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87 2.9L running rough - running out of Ideas!


MarkusMcBride

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Hi, My 87 2.9L manual ranger is running rough and I am running out of ideas as to what it could be. Here's what it runs like:

Idles a bit rough tho not bad enough to stall. All cylinders are firing just not at 100%. When reved up, it smooths out, quits shaking.

What I've done: I had the upper intake off and replaced the valve cover gaskets, i actually took 12 of the 16 valve cover bolts out by hand. I replaced the dist. cap and rotor, all wires, new coil, I did not change the 2 year old plugs as they still look in great condition. I threw it all back together and did notice improvement tho its not where i want it to be. I did a compression test and all cylinders were roughly 125-135. so no rings and no valves/heads.
When i took the fuel rail apart, I noticed that one injector wasn't stock and looked different. I believe it was above the pass. side rear cylinder which had the only plug that wasn't burning fully. the previous owners mechanic changed a few things to do with the fuel system, the lines look aftermarket, the filter looks newer and the fuel pressure reg. is brand new.

What do you guys think, where should I go next here and/or what are some tests i can do to try to isolate the problem? Help is appreciated! There are other issues with the truck but I am focussing on the running condition before anything else.
 


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Spott

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Are there any codes in the computer? Is there any chance of exhaust leaks between the engine and the cat? Have you tried running a couple tanks worth of fuel injector cleaner through it?
 

MarkusMcBride

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Havent been able to get the codes checked. Need to find someone with scanner. I Have run a full tank of shell 91 octane with injector cleaner. There is a leak between manifold and cat! on Pass side - what effect can that have? I never put much thought into the leak (at the flange from Mani pipe to Y pipe)
 

Spott

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That leak can draw fresh air into the exhaust pipe at times, which is then picked up by the oxygen sensor and the computer then changes your fuel/air ratios to something unbalanced, causing things to run poorly.

The codes on those old OBD1 computers can be read with a 12v test light, you just count the flashes. I'm sure there's instructions in the tech library.
 

black_demon69

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Hi, My 87 2.9L manual ranger is running rough and I am running out of ideas as to what it could be. Here's what it runs like:

Idles a bit rough tho not bad enough to stall. All cylinders are firing just not at 100%. When reved up, it smooths out, quits shaking.

What I've done: I had the upper intake off and replaced the valve cover gaskets, i actually took 12 of the 16 valve cover bolts out by hand. I replaced the dist. cap and rotor, all wires, new coil, I did not change the 2 year old plugs as they still look in great condition. I threw it all back together and did notice improvement tho its not where i want it to be. I did a compression test and all cylinders were roughly 125-135. so no rings and no valves/heads.
When i took the fuel rail apart, I noticed that one injector wasn't stock and looked different. I believe it was above the pass. side rear cylinder which had the only plug that wasn't burning fully. the previous owners mechanic changed a few things to do with the fuel system, the lines look aftermarket, the filter looks newer and the fuel pressure reg. is brand new.

What do you guys think, where should I go next here and/or what are some tests i can do to try to isolate the problem? Help is appreciated! There are other issues with the truck but I am focussing on the running condition before anything else.

did you check your firing order then check again? could have 2 cylinders in wrong place on the cap.. also look for moister and carbon tracking in the dist. cap...
 

enjr44

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On a fuel injected engine any exhaust leak before the last O2 sensor can/will cause a rough idle. The short term fuel trims will be messed up.
 

huh?

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how many miles do the 2 year old plugs have on them?
 

MarkusMcBride

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Awesome, that makes sense now - the leak is pretty big at that flange. Now I guess the call I have to make is do I buy new headers or try to patch the leaking flange.. The headers aren't shot right through, its just that damn flange!

Part two to that is do I try to take that job on myself if I have to replace the headers? I have time, that's not the issue, but I don't have a torch or impact..

What do you guys recommend? And if I do get new headers, what kind/where do you recommend buy?


Thanks a lot, the way the idle is rough and the way it slowly loses rmp on hills - it just didn't make sense after the tests I've done. I did a rubber glove test on the rad yesterday too. (remove rad cap, tape glove on, pinch off rad overflow hose, turn over engine - glove don't bounce = head gasket not leaking into cooling system)
 
Last edited:

MarkusMcBride

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Thanks Spott, I'm thinking you might be right here. You too enjr44. black_demon69 ya my firing order is correct, I just did the cap rotor and wires. The old cap had carbon tracking (corrossion) but I replaced it like I said.
Thanks everybody
 

MarkusMcBride

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Not to be a pain, but can someone please help me out with the questions I have above in the Bold section? Please and thanks, I do appreciate it.
 

MarkusMcBride

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That leak can draw fresh air into the exhaust pipe at times, which is then picked up by the oxygen sensor and the computer then changes your fuel/air ratios to something unbalanced, causing things to run poorly.

The codes on those old OBD1 computers can be read with a 12v test light, you just count the flashes. I'm sure there's instructions in the tech library.
Trying to figure out how to respond so that you get notified. Not trying to be a pain, but I could use a hand with the questions I had about solving the leak.
Thank you :beer:
 

Spott

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I didn't respond because I didn't feel I had a suitable answer. Since you insist, you get a lousy, ambiguous answer.

I have no way of knowing what sort of leak or crack you have in your manifold, thus no way to give a definite instruction. If it's just a crack in the cast iron, it can be V-grooved and TIG welded with nickel-99 or silicon bronze filler rod. If it's a big chunk rusted away or missing, you'll have to get a piece of "ductile iron" material and shape it to fit, before welding it in. You'll almost certainly have to take the manifold off to weld it.

I have no idea what headers or manifold to recommend, if you wish to replace it. The safest bet is a stock manifold, probably from a junkyard. Any of the 2.9l RBV model years will make a good donor. A manifold, even with rusted and/or broken bolts/studs, can be removed with hand tools if you're patient, do all the prep work you can, and know some tricks for solving problems. Too much Kroil is almost enough.

Nobody can give you a definite answer as to whether you should repair or replace, without seeing it themselves.
 

Andy D

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You won't know what you can do until you remove the headers.
 


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