Rocket 350 Rough idle in gear, mystery continues

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Old November 4th, 2016 | 04:47 PM
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Rocket 350 Rough idle in gear, mystery continues

This morning I went up and bought a new coil after destroying my old one the night before, put it in and problem is still there.

Decided at this point after some tinkering around to replace my fuel filter between the tank and the pump to see if maybe it had caught something, or water in the gas had screwed it up, and noticed bit of an improvement after that, so I swapped the fuel filter between the pump and the carb and again an improvement but not totally gone.

It was at this point that I noticed the fuel flow through the filter was quite inconsistant, when the car is idling in park the filter stays full of gas but the input is inconsistant, and when it does go in it alternates between constant and sputtery, when I put the car in gear this worsens, to the point the filter can go completely dry and then fuel will sputter in and fill it part way and then go dry again, I could have sworn the car didn't do this before and the filters stayed with a constant level of fuel.

Edit: Forgot to mention, changed the PCV valve and oil filler cap to rule them out and make sure blowby isnt going up into the dizzy.

And sometimes when the car is warm and I start it without pumping the gas it will fire up but idle kinda low/slightly rough and itll either smooth out over time, or i can rev it once or twice and itll straighten out, dunno if this could be a fuel pressure thing or what.

Is it possible to have some sort of vacuum leak in the tranny? I noticed it was going into gear kinda hard this morning when it was cold but it might've been idling a little higher after I put the new coil in combined with the fast idle

Im thinking maybe the fuel pump is starting to go and when the RPMs are low the volume of flow is low enough to make it run rough, but at higher rpms its still putting out enough fuel? Or am I stupid? Or is it a carb issue or some kind?

Im starting to lose my mind and spent the whole night yesterday and today screwing with thsi thing when I should have been studying for my 1st year apprentince final, luckily I still got a good mark and should pass the course easily haha, if only this was worth marks, but now im basically out of cash until I start working again and would like to get this issue figured out because although the car is driveable I dont know what this problem is and would like to avoid getting stranded, its also frustrating because I had the car running flawlessly for the first time a couple weeks ago and then this starts.

Last edited by CyberCholo; November 4th, 2016 at 04:55 PM.
Old November 4th, 2016 | 05:21 PM
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Originally Posted by CyberCholo
... when the car is idling in park the filter stays full of gas but the input is inconsistant, and when it does go in it alternates between constant and sputtery, when I put the car in gear this worsens, to the point the filter can go completely dry and then fuel will sputter in and fill it part way and then go dry again...
This is normal.



Originally Posted by CyberCholo
... sometimes when the car is warm and I start it without pumping the gas it will fire up but idle kinda low/slightly rough and itll either smooth out over time, or i can rev it once or twice and itll straighten out...
This is normal, too.



Originally Posted by CyberCholo
Is it possible to have some sort of vacuum leak in the tranny?
Yes. You could have a hole in your vacuum modulator diaphragm, which will create a vacuum leak, causing rough running, and also make the transmission shift much too high, and your exhaust blow white smoke.

Easy way to check: Pull vacuum hose that goes to the modulator and see whether there is ATF inside. Plug the port you unplugged it from and see whether the idle smooths out.

- Eric
Old November 4th, 2016 | 05:28 PM
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The trans shifts great, and I do have a bit of the typical white vapour starting on a cold morning but it doesnt ever do it once the cars warmed up or been running for a bit, dunno if that counts.

I'll have to take a look tomorrow at it, thanks, its worth a shot.
Old November 4th, 2016 | 05:30 PM
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That's probably okay, then, but when you are concerned about a rough idle, it's always a good idea to disconnect vacuum accessories one at a time and see whether any of them causes an improvement.

- Eric
Old November 4th, 2016 | 05:50 PM
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Yeah I gave it a shot quickly and no improvement.

I tried unhooking vacuum advance earlier, and also my brake booster is disconnected and blocked off due to it leaking vacuum and not working and making my idle worse when stopped and its been not working so long that im used to manual brakes and every time Id have a bit of extra cash to do the booster something would come up haha.

Man this is frustrating, maybe the distributors toast? Didnt seem like there was much play in the shaft at all but I dont know what im looking for at the same time.

Maybe a plug wire thing? but theyre only a few months old and it seems like that would continue at higher rpms

Ive noticed sometimes when I let the car idle in park at higher rpms for awhile then put it in gear itll idle nicely for a bit and then gradually start to miss over about a minute or so, which is what made me think it might be connected to fuel
Old November 4th, 2016 | 06:05 PM
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This sounds like a problem that nobody could realistically help you with without being there and actually hearing it in person.

It could be a huge number of things, or it could actually be within normal limits.

I'd try to find out whether we have any members out there in BC who'd be interested in coming for a visit.

- Eric
Old November 4th, 2016 | 07:10 PM
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Im thinking its one of those things thats going to be something it shouldn't be haha.

I ran it by my teacher and hes of the opinion of a vacuum issue too, but vacuum is good and solid so im not sure. Wish I had some spare parts I could swap out to see if it makes any difference. My only guess was the transmission modulator but its not that.

I want to say maybe the fuel pump is going or is gummed up somehow, it looks like the original pump. I dunno, if it it was a carb issue it seems weird that it would only act in such a specific way, and if I pulled it off I Dunno what id be looking for, I Rebuilt it a few months ago so I doubt its carb related but who knows.



Maybe its time to set it on fire for the insurance money.
Old November 4th, 2016 | 07:26 PM
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You don't need 2 fuel filters, take the one out before the pump. Did you look down into the carb while the engine is running to see if there was fuel dribbling/spitting in there. If your idle was high it will jerk when you put it in gear. If your timing is not jumping around then your distributor is probably good.

Do you get the miss just at idle or is it there while cruising?
Old November 4th, 2016 | 11:48 PM
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Since you said you rebuilt the carb, are you certain you set the float level correctly?
Old November 5th, 2016 | 11:12 AM
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I looked down the carb a few times and everything looks fine.

The rough idle is only there below a certain rpm id say anything below about 1000 its hard to tell cause the tach starts jumping at the same time, the only time rpm is that low is idling usually though itll sometimes start to do it when im coming to a stop.

I checked the float level and it seemed good, the car doesnt stall when coming to a hard stop or anything. And I rebuilt the carb back around spring time I think and its been fine since then except for having to install a missing thermostatic coil and setting up the choke. I've also been running it with two filters, well its been like that since I bought it, and wasnt told I didnt need the second one until after I already had replaced both of them. I guess it could be the issue but seems weird it would do it all of a sudden.
Old November 5th, 2016 | 11:23 AM
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Originally Posted by CyberCholo
The rough idle is only there below a certain rpm id say anything below about 1000 its hard to tell cause the tach starts jumping at the same time...
Have you tried disconnecting the tach. to see whether it improved?

- Eric
Old November 5th, 2016 | 12:07 PM
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Not yet but ill give it a shot.

Is it possible the wire off hte positive coil is causing some sort of interference?
Old November 5th, 2016 | 12:37 PM
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On my ignition coil bracket theres a wire that comes off the negative terminal and goes into a little cylinder with a rubber boot at the top of the coil bracket, is there any way this has gone bad? I cant find any mention or replacement part for this thing anywhere online.
Old November 5th, 2016 | 12:40 PM
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Originally Posted by CyberCholo
Is it possible the wire off hte positive coil is causing some sort of interference?
It is possible that the tachometer could be grounding the ignition intermittently.



Originally Posted by CyberCholo
On my ignition coil bracket theres a wire that comes off the negative terminal and goes into a little cylinder with a rubber boot at the top of the coil bracket, is there any way this has gone bad?
That's a radio frequency suppressor. It helps prevent static on your radio (especially AM).

Don't worry about it.

- Eric
Old November 5th, 2016 | 12:41 PM
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That's a noise filter to reduce ignition noise from being coupled into the radio.
Old November 5th, 2016 | 03:07 PM
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Problem solved, one of the screws holding the points in had backed off a little bit and it could move around sligtly, tightened it back down and car runs perfect, tach works perfect needle is dead steady.

Wish I would have checked that earlier, but it forced me to tie up a few minor loose ends I had been putting off on the car, and apart from replacing the cheapo coil I broke with a decent standard motor products one and burning a bunch of gas from starting the car over and over it didn't cost me too much.

It being that screw backing off makes sense though, explains how it gradually got worse and worse and would come and go, and also explains why me taking the cap and rotor off would make it go away sometimes as I Imagine I would bump the points putting the cap on.

I also pulled that radio noise filter off for now, as my car currently has no radio as the AM radio in it broke, and it was interfering with my aftermarket air cleaner a little bit by being really close to it.
Old November 5th, 2016 | 03:09 PM
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There you go!

It's always something simple.

Glad you got it fixed!

- Eric
Old November 5th, 2016 | 03:32 PM
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Glad you found your issue.
Old November 5th, 2016 | 04:28 PM
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A side note here, I run 2 fuel filters on my 76 Olds. An inline before the pump and an inline after the pump.
I know it isn't really necessary, but I have caught small particles of the sock filter before the pump.
I'll need to replace the fuel sending unit in the tank soon I would think.
I put a fuel pressure gauge inline after the pump as well, it doesn't seem to get any fuel starvation with both filters.
The gauge is always around 4 to 4 1/2 psi. ( Moroso gauge)
Good to hear you got the problem sorted out.
Eric
Old November 5th, 2016 | 06:32 PM
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Good job...
Old November 6th, 2016 | 11:01 AM
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Originally Posted by 76olds
A side note here, I run 2 fuel filters on my 76 Olds. An inline before the pump and an inline after the pump.
I know it isn't really necessary, but I have caught small particles of the sock filter before the pump.
I'll need to replace the fuel sending unit in the tank soon I would think.
I put a fuel pressure gauge inline after the pump as well, it doesn't seem to get any fuel starvation with both filters.
The gauge is always around 4 to 4 1/2 psi. ( Moroso gauge)
Good to hear you got the problem sorted out.
Eric

Yes, I also forgot to add I took the filter out of the front of the carb cause I figured it was bit overkill. But yeah I'd rather have too many filters than not enough haha. I also try to keep my car over a half tank at all times.
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