86IROC112

I'm pretty sure the answer is no here but I'm running out of ideas. In my ongoing quest to fix my poor idle, I am running out of ideas and things to test.

The muffler on my car rotted and fell off prior to me buying it. I was wondering if the lack of back pressure could have any effect on my idle? I doubt it but like I said I'm running out of ideas...

Thanks

Bob88GTA

iTrader: (2)

Still chasing it?

Run on down to Midas and throw a cheap one on there.
But....ummm....no...not really. It'll sound better for one thing.

86IROC112

Yes, still chasing it. Keep finding little things I hope are the problem but it doesn't help. I think I'm going to send the injectors into South Bay and have them tested. Can't think of anything else at this point.

And yes, it sounds like a Mack truck using it's Jake brakes!

RedLeader289

iTrader: (2)

Checked all your vacuum lines?

86IROC112

Yes, I smoked the engine and my TB is a little suspect. Had smoke come from the butterfly shaft at the spring and from behind the TPS. I was told that may cause idle problems.

Ron U.S.M.C.

- Set timing,
- Reset IACV
- Set minimum idle speed.
In that order.

86IROC112

Hi Ron,


I've tried that several times. (Definition of crazy)


Is there a way to test the IAC itself? I found a thread on cleaning it but is there a way to test it? I saw very little or no difference when I tried to set it. Jump A&B, wait 30 seconds then start...Can't get it to idle under 750 without it stalling, then when I plug it back in, no difference..

aliceempire

iTrader: (14)

I should've asked this a long time ago...what is your timing set at? Did you disconnect the est wire when you set it?

86IROC112

Yep, disconnected the est and set it at 6BTDC. Have checked it a few times and watched as I rev the engine and it advances itself as it should. I am really almost positive I got the distributor in correctly. I Know I was at TDC when I installed it and not 180 off.??


This car is driving me nuts!

ex-x-fire

Make sure your egr valve isn't getting vacuum at idle.

86IROC112

Yep, tried unplugging and pinching off the vacuum line. No diff....

aliceempire

iTrader: (14)

three things come to mind..

Did you ever put a vacuum gauge on it? What does it show?

Did you see how it ran if you bumped the timing around a few degrees in each direction? Just to see if it seems any better anywhere else. The vacuum gauge will be useful here. What I'm getting at it the balancer could've spun.

And did you do a compression test? This motor is an unknown, you could chase you tail a long time going by what the seller told you it was.

-=Z28=-

iTrader: (3)

I agree with above, bump the timing around and see if you can get it to run better. Just cause it says to set it at whatever, doesnt mean that thats where your engine likes to run. Gotta listen to what your engine is telling you/trying to tell you.

86IROC112

I will try the timing. Where would I attach the vacuum gauge and what reading should I be getting? Also, the part of the MAS that attaches to the forked air cleaner assembly does not have the latch or whatever is suppose to connect the two. It has to be sucking a lot of air in through there. If that's in front of the MAS, would that make any difference?

Also, I talked to the machinist at NAPA and he remembers doing the engine work but I don't know if he's the one that assembled it or not?? I'll check the compression too..

I think I should also have my injectors tested? What do you think? They did sit outside in a plastic tub for upwards of a year even thought the PO says they are new..


I leave Sunday to go tear up the Oregon sand dunes for a week and will jump back under the hood when I get back... Can't wait to take her for her first drive in years...

aliceempire

iTrader: (14)

Vacuum gauges usually have a green area where vacuum 'should' sit when on a typical stock engine. I think it's normally between 17 and 20 in of vacuum. If you move the timing and it shows more vacuum or steady's the needle then start there.

You'll have to take a picture of the air cleaner duct work for me to be familiar. I think I have one laying around but I don't know what exactly yours is missing.

Nothing wrong with testing those injectors. Southbay is super helpful with all things injectors. Have fun in the sands.

novaderrik

to answer the question posed in the OP: no, you don't want "back pressure".. you never want it- it's always a bad thing. with a stock exhaust system, you've still got a bit of restriction from undersized pipes and the catalytic converter(s)..

86IROC112

So I met a guy in Oregon who has been a mechanic for over 30 years and seemed to know his stuff about these engines. He suggested I adjust my valves. So today I cleaned the IAC and adjusted the valves with the engine running. (Yuck, nasty job) Also played with the timing. NO CHANGE, still idles like garbage. Should
I take it out for a drive so the ECM learns the IAC position? Running out of ideas here...


I will try a compression check and vacuum check tomorrow.

Thirdgen89GTA

iTrader: (5)

God no, stock thirdgen v8's sound horrid without a muffler.

As for the poorly running issues? Its not the muffler. You need about 18" of exhaust behind the O2 sensor to keep the O2 in a steady stream of exhaust so it can read the Air/Fuel ratios.

86IROC112

I'm good there. The muffler fell of way at the rear of the car..

TylerSteez

iTrader: (3)

Your experience may differ from mine but when I smoked my motor I had a vacuum leak on my throttle body exactly where you described, I put a replacement throttle body on and my idle was perfect after.

CatmanFS

I had a 92 Z28 with a blown out cat that sounded fantastic. It was loud and throaty, and I could **** off all the hippie green air people whenever I hit the gas.

RubberDucky

iTrader: (4)

My Camaro has open headers, used to daily it that way.

86IROC112

Here's a picture of the vacuum gauge at idle. Rev the engine to about 1200-1500 and it goes into the green.


I played with the timing a little but will try again after the valve adjustment. About to check the compression. Any idea where it should be? I know I want them all about the same but don't know what a good reading is.


Also a pic of the connection point of the MAF to the air cleaner assembly..

Thirdgen89GTA

iTrader: (5)

I said Muffler, not cat converter. I don't have a cat on my car, nor a mid-pipe resonator (though I think I could add one). But I do have a muffler and will never run without. Especially not now that the car is cammed, headed, and running almost 11:1 compression.

Thirdgen89GTA

iTrader: (5)

What is the vacuum gauge at when at a stable idle?

Even my fairly aggressively cammed LT1 could still idle around 14".

aliceempire

iTrader: (14)

Was that vacuum gauge needle fairly steady while idling?


It's tough to call what compression should be, I'd be hoping for roughly 160 on a stock motor. It's relatively trivial, though you wouldn't want anything lower than 140ish across the board. Make sure you pull all plugs, open the TB, and disconnect fuel somehow so you don't flood the chambers.


I think there was a specific clamp made for that connection of the air cleaner. I may have a spare one...I'll check for you.

aliceempire

iTrader: (14)

That sounds terrible, I think you should move to LSx and sell that motor to....I don't know ...I guy about 90 minutes north of you.....

Thirdgen89GTA

iTrader: (5)

For the PITA that it was to get this engine built and running correctly you just MIGHT have scored such a deal.

I had to tear the heads off the car 3 times due to various issues with the ported stock castings.

I finally said F*** It and bought a set of AFR 195cc heads and haven't looked back. But then tuning it has been an experience as well.

You can find videos in the sig below.

aliceempire

iTrader: (14)

We're so way off topic now.
Ha, I already scouted your vids. I'll admit, I won't go so large of a cam but that doesn't stop me from enjoying others.
Weren't you running LE3's...you had problems with them ported out that far?

Thirdgen89GTA

iTrader: (5)

There were not ported by Lloyd, but that was as close as I could classify them. The port walls were too thin by the pushrods, and I started seeing pin-holes and ripples in the walls the longer they were on the car. I have them fixed now, but it was just easier to buy the AFRs and be done with it.

formula_novice

iTrader: (1)

So you have 11" of vacuum at idle? I haven't had a stock cam in a long time but that sounds really low. IIRC, stock on my 89 should be at least 15". I would replace the gaskets on the throttle body for sure.

If that doesn't fix it, take a volt meter and check the resistance (ohms) on each injector. Go ahead and check the fuel pressure at the rails too.

Hope this helps!

86IROC112

160 PSI??? If that's the case I have big trouble in little China here! Here were my readings:
#1 - 150
#2 - 95
#3 - 90
#4 - 80
#5 - 80
#6 - 70
#7 - 90
#8 - 95


The machinist told me sold the guy an "RV" cam which is not stock but very mild. How could I have 7 of 8 cylinders so bad? Can't all have bad rings.?


Here's a picture of the plugs. All 8 exactly the same. Black soot all over them. Not wet at all and it does not smoke.


Help guys...

86IROC112

I'm told the cam is not stock but only about one step up from stock, very mild. All the gaskets are new and I have checked the OHMs on the injectors and the fuel pressure. Looks like I have a compression problem..Look at my previous post.

formula_novice

iTrader: (1)

IIRC, the readings should all be roughly 140-160. What kind of shape are the heads in? Leaking valves can cause low compression as well.

86IROC112

The engine is supposed to freshly rebuilt. Problem is the guy never really got it running and it sat A LOT. When removing the carb intake to re-install the TPI intake I recall thinking it did not look very "fresh" in by the valves which prompted me to go find the machinist and verify he actually did the work the seller claimed. The machinist remembered the guy and doing the work so maybe it just sat too long and things got rusty in there?

aliceempire

iTrader: (14)

Possible all but one cylinder's valves adjusted wrong(too tight, valves stay open)...poorly built or poorly broke in engine causing the rings to never seat...gauge not seating correctly to give accurate measurements...valve events off time (cam, timing chain)...

formula_novice

iTrader: (1)

I agree with aliceempire. If it were mine, I would readjust the valves and see if those compression numbers come up.

86IROC112

I readjusted the valves yesterday and they were super tight. The guy never drove the car cuz he never got it running good enough to drive it so the rings may have not seated properly? Also make me wonder since the valves were so tight the ones left compressed could have gotten some rust on the mating surfaces. (I did see some rust in there when switching out the intakes) Going to try a leak down test per my new buddy in Oregon. He says pump about 100PSI into each cylinder and see if it leaks out the exhaust or intake valves. He also suggested I squirt a little oil into each cylinder then re-try the compression test. If compression goes way up, got a problem with the rings...


Good news I guess is that I think I finally found the problem. Would rather it be a sensor or something easy..

aliceempire

iTrader: (14)

Sounds like good news. Find a mild 350 and forget all about that abused 305.

86IROC112

I wish. Unfortunately it's my son's car and was to be a project for us to work on and we are on a budget. What would something like that cost and where would you find the engine?

Towelie420

my exhaust blew off and i drove it all screwed up like a madman for a really long time. i never had issues with backpressure when it was like that. it could be blocked or somthing

-vaccume system
-spark
-fuel
-compression
ive never been able to get mine to hold an idle in drive more than 500rpm but in neutral its solid 900rpm. i think its the auto trans clutches failing causing failure in drive but clean idle in neutral

aliceempire

iTrader: (14)

Purely on a budget I'd find a local L98. It may take some time but they're out there. See it in person and you could check casting numbers and possibly compression. All you'd need is a set of 22lb injectors and the correct PROM and you're on your way.

If I had a bit more buget my route would be to buy a GM crate. Like this vortec.. http://www.summitracing.com/parts/na...0282/overview/ Then you'd just need a vortec base (can be found pretty easily on the boards here) injectors and a corrected PROM. You would have a solid motor with a warranty AND room to grow when it's not fast enough any longer.

Or if I had more budget and time (that I don't have in real life) I'd find a LSx and fab up a turbo.........maybe drop in that LS7 you got there....

RedLeader289

iTrader: (2)

Depends on how much is in your budget but cheap 350's can be found at local swap meets, craigslist, or junkyards. If you really want to make it simple you can rip the efi out and throw a carb on it, but again, all depends on your budget.

TylerSteez

iTrader: (3)

My exhaust was completely cracked and broken off at the y pipe and I drove it for a while like that, actually just fixed it three days ago when I finally got my welder out of storage. It did run better but only because the crack was close enough to the o2 sensor to give it a false reading.