85 giving me fits!!! help needed
Thread Starter
Intermediate
Joined: Nov 2014
Posts: 25
Likes: 0
85 giving me fits!!! help needed
Hey all, I been using this forum a lot lately and finally its time I registered and asked.
Im currently working on my 85 vette and we've ran around this thing several times. Finally it is down to a rough low idle and sputters at the high rpm range. New fpr, new ecm, new injectors, fresh oil, new fuel filter, new maf, new air filter. Set timing to 6 deg. Ret., she smokes looks grey, low rough idle and plugs get black but I have fuel right at OE spec at least by my Chilton's which is 35 psi. Any suggestions would be good. The compression is lowish but consistent at 105 psi all the way around.
Thanks in advance.
Im currently working on my 85 vette and we've ran around this thing several times. Finally it is down to a rough low idle and sputters at the high rpm range. New fpr, new ecm, new injectors, fresh oil, new fuel filter, new maf, new air filter. Set timing to 6 deg. Ret., she smokes looks grey, low rough idle and plugs get black but I have fuel right at OE spec at least by my Chilton's which is 35 psi. Any suggestions would be good. The compression is lowish but consistent at 105 psi all the way around.
Thanks in advance.
Burning Brakes
Joined: Mar 2013
Posts: 1,131
Likes: 5
From: Illinois/Wisconsin Line
I'd say ur consistent lowish compression coming in at 105 across the board needs to be evaluated and might be the cause to several of ur systems. I'd be looking at ur timing marks and evaluating everything is coming up to TDC and is at TDC and looking at the valves for each cyl while its there
If sqirting oil into cyls will not increase ur compression. I'd say valve timing is off.
Also what kinda vacuum readings do you have at Idle and through out the rpm range
If sqirting oil into cyls will not increase ur compression. I'd say valve timing is off.
Also what kinda vacuum readings do you have at Idle and through out the rpm range
Last edited by cudamax; Nov 9, 2014 at 10:32 PM.
Thread Starter
Intermediate
Joined: Nov 2014
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I don't have a vacume tool to check but I did the old fashioned finger test and off the manufacture manual I recently bought what should sucks sucks and what should be pushing air pushes. I replaced the spark plugs adjusted the timing to 0 deg. She seems to respond a lot better. I'll try adding oil in the cyl. For a compression test tommorow see if that changes things. I wish I could get some history on the car to help troubleshooting but the actual owner walked in his front door and dropped dead. Rest his soul. So I've been testing and tracking everything from scratch.
Safety Car
Joined: Sep 2004
Posts: 3,953
Likes: 550
From: Mission Viejo CA
Question: What do you mean by "6 deg. Ret." Retarded? Are you saying 6 deg. after top dead center (ATDC)? If that's what you're saying, you should be at 6 deg. Before TDC (BTDC).
How many miles on the engine? Did you do the compression tests with the throttle blocked open? With only 105 compression pressure, you might want to start saving up for a rebuild.
How many miles on the engine? Did you do the compression tests with the throttle blocked open? With only 105 compression pressure, you might want to start saving up for a rebuild.
Thread Starter
Intermediate
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I may have misread but I thought it meant 6 degrees btdc, but it settle and smooths out at tdc exact. Engine has almost exactly 141,000. I was afraid someone might say that. Fortunately I have a good connection with a shop that will do the basic machine work for me. But I'll definatly start saving. With low compression will that screw with the idle?
Thread Starter
Intermediate
Joined: Nov 2014
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I just got it back from a run. Doesn't like high rpm at all but low and mid range rpm was average. But after 10 minutes of good running the lower parts of the exhaust manifold started glowing just a little.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
My evaluation is that your coolant temperature sensor on the front of the intake manifold is either bad or not connected properly (could be a corroded pin in the connector or broken wire). When that happens the ECM thinks the coolant temperature is -40° and it richens the mixture quite a bit, which causes the symptoms you describe.
Thread Starter
Intermediate
Joined: Nov 2014
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Well that's good to know. So I looked at it, its a little green around the exposed threads but nothing note worthy on the exterior of the sensor. Wires are all clean and insulated. So if its trying to compensate for presumed cold coolant that would take away top end power too?
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Race Director
Joined: Apr 2002
Posts: 10,036
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From: Anaheim CA
You can check the coolant temperature sensor with a digital voltmeter on the ohms range by unplugging the connector and probing the CTS pins. The resistance should correspond to the coolant temperature by this table:
Thread Starter
Intermediate
Joined: Nov 2014
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So I've heard this series of corvette is a basket case for wiring issues but after talking with one of my buddies. I've decided we are gona rip the heads off recut (hopefully) the burnt valves and rering the pistons. While we do that I will be afforded the opportunity to go through and inspect all plugs puns and connectors for corrosion as well as look at all the sensors. I'll get back to you guys after I've accomplished that.
Oil Producer
Joined: Apr 2014
Posts: 9,375
Likes: 2,737
if your exhaust manifold glows red?
is that not a sign of a plug cat? In which case could you be getting weird back pressure that screws are things? I am a newbie just tossing out ideas from what I read and I have learned on this forum. good luck I have an 85 as well.
Thread Starter
Intermediate
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It was a big factor until I cut the cat out and put a straight pipe in its place. I'm now debating the mufflers somehow being plugged a little too. But cutting the valves and fresh rings seems to be the best option for now.