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Old 08-20-2006, 03:36 PM   #71
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Timing

Quote:
Originally Posted by john hd
according to the "book". haynes manuals have been known to have errors in them!

i would look for an emmissions sticker under the hood and see if it is the same 4 degrees or not. my '88 ran at 0 degrees. worth looking into!

john
Haynes says to look at the Emission sticker and check what it says for timing and if it differs from their number of 4 degrees before TDC, then use what the Emissions Sticker says. I check and they both say 4 degrees before TDC. It checked "perfect"! Bill
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Old 08-20-2006, 04:13 PM   #72
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Not a vacuun leak!

Hey guys, looking at all the test results, something is now nagging at me about continuing to chase after a vacuum leak somewhere as the cause of my fast idle.

Here is what is nagging me: In a system with no problems, at normal operating tempertures and in neutral, the computer looks at all the sensors and calculates that 700 RPMs is the appropriate engine speed and it is able to set and maintain that speed with the IAC partially open, as long as nothing changes. That is the NORMAL condition. If you put the truck in gear, putting a load on the engine, the computer meters a little more gas and opens the IAC a bit and maintains an idle speed of about 600 RPMs. That's the way it is supposed to work.

My system is working EXACTLY like that, except the idle speed is 200 RPMs higher. And to me, this the big CLUE.......we know the computer is not trying to get the idle speed down any LOWER than 900 RPMs with the truck in neutral, because the IAC is still partially open! If the computer wanted the idle speed lower, it would command the IAC to close, even to a full close, to try and get the idle speed down to 700 RPMs. It's not doing that! It's happy with the idle speed at 900 RPMs! Some sensor(s) is feeding it info that makes it think that 900 RPMs is the right speed. It's not a vacuum problem! Why? If you closed off a small leak to the intake manifold, lowering the speed a bit, the computer would open the IAC a bit to offset it, and bring the idle speed right back up to 900 RPMs! That's what all the evidence says!

Am I wrong? Bill
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Old 08-20-2006, 04:18 PM   #73
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Quote:
Originally Posted by lebolewis
Am I wrong? Bill
I don't think so. That's why I posted the list above. After you cross off stuff you have checked, eventually you will get to the end of the list, or find the problem by checking what is good.
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Old 08-20-2006, 06:17 PM   #74
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Conclusion

Been thinking some more......I call that PERSISTANCE.....my children usually refer to it as "hard headedness"! Oh well, sort of the same thing! Well,... not exactly!

Went back over everything. Am now convinced it's NOT a VACUUM leak. What have we overlooked, not counting the Engine Coolant Temperature sensor (ECT), and I will check that at running temp, tomorrow. Got out the Haynes book, re-read everything again...........and we have missed the Manifold Absolute Pressure sensor (MAP)! That could be it! I checked it for a VACUUM leak.....but not for correct operation, electrically! Ah Ha! Haynes says it monitors the intake manifold pressure (vacuum) changes resulting from engine load and speed and sends a voltage to the PCM (computer). The PCM uses the signal from the MAP sensor to control fuel delivery and ignition timing, from closed throttle (high vacuum) to wide open throttle (low vacuum). I will check this tomorrow.

Any takers on this is the blinking trouble maker? Bill
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Old 08-21-2006, 03:33 PM   #75
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End of the trail!

One more time:

Checked the Coolant Sensor resistance at operating temp - checked good.

Checked the electrical performance parameters of the Manifold Absolute Pressure sensor (MAP) - checked good.

Sprayed the TB with carb cleaner - no help.

End of the line. It's just no longer worth the considerable sweat required in this hot weather and the frustration to keep looking for the culprit that is causing this engine to idle 150 RPMs too high! It performs great otherwise. So, I will just live with it until it gets a lot worse, if it ever does, then hopefully it will be easier to find.

I think we have eliminated everything, except taking it to a shop with a scanner to see what the scanner says. Even THAT may not point to the trouble maker. If I have to take it in for some other problem, then I will do the scanner thing. That may be sooner than I thought, my power steering pump was making a "whining" sound this morning when I pressed on the brakes! UGH!! Bill
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Old 08-21-2006, 03:53 PM   #76
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odd that you mention your power steering pump.

on my last tbi vehicle i remember there was a sensor or contact that uped the rpm's when the steering was cranked to either stop. this was done to keep from killing the engine when you tried to stall the power steering pump.

possible culprit?

john
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Old 08-21-2006, 05:17 PM   #77
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Quote:
Originally Posted by john hd
odd that you mention your power steering pump.

on my last tbi vehicle i remember there was a sensor or contact that uped the rpm's when the steering was cranked to either stop. this was done to keep from killing the engine when you tried to stall the power steering pump.

possible culprit?

john
John, where did you see that post where I made comments about the power steering pump? When I sent that post, my last post, it dissappeared and has not shown up on this thread, yet! I wondered what happened to it? Bill
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Old 08-21-2006, 05:45 PM   #78
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Quote:
Originally Posted by lebolewis
John, where did you see that post where I made comments about the power steering pump? When I sent that post, my last post, it dissappeared and has not shown up on this thread, yet! I wondered what happened to it? Bill
Bill,

It shows up as number 75 for me.

Bill
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Old 08-21-2006, 05:47 PM   #79
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bill

you may not see it until you refresh your browser. i see it, post 75 last sentance.

john
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Old 08-21-2006, 07:28 PM   #80
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Website Quirq!!

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bill

you may not see it until you refresh your browser. i see it, post 75 last sentance.

john
John, I've discovered an interesting quirk on the site. There are 3 different Display Modes to view this site. 1) Linear, 2) Hybrid, and 3) Threaded. You will find these in the upper right hand part of the screen, just under the pages indicator. I was using the "Hybrid" Mode and my post was missing.....and it still is in that Mode! I switched to "Linear" Mode and it's there. I ran into this once before. Maybe the website Techs should know about this. Bill
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Old 08-21-2006, 07:37 PM   #81
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John, can you remember where those switches

Quote:
Originally Posted by john hd
odd that you mention your power steering pump.

on my last tbi vehicle i remember there was a sensor or contact that uped the rpm's when the steering was cranked to either stop. this was done to keep from killing the engine when you tried to stall the power steering pump.

possible culprit?

john
John, can you remember where those sensors or contact switches were located? If my Suburban has those, and one of them is defective or closed on, it could indeed be the culprit! I will read the Haynes book on the Power steering pages to see if there is any mention of them. Bill
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Old 08-21-2006, 08:25 PM   #82
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bill,

that's gonna be a tough one, i have not had that truck since '99. i sold the books with the truck.

perhaps you could look for a connector on the steering box and try unplugging it. that is, if there is one to begin with!

just a wild stab!

john
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Old 08-21-2006, 08:34 PM   #83
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Hello lebolewis ,I ran this problem to my friend who owns a shop in town here to swap thoughts .One thing we discussed is the TPS voltage ,his comments were that high or fast idle 454s have been common with the TBI ,and his
recommendations would be to adjust your TPS so that you have .50 volts
only. Then disconnect battery to clear the PCM memory (it will clear on these
vehicals ,after 96 up you need a scan tool to do it.)Drive over 45mph for 1/2 mile or more ,the IAC will be commanded all the way closed for a moment to relearn and will use the TPS also for calibration ,then go back to its position
See then if your idle speed is corrected.I had mentioned the TPS before and you had checked it ,but this is suppose to work to get the PCM to slow down
your idle.I agree that your system appears to be working right and the IAC
is working correctly.The last thought I have is that the PCM Prom
(programmable read only memory) needs to be updated or rather have a recalibration ,GM had troubles ,alot with the proms ,many updates and reflashes ,where you have the PCM rebooted to get different info input
in the Prom .The dealer can reflash the PCM .You may have to just get this done .I have never seen a power steering switch cause a fast idle ,but
at this point john hd may be right ,unplug it ,its in the power steering pressure hose ,and you have hydroboost ,thats why your pump moans when you hit the brakes ,check the fluid level first ,you can add a conditioner to
the fluid to see if it can help the whine. did you try closing off your
IAC air hole ? Last ,Put a vacuum gauge on the engine see what it says.
I still use one regularly to check the engine operation ,valves etc.It should read about 18 to 20" hg vacuum ,if it is incorrect it will cause the MAP sensor to give the PCM incorrect information .Once this gets figured out you will be an expert on this issue .Everything you have done is what I myself and any
good shop would do to resolve the problem .Good diagnostics is key to fixing
any problem .

Scott
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Old 08-21-2006, 10:49 PM   #84
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More stuff!

Scott, thanks for all the info.

1) I read all the pages on Power Steering in the Haynes book, and checked all the components on the electrical diagrams, looking for a reference to the power stering switches mentioned by John hd. I found NONE. I will look tomorrow at all the pwr steering hoses to see if there is a pressure switch somewhere. I doubt there is one on my system.

2) The TPS voltage was .78 volts, with the throttle closed. If it can be adjusted, I will set it to .5 volts, then clear the PCM memory, do the 45mph thing and see what happens. An interesting note...... on all these checks where I have disconnected the device and turned on the ignition to check the voltage from the PCM, Haynes says that a "check engine" light will be set and will have to be cleared. Well, that has not happened on my system. Don't know what that implies!

3) The Haynes book says that I can get the PCM fault codes that have been set by the PCM with a simple shorting wire. The readout will be displayed, one at a time, in the same location on the instrument panel as the "check engine" message. This is an OBD1 system (supposed to be) and a scanner is not required. See Haynes page 6-6. I'm going to try that and see what I get, BEFORE I reset the codes by disconnecting the battery.

4) Yes, I did the IAC plugged test. Engine slowed considerably, but not stalled. It's described in one of my previous posts.

5) I am familiar with computer firmware. I not at all surprised that my PCM codes would be out-dated or have flaws in them. Any idea what the dealer charges for an update? They ought to do it FREE! Crappy stuff they have sold to us unsupecting buyers!

6) If none of the above works, I'll do the vacuum gage check.

......to be continued. Bill
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