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Sorry, my brain floated away. This was a problem I had with a 3.3l Toyota Highlander. The concept is valid but the 2.2l S10 doesn't have two banks of cylinders.
"There is a 1/2 inch tube on the underside of the intake plenum that goes to the rear valve cover passenger side. It causes a major vacuum leak, but that would cause high +18 fuel trim (too lean). It is easy to miss because it is hard to see."
 

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Discussion Starter #23
So I was able to do the fuel pressure test and leak down test this evening, sill haven’t got ahold a code scanner to read the MAF.
Fuel pressure:
Prime: 37 PSI
Running: 40 PSI
Leak down: held pressure at 40 PSI

Leak Down Test: applied 90 PSI
Cylinder 1: 84 PSI (Crankcase) maybe a little from intake
Cylinder 2: 86 PSI (Crankcase)
Cylinder 3: 88 PSI (Crankcase)
Cylinder 4: 88 PSI (Crankcase)


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If your vacuum is 6 psi, you have a major leak. Pinch off the booster hose and see if it idles better.
 

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Discussion Starter #25
Thanks, I will give that a try in the am, to test my vacuum I’m just using a T adapter near the vacuum canister attached to the hood and a vacuum pump. Is there a better spot I can use to test? The truck now has started to want to die while sitting at a stop sign or red lights, but not all the time, and you sill have to press the gas pedal for it to start sometimes.


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To check vacuum, you tap a vacuum gauge into a vacuum line off the throttle body while the engine is running. You don't use a vacuum pump.
 

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So, Injectors are holding. Pressure while running (assume at idle) is higher than prime (zero vacuum). When running at closed throttle idle, ie. max manifold vacuum, the fuel pressure regulator should reduce the fuel pressure by up to 10". So put the fuel gauge back on and disconnect the vacuum line to the fuel pressure regulator. Use your hand vacuum pump to pull 18" of vacuum to the pressure regulator. A decelerating engine can often go above 20" if vacuum, by the way. It should show a readable change in fuel pressure when you go from no vacuum to full vacuum. If there is no change, your fuel pressure regulator is likely bad, but keep in mind you are still only getting 6" of vacuum from the engine. As far as I know the S10 does not have a vacuum pump. Engine manifold supplies the pressure for the power brakes and has a check valve at the power brake booster to maintain brake vacuum at low manifold vacuum. Check with your vacuum. Pull that and block it off on the engine side and see if manifold vacuum goes up. :mad:You might have a leaky brake booster. That could be large enough a leak and not be found with the standard techniques. Manifold vacuum also supplies the heater and AC doors. At check valve is there to keep the doors from flapping when you accelerate. But it is small. The brake booster is a huge vacuum line. The S10 has a Manifold Air Pressure MAP in addition to the MAF. The Map sensor is basically a vacuum gauge that gives a readout on the scanner from 1 to 5 volts DC.
Your leak down results do not seem outrageous. Probably normal from the rings.
When you get the scanner the first thing to look at is the Long Term Fuel Trim LTFTR and Short Term Fuel Trim STFTR. They indicate injector pulse length and normally both should be -5 to +5. Also of interest is the o2 reading sensor one should fluctuate between 100mv and 900mv fairly smoothly. 100 mv is lots of o2 in the mixture (lean) and 800 is little oxygen in the mixture. The second o2 sensor is checking catalyst efficiency. Should be around 740mv fairly steady but will vary. If the second sensor is around 100mv, check the gasket from the cat to the exhaust pipe.
 

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Oh, Diesel engines have vacuum pumps for the brakes and AC systems. Older engines had AIR Air Injector Reactor pumps for emission controls that were mistakenly sometimes referred to as vacuum pumps.
 

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Discussion Starter #29
I went and picked up an actual vacuum gauge hooked it and it read 7in of vacuum. I unplugged the tube going to the brake booster while it was running and plugged it up, no change in vacuum. I pulled the check valve for the booster and it is working properly. I replaced the fuel pressure regulator and it did fix the hesitation the truck was having when taking off from a stop.
I sill need to pick up a scanner so I can check all the live data. Now it has started almost die if you stop at a stop sign/light and you have to feather the pedal to keep it going. Could a faulty PCV valve cause a loss it engine vacuum? Would the IAC be the culprit for the truck wanting to die after it’s warmed up?


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Glad to hear the pressure regulator helped? Did it fail the vacuum test? There is no PCV 2.2 PCV location for 1999. When I did my head gasket a few months ago I looked for a way to mess it up an could not. It's an air passage restriction built into the valve cover. In the early days of Computer Command Control, before scanners, I used a Digital Volt Ohm meter and paper clips to test with. I would put the car in gear (automatic) and goose the throttle and watch for how quickly it regains a steady idle. With a manual trans, cut the steering wheel to the end stops and use the load from the power steering. Found this How To: New Iac Valve Replacement How To: New Iac Valve Replacement!.
EGR valve stuck open would be a major vacuum leak, if yours has an EGR valve. I suspect Calif emission vehicle don't have one and Fed emissions do. Mine is a '98 Calif although in Florida. It's at the back drivers side of the valve cover. My Calif emission only has a cover plate to block the EGR port, could be that gasket leaking internally? It would be like a stuck open EGR valve if bad enough. RTV Red works well here. The scanner or the engine emission sticker will show Calif or Fed.
 

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Discussion Starter #31
I went and picked up a new PCV valve today, they are cheap only 2 bucks. My truck has one and it’s located on the front of the valve cover near the throttle cables, held in by a plastic nut sorta thing. I did a vacuum test after that and sill no change. The IAC Valve has been cleaned but I have heard they don’t ever really go bad just get gunned up with carbon. Does anyone know of a way to actually test them, I looked online but there wasn’t a for sure way that I could find. I don’t know why the truck would only want to shut off when it’s warm and only while idling, unless it’s the IAC. Next I just need to get the scanner so I can check all the fuel trims, O2 sensor and MAF data.


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4. Reconnect electrical connector
5. Reset IAC Valve pintle position:
A. Disconnect negative battery cable for at least 10 secs
to clear PCM Memory.
b. Reconnect negative battery cable
c. Start engine and check for proper idle operation.

EGR valve? I think the scanner will show IAC activity. Also the scanner will show Throttle Position Sensor, Intake Air Temp, MAF, MAP, Coolant temp. A frayed sensor wire. Whatever it turns out to be will solve the low vacuum. Look where hands have been. It is always something simple and obvious once it is found.
 

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So, I finally got around to checking the vacuum on my '98 2.2l. It is 16" of vacuum at idle. Memory tells me my compression was around 130. I had a coolant leak from the freeze plug behind the flywheel that I could not verify, so for $20 in parts I decided to change the head gasket and hope. Then I paid a shop to pull the tranny and do the freeze plug and clutch anyway. If you have the heater core blocked instead of looped it will change your temp sensor reading affecting the computers calculations. Pulling the brake booster line causes a surge in idle while the ecm adjusts. The vacuum continues to maintain at 16" and will go above 20' on deceleration. The Chevy 2.2-liter will create 125 to 160 pounds-per-square-inch. Which begs the question: what is the "good" compression on yours? From the leakdown test mechanically it seems the engine is sound. The booster vacuum check pretty much eliminates a leak as the cause of low vacuum regardless of source. I think that Hillbilly 3181 is right about valve timing. So here is the scenario: The poor idle hesitation and miss, from the beginning, was the fuel pressure regulator. We don't know the vacuum reading prior to the head job. We don't know how much was shaved or even how many times it has already been done. We don't know the compression change before and after. So the valve job may have caused a new issue. My course of action would be to check compression, disconnect the exhaust manifold from the head and check compression (still possible the exhaust is clogged) then try a head shim or double gasket (shaky but may solve the problem). The MAP sensor reading would double check that the low vacuum gauge reading isn't just something clogging the port you use to measure. Blockage on the intake side would cause poor air flow but not lower vacuum. Does the vacuum fluctuate or is it steady and low? Fluctuate would indicate individual cylinders.
" On overhead cam engines, milling too much metal off the face of the head changes the installed height of the head and retards cam timing. On a pushrod head, it will alter the valvetrain geometry and may require corrections in the length of the pushrods. The only way to restore lost head height and combustion chamber volume is to use a copper or steel head shim with the head gasket, or replace the head." Resurfacing Cylinder Heads & Blocks? Mistakes to Avoid
 

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I haven't thought this out at all, but I wonder what would happen if you simply retard the cam timing via the timing chain a degree or so. The shorter deck should increase compression ratio, the valves are opening earlier and wider. If the computer uses crank sensor for ignition timing and cam sensor for injector timing you could end up with more horsepower.
 

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Discussion Starter #35
Update, I replaced the IAC Valve and the truck seems to idle better for awhile. I can start it up and it’ll sit and idle pretty smooth, but not perfect for a min or so. Then I drive it around and get it warm, when I go to stop at a red light/stop sign, it will sputter and die, I’ll have to feather the gas. I don’t know if it’s only doing it once it gets into closed loop or not, I just ordered a Bluetooth scanner and should be here on Thursday, I will get the sensor data from it and post it as soon as I can. The whole retarding the valve timing, I would have to take it somewhere to have that done, it not that confident in my mechanic skills yet ha. I appreciate the input everyone.


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Discussion Starter #36
So I got my scanner today, I let the truck run for a few minutes to get up to operating temperature and this is the numbers I got.

Long Term Fuel Trim: 2.3
Short Term Fuel Trim: -28
O2 sensor 1: 0.010 - 0.870 Volts
O2 sensor 2: 0.480 - 0.840 Volts
MAP Sensor: 29.2 - 22.7 InHG

The 02 sensor 1 was all over the place, up and down.


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Discussion Starter #38
Should sensor 2 also be jumping up and down? It was just steadily climbing?


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It shouldn't jump up and down, it should stay steady. This is how the computer determines catalyst efficiency. The downstream sensor shouldn't affect driveability at all, but if it fails there will be a check engine light for catalyst efficiency or downstream oxygen sensor.
 

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Discussion Starter #40
Ok, so the o2 sensors seem to be functioning properly. What would be causing my Short term fuel trim to hit -28?


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