the readings on those two measurements?
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Can you do me a favor and check to see if the tube (vac fitting) on the intake manifold to which the hose between the intake man and the brake booster connects also has a smaller, 3 mm fitting to it? There should be a Y there with a smaller hose that goes the A/C idle up solenoid, if you have AC.
See picture in next post, post #28.
If so, can you unplug that and plug your vac gauge into that fitting?
Then start the engine.
With the engine idling, take a vac reading. What is that reading?
With the engine still idling, remove and let the hose that goes from the intake manifold to the brake booster just hang open and take a second vac reading. What is that reading?
With the engine still idling, plug (on the intake manifold side) where the hose that goes from the intake manifold to the brake booster and take a third vac reading. What is that reading?
See picture in next post, post #28.
If so, can you unplug that and plug your vac gauge into that fitting?
Then start the engine.
With the engine idling, take a vac reading. What is that reading?
With the engine still idling, remove and let the hose that goes from the intake manifold to the brake booster just hang open and take a second vac reading. What is that reading?
With the engine still idling, plug (on the intake manifold side) where the hose that goes from the intake manifold to the brake booster and take a third vac reading. What is that reading?
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See picture below
Is that the accordion thing? Isn't that just a dust boot?
If you sprayed carb cleaner around the base where it meets the manifold, the idle increased?
Sounds like your right, that there is a vac leak there.
- Thread starter
- #29
I'll take the three readings here after I get it going. Yes that is the accordion thing but mine is metal and attaches tightly into the manifold - I wouldn't think of it as a dust boot since all dust boots I've ever encountered are rubber. I took some pics and uploaded but not sure if they've come through. I'll get on a computer later and upload them.
Yeah, give it a try and see what you get. I'd be interested to see the measurements.
Sounds like you found a vacuum leak at the base of that where it ties into the manifold.
After you take those measurements, try the carb spray around the base of that again (after you reconnect the hoses) and see if the idle revs again.
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- #32
Vacuum gauge hooked to 3 mm fitting with car idling but not fully warmed up it 16 in hg at about 1500 rpm. 15 in he at closer to 1000 rpm.
- Thread starter
- #33
Taking the brake booster line off and letting it dangle not plugged, the reading is about 2.5 in hg. Then plugging it the vacuum goes back to 15 or 16
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- #35
Plugging the dangling hose end with a plug, not re attaching it. You were right about the brake booster, I pumped that hand pump 100 million times and I got a vacuum reading of 10 is that held until I pumped the brake.
- Thread starter
- #36
I'll try a pic upload again
Alright, get vac back on it (sorry you're gonna have to get a work out again) and just let it sit there for like 5 or 10 minutes and see if it holds the same vac. Engines not running when you do this right? doesn't need to be
- Thread starter
- #39
I need to run to the store to get more carb cleaner with a straw for more precise aiming. Also I don't have the air cleaner on but hoses disconnected and plugged. I tried to make sure the aerosol didn't go into the carb throat earlier but I think I'll double check with better precision aim and air cleaner assembly on.
- Thread starter
- #40
When you say let it run for 5-10 minutes, does this have to be after spraying that area? If it doesn't, then I know it will drop to 12-13 occasionally then come back up. I have a 30 sec video of that happening but it doesn't happen regularly.
