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Fluctuating Timing, Loping Idle, Erratic Surging acceleration & Coughing


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xJohnDoe001x
User

Sep 15, 2013, 4:58 PM

Post #1 of 27 (4168 views)
post icon Fluctuating Timing, Loping Idle, Erratic Surging acceleration & Coughing Sign In

Friend, I'm at my wits end. The only thing have not tried is the only thing I can think of at this juncture, a stick of dynamite and a cyanide tablet, a murder/suicide of sorts.

On my '90 GMC with a '91 5.7L TBI I have a very difficult loping idle, delayed and surging acceleration, coughing. After reaching optimal temperature if I switch the engine off and restart it it revs high like a cold start but comes down quicker which is in sync with the timing being advanced a couple of degrees after I start the warm engine then returns to the set timing mark. When I push the throttle the RPMs don't rise quite quick enough and comes down slowly.

I noticed that the idle loping is in sync with timing fluctuations of about a degree, about half over and half under the set timing mark.

When I drive it there is a delayed response then erratic acceleration and coughing which almost shuts the engine down. Probably a different issue but second gear shift at a very late 15 MPH and third is also late at 35 MPH.

Just about everything is new
● MAP Sensor
● EGR Valve
● EGR Solenoid
● IAC Valve
● TP Sensor
● ES Control
● Knock Sensor
● ECT Sensor
● Ignition Coil
● Pick Up Coil
● Plugs
● Distributor Cap
● Rotor
● Timing Chain kit
● Fuel Filter

Things that I have checked:
● Fuel Pressure 10psi (9 - 13psi range)
● COs is 160 but should be 20
● HCs is 2.95 but should be 2.00
● Nox was 0.34 well below the exceptible 4.00
● Compression 118 - 120psi (lowest must be 75% of highest)
● Reset IAC Valve (per Chilton manual 28624 page 5-12)
● Set timing to 0 TDC (per under hood label at AutoZone. Com, mine is gone)
● Plug Wires Resistance (good)
● Check for Vacuum Leak (poured a gallon of water around intake & TBI)
● Check Injector Spray Pattern (good)

What can I do to get this tam druck running good
Sincerely xJohn Doex
Fgghjggffgh


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Sep 15, 2013, 5:21 PM

Post #2 of 27 (4161 views)
Re: Fluctuating Timing, Loping Idle, Erratic Surging acceleration & Coughing Sign In

Have you checked for EGR leakage? I think you may have an aluminum base plate with exhaust ports that was known for rotting out and leaking exhaust to the intake.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



xJohnDoe001x
User

Sep 15, 2013, 8:28 PM

Post #3 of 27 (4147 views)
Re: Fluctuating Timing, Loping Idle, Erratic Surging acceleration & Coughing Sign In


In Reply To
Have you checked for EGR leakage? I think you may have an aluminum base plate with exhaust ports that was known for rotting out and leaking exhaust to the intake.

Yes, the intake manifold is aluminum, so how do I check for an EGR exhaust port leak?
Fgghjggffgh


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Sep 16, 2013, 2:46 AM

Post #4 of 27 (4136 views)
Re: Fluctuating Timing, Loping Idle, Erratic Surging acceleration & Coughing Sign In

So, you have an aftermarket intake? You still need to check the EGR valve itself. You might also want to smoke the intake. Your water method can miss a lot.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



xJohnDoe001x
User

Sep 16, 2013, 12:59 PM

Post #5 of 27 (4125 views)
Re: Fluctuating Timing, Loping Idle, Erratic Surging acceleration & Coughing Sign In


In Reply To
So, you have an aftermarket intake? You still need to check the EGR valve itself. You might also want to smoke the intake. Your water method can miss a lot.

I don't think that this is an after market intake manifold, I sort of remember checking the numbers. It look just like a SBC OEM manifold, check out these links to pix of it:
https://skydrive.live.com/...9C5207%21739&v=3
https://skydrive.live.com/...9C5207%21740&v=3
https://skydrive.live.com/...9C5207%21741&v=3

Now about that smoking thing, yes smoke would be better to displace the air, like a welding shield. How do I apply the smoke? A bee smoker what comes to mind. Let me guess, a special, expensive gizmo?

I know that the top & front of the manifold don't leak for I had a river an inch deep on it. When I said I poured a gallon of water it I was most liberal.
I am 80% sure there is no vacuum leak but to be sure I will revisit that possibility.

Let's please consider other possible causes

That timing fluctuation may be a clue
Fgghjggffgh


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Sep 16, 2013, 1:23 PM

Post #6 of 27 (4122 views)
Re: Fluctuating Timing, Loping Idle, Erratic Surging acceleration & Coughing Sign In

Those links require a password and not accessible.

Water is not a good way to look for vacuum leaks, You need something that enriches the mixture, besides it can't find a leak on the bottom part of the intake gasket.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



xJohnDoe001x
User

Sep 16, 2013, 1:30 PM

Post #7 of 27 (4118 views)
Re: Fluctuating Timing, Loping Idle, Erratic Surging acceleration & Coughing Sign In

How do I do that? One of those Cooper pipe soldering torches, unlit of course, comes to mind.
Fgghjggffgh


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Sep 16, 2013, 2:35 PM

Post #8 of 27 (4116 views)
Re: Fluctuating Timing, Loping Idle, Erratic Surging acceleration & Coughing Sign In

You can use brakekleen or carb cleaner but that still won't find a leak from below. You need to smoke test it to be sure.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



xJohnDoe001x
User

Sep 17, 2013, 12:03 PM

Post #9 of 27 (4096 views)
Re: Fluctuating Timing, Loping Idle, Erratic Surging acceleration & Coughing Sign In


In Reply To
You can use brakekleen or carb cleaner but that still won't find a leak from below. You need to smoke test it to be sure.

So I need to displace the air in the crank case to check for a lower manifold vacuum leak, makes sense.

so how do I do that?
Fgghjggffgh


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Sep 17, 2013, 12:11 PM

Post #10 of 27 (4095 views)
Re: Fluctuating Timing, Loping Idle, Erratic Surging acceleration & Coughing Sign In

Why not try to find if it's up top first. The carb cleaner/BrakeKleen if you hit a spot that should be holding vacuum and engine while idling changes completely that's a trouble spot is the idea.......

T



Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Sep 17, 2013, 12:44 PM

Post #11 of 27 (4090 views)
Re: Fluctuating Timing, Loping Idle, Erratic Surging acceleration & Coughing Sign In


Quote
So I need to displace the air in the crank case to check for a lower manifold vacuum leak, makes sense.


I said nothing of the kind. I said you need to have it smoke tested.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



xJohnDoe001x
User

Sep 17, 2013, 5:53 PM

Post #12 of 27 (4084 views)
Re: Fluctuating Timing, Loping Idle, Erratic Surging acceleration & Coughing Sign In


In Reply To

Quote
So I need to displace the air in the crank case to check for a lower manifold vacuum leak, makes sense.


I said nothing of the kind. I said you need to have it smoke tested.


I'm sorry, I didn't say you said that, I was extrapolating, I thought. You mentioned checking the bottom.. .. .. never mind, How do I do that.
Fgghjggffgh


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Sep 17, 2013, 5:55 PM

Post #13 of 27 (4083 views)
Re: Fluctuating Timing, Loping Idle, Erratic Surging acceleration & Coughing Sign In

This is the third time I'm answering that. With a smoke test.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



xJohnDoe001x
User

Sep 17, 2013, 6:17 PM

Post #14 of 27 (4077 views)
Re: Fluctuating Timing, Loping Idle, Erratic Surging acceleration & Coughing Sign In


In Reply To
This is the third time I'm answering that. With a smoke test.

Dude, I never heard of a Smoke Test, so I was asking
"How do I do a Smoke test"?
Fgghjggffgh


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Sep 17, 2013, 6:22 PM

Post #15 of 27 (4076 views)
Re: Fluctuating Timing, Loping Idle, Erratic Surging acceleration & Coughing Sign In

Unless you have a $1200 smoke machine, you don't do it yourself. You will have to have it done. The machine pumps smoke into the vacuum system at a very low, regulated pressure after capping off the intake snorkel and you look for the smoke. You restrict the PCV and look for smoke in the crankcase or anywhere else vacuum can leak.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



xJohnDoe001x
User

Sep 17, 2013, 6:36 PM

Post #16 of 27 (4070 views)
Re: Fluctuating Timing, Loping Idle, Erratic Surging acceleration & Coughing Sign In


In Reply To
Unless you have a $1200 smoke machine, you don't do it yourself. You will have to have it done. The machine pumps smoke into the vacuum system at a very low, regulated pressure after capping off the intake snorkel and you look for the smoke. You restrict the PCV and look for smoke in the crankcase or anywhere else vacuum can leak.

Will a vacuum leak cause the timing to fluctuate?
Someone suggested I look at the magnet that is just below the rotor in the distributor for cracks and mine was damaged so I bought a new distributor and that smooth things up but not all.
Fgghjggffgh


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Sep 18, 2013, 2:53 AM

Post #17 of 27 (4064 views)
Re: Fluctuating Timing, Loping Idle, Erratic Surging acceleration & Coughing Sign In

Quote">>Will a vacuum leak cause the timing to fluctuate? <<"

Actual manifold vacuum is a primary measure of the load on the engine. The engine is constantly calculating several factors to adjust timing, amount of fuel to deliver and when to shift taking in all info as it sees it and has long before anything much electronic which simply is much faster and efficient if accurate. Bad info because of a failure like a vacuum leak would be one. It just needs to be ruled out as a cause or fixed if one is found. If not move on.

1991 isn't going to just magically tell you exactly what you have to diagnose it like about anything. Dumping water over this wasn't such a smart move. Now what new problem could that have caused?

Seems you are running around in circles and maybe some hands on help would save you a ton of grief. Parts tossing just doesn't work well if they were free because then you need to question the replacements being NG at some point,

T



Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Sep 18, 2013, 2:56 AM

Post #18 of 27 (4060 views)
Re: Fluctuating Timing, Loping Idle, Erratic Surging acceleration & Coughing Sign In

Something is causing an RPM fluctuation. RPM fluctuation will trigger timing change.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



xJohnDoe001x
User

Sep 18, 2013, 9:11 PM

Post #19 of 27 (4041 views)
Re: Fluctuating Timing, Loping Idle, Erratic Surging acceleration & Coughing Sign In


In Reply To
Something is causing an RPM fluctuation. RPM fluctuation will trigger timing change.

Then I must look into getting my truck smoke tested, it's not likely but indeed possible I made a mistake when I cleaned and put new gaskets on the intake manifold. Or the torque wrench I used malfunctioned.

Anyway, till I get that done what should I check if there's no vacuum leak?

My truck does not have an under the hood label so I was looking at a gang of them at AutoZone, some from CA, MT, Federal and not marked. They all had zero degrees BTDC but some said set timing in Neutral others Park and some Either. I going to check my timing both to see if there is a difference.
Fgghjggffgh


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Sep 21, 2013, 8:12 AM

Post #20 of 27 (4020 views)
Re: Fluctuating Timing, Loping Idle, Erratic Surging acceleration & Coughing Sign In

With a different model year engine (could be identical) if factory stickers were available it's messed up now IMO. If all you digging found the setting to be the same that's good enough for and I won't go hunting myself.

The vehicle's VIN could be of some help. It's kind of old to get replacement OE stickers but not sure. I needed just one once and managed to print it out, paint the paper with clear engine enamel and it did last. Auto body shops should do that if radiator support where most are was replaced for some reason get new ones.

IDK - it's old and not original now what more to do on that part?

Thread has lead to finding or ruling out a vacuum leak quite a bit and the issue might not even be that. So much has been messed with it could be something else too so it's still in a diagnosis mode to fix this as I see it.

Hard to say but you could also have a defective new part. Again IDK but I'm not convinced the distributor is right either?

This is tough. You have to rule things out and so far seems just throwing parts at it. Out of this for ages now but the little I do see the replacement parts I have seen and done for myself plain stink compared to OE even at dealerships for the vehicle maker.

The good news is it sure seems stuff is out there for trucks and special interest vehicles for a looooong time - lots older than this,

T



xJohnDoe001x
User

Sep 21, 2013, 10:29 AM

Post #21 of 27 (4008 views)
Re: Fluctuating THINKING, Loping MEMORY, Erratic Surging STUPIDITY & Coughing Sign In


In Reply To
With a different model year engine (could be identical) if factory stickers were available it's messed up now IMO. If all you digging found the setting to be the same that's good enough for and I won't go hunting myself.

The vehicle's VIN could be of some help. It's kind of old to get replacement OE stickers but not sure. I needed just one once and managed to print it out, paint the paper with clear engine enamel and it did last. Auto body shops should do that if radiator support where most are was replaced for some reason get new ones.

IDK - it's old and not original now what more to do on that part?

Thread has lead to finding or ruling out a vacuum leak quite a bit and the issue might not even be that. So much has been messed with it could be something else too so it's still in a diagnosis mode to fix this as I see it.

Hard to say but you could also have a defective new part. Again IDK but I'm not convinced the distributor is right either?

This is tough. You have to rule things out and so far seems just throwing parts at it. Out of this for ages now but the little I do see the replacement parts I have seen and done for myself plain stink compared to OE even at dealerships for the vehicle maker.

The good news is it sure seems stuff is out there for trucks and special interest vehicles for a looooong time - lots older than this,

T

I am so embarrassed and disgusted with myself to say what broken, the "owner".
Hundreds of dollars and all that was wrong was the timing was off.
First the Chilton manual clearly said check under hood label, I didn't have one so I set it to the setting listed most for 5.7L in the manual just to see how it would run then was doing other things while under the hood and forgot about the "Check Under Hood Label"
Second, when I finally got back to the "Check Under Hood Label" I had just emptied the magazine(wallet) to my Parts Machine Gun and slapping another clip in it. I misinterpreted what the label meant when it said, "before setting the timing disconnect the one wire connector, do not disconnect the four wire connector" I thought it meant some models have four wire connectors and some have one wire connectors so just set the timing on four wire models.
I found the one wire connector, it now runs good.

Besides being an idiot, I have an excuse, I live with (if you call it living) ultra super chronic pain and chronic insomnia which caused a host of other mental afflictions not limited to but including severe depression, difficulty absorbing and retaining information, memory lapse, I forgot the rest. The permanent ringing in the ears don't help.

I just failed the emissions test
● HC 0.74. Max. 2.00
● NOX. 0.49. Max. 4.00
● CO. 20.33. Max 20.00
I failed CO by 0.33, anyway I already bought a catalytic converter that I haven't yet installed but tried to see if I can get a refund. I get to retest free.
Fgghjggffgh


Tom Greenleaf
Ultimate Carjunky / Moderator
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Sep 21, 2013, 10:56 AM

Post #22 of 27 (4003 views)
Re: Fluctuating THINKING, Loping MEMORY, Erratic Surging STUPIDITY & Coughing Sign In

I say you are good just got the test too early after it running poorly for a while now. Here you get 30 days for a retest and fine to drive legally if all other items tested were fine like safety items throughout.

CO is lowered by cooling combustion temps which an EGR can do. Again - too early if now running fine give it a good run.

Caulk it up to now an expensive learning thing if all is running fine you did succeed.

Sorry for medical issues. We aren't here for that but I wish you luck with fixes for those issues.

With the truck despite the extended effort you won. Give yourself some credit for that!

Be well,

Tom



Discretesignals
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Sep 21, 2013, 12:02 PM

Post #23 of 27 (3992 views)
Re: Fluctuating THINKING, Loping MEMORY, Erratic Surging STUPIDITY & Coughing Sign In

Tom, not trying to insult you in any way, but isn't high CO caused from incomplete combustion? High NOx is caused from excessive combustion chamber temperatures which EGR cools down to reduce NOx emissions.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Sep 21, 2013, 12:02 PM)


Hammer Time
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Sep 21, 2013, 1:34 PM

Post #24 of 27 (3984 views)
Re: Fluctuating THINKING, Loping MEMORY, Erratic Surging STUPIDITY & Coughing Sign In


Quote
Tom, not trying to insult you in any way, but isn't high CO caused from incomplete combustion? High NOx is caused from excessive combustion chamber temperatures which EGR cools down to reduce NOx emissions.


True

The way I've always explained it is

CO is "burned fuel" (rich mixture)
HC is "unburned fuel" (incomplete combustion)



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
Ultimate Carjunky / Moderator
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Sep 21, 2013, 3:00 PM

Post #25 of 27 (3978 views)
Re: Fluctuating THINKING, Loping MEMORY, Erratic Surging STUPIDITY & Coughing Sign In

Yes - Mixed it up. The point is I think it was tested too soon guessing that it's now all set and that it just needs to run properly for a while and would be within spec after clearing out a bit. Seems it's been running poorly long enough AND is so close that the .23 PPM which is so little will just clear up soon on its own now. Not sure how each and every place tests as it changes here by the month it seems. No more tailpipe testing or "dyno" testing in MA if that was the way after too many accidents on machines.

Older vehicles meaning now pre OBDII just can't have anything visually wrong. Speaking for MA only and couldn't guess place to place what procedures are or have changed place by place, state by state. Now or not long ago the test was done on line connected to RMV (DMV same thing) still during the testing and the results were printed AND the sticker for windshield was printed on the spot actually by the "RMV" on the paper that both MAKES the sticker and hands you the results.

See note on this thread in tech's section guys.............

Tom







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