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  #1  
Old November 9th, 2005, 09:55 AM
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Stupid vacuum hose

OK on the back of the IAC mounting bracket there is a small vacuum hose, where should it go? I am having problems with the engine idleing from 1-2k rpm. If I cover the hole the engine dies at every stoplight unless I rev it, and lacks power from 1-2krpm but from 2k on up the power is fine. With the hole left open at a stop the engine rpms hunts from 1-2500 rpm but the power is better. My problmes may be more then just the dumb hose but at least it's a start.

But so far in trying to find the problem I have, checked: coolent temp sensor, fuel temp sensor, TPS, cleaned the stepper, played with the timming, checked the vacuum pressuer, replaced the coil and some other things I'm forgetting.

The other thing is it takes FOREVER for the engine to warm up, with an outside temp of 35* F the engine only gets to about 180* after about 30 minutes of driving. The odd part, my thermostat opens at 195, it never opened the top hose on the radiator was still cold. My thought is the engine is running rich as I can goose the throttel a few times and get puffs of black smoke out the exhaust.

Maybe there is something wrong with the vacuum advance on the distributer? Also gas milage lately has gone from Suck to Super Suck, I am guessing it's in the 8 to 10 mpg range.

Thanks all!
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  #2  
Old November 9th, 2005, 11:20 AM
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Jeffrey Rosbrugh
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I will check this evening Mike. Should I take a photo too?
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Old November 9th, 2005, 11:31 AM
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Is that the one that comes off the back of the diaphragm? It seems like it hooks around the back of the plenum and attaches to it on the side of the inlet right infront of the butterfly.......
.......I had better look too, but it would seem to make sense judging from your symptoms.
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Old November 9th, 2005, 11:33 AM
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Robert Dassler
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Mike,
The vacuum hose in question goes from the IACV housing to the fuel pressure regulator. When engine vacuum is low, the fuel pressure is raised...so a disconnected vacuum hose will result in a high, hunting idle due to the unmetered air leak, and a richer mixture. Based on your problem, I would also check the vacuum and centrifugal advance mechanisms as well as the thermostat. If the truck is not reaching operating temp after 30 minutes, there is a problem...either the t-stat is stuck open or some debris is stuck in it. This will also cause the truck to run rich as it runs on a fixed map until it achieves closed loop operation. Combine the raised fuel presssure with an open loop condition, and it's probably running extremely rich. If it has been running like this for a while, the learned stepper position may be way off, too. I would check all of these things and then unplug the ECU for a few minutes to allow it to forget it's learned settings, then reconnect and restart. If it has been running really rich for a while, you may also have fouled the plugs.
Rob
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Old November 9th, 2005, 11:55 AM
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I doubt if it is the vacuum advance, but that is an easy one to check with just your lungs--I would describe what you need to do, but it seems wrong to be talking about sucking hoses.

The hose off the plenum at the IAC goes to the little cannister directly underneath it, which is your fuel pressure regulator and the most likely cause of your problem.

Hope this helps.


Dang it Rob! You beat me to it while I was looking up the correct name for the cannister!
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Old November 9th, 2005, 12:19 PM
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Ok, thats were I thought it went, but I have the fuel pressure regulator connected someplace else, the normal place for a 4.0 97 defender. So I think the pressure regulator is being regulated but I might try switching the hoses to see if that makes a differance. I reset the ECU last night, had it unplugged for 20 minutes while I screwed with the belt tensioner. The plugs are a little fouled, I'll have to clean them, but I wanted to try and fix it first. The T-stat might be stuck open, but I once ran without a t-stat and I remmeber the engine warming up faster, but the weather was a little warmer, I'll check it anyway. I am pretty sure the temp sensor is ok, I compaiered 3 different temp sensors on a some ice and they all read very close.

What is a normal vacuum pressure when idleing? I think I was in the 20-22 inHg range.

Oh and this running cool rover thing is new to me I am used to the over heating.
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Old November 9th, 2005, 08:21 PM
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Jason Herring
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Quote:
Originally Posted by Mike Hippert
Ok, thats were I thought it went, but I have the fuel pressure regulator connected someplace else, the normal place for a 4.0 97 defender. So I think the pressure regulator is being regulated but I might try switching the hoses to see if that makes a differance. I reset the ECU last night, had it unplugged for 20 minutes while I screwed with the belt tensioner. The plugs are a little fouled, I'll have to clean them, but I wanted to try and fix it first. The T-stat might be stuck open, but I once ran without a t-stat and I remmeber the engine warming up faster, but the weather was a little warmer, I'll check it anyway. I am pretty sure the temp sensor is ok, I compaiered 3 different temp sensors on a some ice and they all read very close.

What is a normal vacuum pressure when idleing? I think I was in the 20-22 inHg range.

Oh and this running cool rover thing is new to me I am used to the over heating.
Wow, cool running rover? I'll trade ya!
From recent experience I can say you don't even need your vacuum advance connected - I've had to retard the hell out of mine since I had my heads done and they shaved off a bit too much, bumping up my compression and causing detonation. I disconnected the vac advance per suggestion and this, along with 91 octane, has helped the situation. But, I doubt that is your problem anyway.

Running lean causes the engine to run hotter, and running rich causes it to run cooler. But, overall this whole internal combustion process creates alot of heat & I can't imagine that your thermostat is functioning correctly if after 30 mins you are only barely reaching operating temp. The only way the engine can dissapate heat is through the radiator, the heater core or ambient temperature loss from the block. I'm thinking that if you aren't up to your neck in snow and ice, you are getting your cooling from the radiator, and that suggests a malfunctioning thermostat.

Follow-up Post:

You could always try putting cardboard in front of the radiator to reduce it's effectiveness and see if you warm up quicker... that would suggest your radiator is cooling when it shouldn't (eg open thermostat).
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Old November 9th, 2005, 09:00 PM
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Well it gets better I made a few short 2 minute runs to the store and back, it stalled twice, I left it running in the lot for a 10 minutes and it not only warmed up to 180 (E-fans running the hole time) but I drove home and it ran fine the hole way! It is a little warmer out, but it was raining the hole time too.

I am starting to think it's electrical, I'll keep everyone updated Thanks for the ideas so far if anything this will be a great FAQ thread
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