Intermittent rough idle, hissing, a backfire threw intake

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Moparornocar0346

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Hello all. Ok so I have a 99 ram 1500 5.9 magnum and been having some issues trying to figure this out for sometime. It has a rough idle and loud hiss(cai sucking a lot of air) and just yesterday it backfired threw my intake. It’s never done that before. And there is no codes, so here is all of what’s new, upstream o2, Hughes plenum plate and gaskets, coolant temp, tps, crank sensor. Plugs, wires, cap and rotor. Imma bout throw my hands up foreal. It’s seems that it does it while it’s in park idling then I can put it into gear and it’ll straighten up after a few mins. Y’all have any ideas where I could start next?


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CupidStunt

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I'd say throttle body positioning sensor or clogged catalytic converter or you could need to clean out the throttle body. The fact that it takes time I'm leaning toward catalytic converter.
 
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Moparornocar0346

Moparornocar0346

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I'd say throttle body positioning sensor or clogged catalytic converter or you could need to clean out the throttle body. The fact that it takes time I'm leaning toward catalytic converter.

The cat is deleted and tps is new unfortunately.


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Dan98

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Probably has ignition issues like plug wires cap rotor crossfire maybe clean Tb and idle air control gets gummed up or stops working. But that's what the hissing sound is from IAC not operating properly. The backfire gotta be stray voltage between rotor and plugs like bad or burned plug wire. I have seen the cap get hot inside and start melting on to the rotor.
 
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Moparornocar0346

Moparornocar0346

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Probably has ignition issues like plug wires cap rotor crossfire maybe clean Tb and idle air control gets gummed up or stops working. But that's what the hissing sound is from IAC not operating properly. The backfire gotta be stray voltage between rotor and plugs like bad or burned plug wire. I have seen the cap get hot inside and start melting on to the rotor.

Well I don’t think I have the wires routed right I’m not sure. Imma have to look up that tsb again. Imma try a iac this evening and see what happens. If the dealer has one. I did clean the throttle bodie when this all started happening. Maybe the iac just doesn’t work like it should


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Okiespaniel

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There's a TSB for plug wire routing but your wires have to be on the right plugs first. Apparently listing the site upsets the forum god(s) so you'll have to google it. This TSB solves cross firing of ignition wires at the cap

Backfire through TB is a lean condition. If your IAC isn't working correctly and the throttle plates open before the IAC can respond it might induce a lean condition and backfire. The IAC plunger and it's mating service should cleaned with fine steel wool as well as the passage under the TB where the IAC bleeds through. This is the air part of the idle circuit.

Your Ram doesn't have a pickup coil. The item under the distributor rotor is the cam sensor. It seldom fails but a stretched timing chain can play with the fuel sync by giving wrong readings to the sensor. Haven't heard of it inducing backfire.
 
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Moparornocar0346

Moparornocar0346

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There's a TSB for plug wire routing but your wires have to be on the right plugs first. Apparently listing the site upsets the forum god(s) so you'll have to google it. This TSB solves cross firing of ignition wires at the cap

Backfire through TB is a lean condition. If your IAC isn't working correctly and the throttle plates open before the IAC can respond it might induce a lean condition and backfire. The IAC plunger and it's mating service should cleaned with fine steel wool as well as the passage under the TB where the IAC bleeds through. This is the air part of the idle circuit.

Your Ram doesn't have a pickup coil. The item under the distributor rotor is the cam sensor. It seldom fails but a stretched timing chain can play with the fuel sync by giving wrong readings to the sensor. Haven't heard of it inducing backfire.

O ok I see. Well I did clean the iac so maybe the sensor itself is going back. Is there anyways of testing those


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Okiespaniel

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Yes...

You'll have to find it online.

Somewhere...there's a "Merry Christmas" thread somewhere where some wonderful soul downloaded the entire 2000 Ram service manual into a pdf file that you can load into your computer or burn to disc. Again, posting that info here upsets the god(s) so it can't be shared.
 

Dan98

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18436572 clockwise rotation drivers side 1357 passenger side 2468 #1 terminal on the cap points at #2 cylinder bb787df410e0e89bf46e55631d1af1b8.jpg

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Ram 1970

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Rough idle/sound of sucking air/backfire can be all the symptoms of a large vacuum leak. Bad vacuum hose to the brake booster? Cracked throttle body? Bad gasket? Those are my guesses....
 
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Moparornocar0346

Moparornocar0346

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Rough idle/sound of sucking air/backfire can be all the symptoms of a large vacuum leak. Bad vacuum hose to the brake booster? Cracked throttle body? Bad gasket? Those are my guesses....

Checked all hoses and all r good. Also looked down my intake for oil even tho I have Hughes intake kit but nothing


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Ram 1970

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You could have jumped a tooth on your timing chain also. Not as common, but it happens sometimes.
 

MTBrian

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Have you figured out your truck? Mine is exhibiting the exact symptoms.
I posted last night in the General Section about this very thing.
Let me know what you found out I've replaced more things than I can count and remember I'm absolutely fed up.
 

ViolentMouse

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Okie is correct, backfire through intake is a "Lean" pop. only two ways the 5.9 does it. Either you are lean, or your are firing out of time via bad wires, wire routing, or mechanical timing failure.

First step, put a scantool on the vehicle and check the fuel sync and verify the ECU timing with a timing light and make sure they line up. that eliminates mechanical timing in minutes.

second step, using scantool check your short and long term fuel trims. numbers in the double digit positive mean that you are running lean and adding fuel to compensate. numbers in the double digit negative mean your running rich and pulling fuel. Often times we see issues where the o2 sensors are bad and reading a full rich or full lean condition..... you should be able to check your o2 sensors in the scan tool by watching the numbers move from rich to lean as the fuel system tries to correct itself (in closed loop when warm)

Loud hissing is usually the IAC valve being very open, but the 5.9 has a loud throttle body to begin with. one of the reasons I suggest not using a CAI, and sticking to the stock box, unless you are running forced induction your motor will never outflow the stock airbox, and the stock airbox got it's air from the cold side of the fender to begin with.

finallycheck your wires. inspect them for burns, cuts, traces of carbon lines where they might be leaking voltage to ground or to other wires. Check your spark plugs for wear, check your cap and rotor for carbon fouling and cross talk inside the cap.

If you can't find the issue using the above steps, and you have no check engine light on, I can only assume you have stock heads and you might have sunk a valve seat or or four.

sunk valve seats are hard to diagnose on the magnum as they rarely show up in a cylinder leakdown or a compression test, but tend to make themselves obvious around idle.

some guys use a piece of cardboard over the exhaust to test for it, if the exhaust always pushes the cardboard away from the pipe then valves should be fine.... if the cardboard gets blown away and then suddenly gets sucked up against the exhaust pipe, then usually indicates a sunk exhaust valve. which will cause a lean pop on mild to heavy acceleration because instead of getting the proper A/F mix that cylinder, its drawing hot air back in from the exhaust and causing a lean condition. This is tricky because it usually affects one cylinder at any time and has such a small effect on the fuel trims that it often goes without setting an engine light.
 

Dan98

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Yeah I had one suck back like that because the passenger side head warped then sucked the 4 and 6 fire rings in over the pistons. Run it at a high idle at night and see whare the exhaust manifold is glowing that be the sign.

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