89 Cuts out on idle - Corvette Forum : DigitalCorvettes.com Corvette Forums
 
 
Go Back   Corvette Forum : DigitalCorvettes.com Corvette Forums > C4 Corvette Forums > C4 Corvette
Register Forums Garage Garage Mark Forums Read Auto EscrowInsurance Advertise

Notices

C4 Corvette General | Technical | Performance | Aftermarket | Discussions

Other sections:
Corvettes Classifieds
Corvette Detailing & Car Care
Corvette Audio/Video/Radar
General Automotive/Shop/Tools
Corvette Performance Driving/Racing

Shops/Tuners
Custom Image Corvettes
A&A Corvette
Corvette tuner

Interior
Corvette aftermarket products

Insurance



Parts & Products
Race Ramps
Edelbrock
ATI/Procharger
Corvetteguys.com
Melrose Motorsports
Parts Taxi
Airaid
Pfadt Racing
Madvette Motorsports
Hi-tech Custom Concepts
Corvette Garage
Corvette Parts and Accessories
Corvette Car Care Products
Corvette HID

Tracks/Schools
Bob Bondurant School of High Performance Driving
Corvette driving school

Wheels/Tires
Cray Wheels

Services
BADWERKS.com
Reply
 
Thread Tools
Old 02-16-2019, 04:34 PM   #1
Zacks89
DC Crew
 
Posts: 5
Member #181072
Member since: Feb 2019

Thanks: 0
Thanked 0 Times in 0 Posts
89 Cuts out on idle

Hi I have an issue with my car where when I accelerate it cuts out and then the RPMs go up after about a second. I have replaced many parts including the mass air flow sensor and fuel pump idle air control throttle position sensor. I had to head gaskets recently changed and I truly believe that I have no vacuum leaks. I used to have an 85 Corvette that had a similar problem but I can't remember what I did to solve it. if anyone will be
able to help me out it'll be greatly appreciated I've dumped a lot of money and time into this car and everything I keep trying is not working. I put a video on YouTube . In the video that's a fuel pressure gauge connected to the straighter valve. I want to also add that when I set the minimum idle it ran perfectly smooth at 400 RPM. thank you.https://youtu.be/kWa7tQ3RNBA
Zacks89 is offline   Reply w/quote Quick reply to this message
Sponsored Links
Advertisement
 
Old 02-16-2019, 07:41 PM   #2
autowiz
DC Crew
 
autowiz's Avatar
 
Posts: 4,685
Member #149514
Member since: Nov 2014
Location: Pompano Beach, Fl USA

My Corvette(s)
2000 silver/black

Thanks: 307
Thanked 364 Times in 319 Posts
These early control systems were problematic. You will finally track down this problem to soon have another. There is a wounderous solution to these problems for GM's tuned port motors in F.A.S.T.'s easy efi multi port retro fit. This kit:
https://www.fuelairspark.com/ez-efi-...-fit-type.html

FAST is an excellent control system. And reliable. This will replace your engine harness and ecu only with a fully self tuning and extremely reliable solution. It comes with a touchscreen that mounts to the windshield.
autowiz is offline   Reply w/quote Quick reply to this message
Old 02-16-2019, 07:51 PM   #3
1963SS
DC Crew
 
1963SS's Avatar
 
Posts: 4,668
Member #96709
Member since: Dec 2009
Location: Eastern, KY

My Corvette(s)
1995 C4

Thanks: 230
Thanked 873 Times in 524 Posts
It appears from the video that you've got a fuel pressure issue. Check the fuel pressure at the schrader (straighter) valve at idle and then check it again with the vacuum hose to the fuel pressure regulator unplugged. It seems that the fuel pressure drops as you rev the engine.
1963SS is offline   Reply w/quote Quick reply to this message
If smoking marijuana causes short term memory loss

What does smoking marijuana do?
 
Old 02-16-2019, 08:25 PM   #4
Zacks89
DC Crew
 
Posts: 5
Member #181072
Member since: Feb 2019

Thanks: 0
Thanked 0 Times in 0 Posts
If the vacuum hose disconnected the fuel pressure stays at a steady 45 PSI. But the hesitation stillis there. I've even tried partially clamping off the fuel return line.
Zacks89 is offline   Reply w/quote Quick reply to this message
Old 02-17-2019, 11:06 AM   #5
autowiz
DC Crew
 
autowiz's Avatar
 
Posts: 4,685
Member #149514
Member since: Nov 2014
Location: Pompano Beach, Fl USA

My Corvette(s)
2000 silver/black

Thanks: 307
Thanked 364 Times in 319 Posts
Quote:
Originally Posted by Zacks89 View Post
If the vacuum hose disconnected the fuel pressure stays at a steady 45 PSI. But the hesitation stillis there. I've even tried partially clamping off the fuel return line.
forcing the pump to fight dead head pressure is only going to complicate whatever problem you are already having. The C4 was GM's time to figure out electronic fuel injection. You should be happy you do not have their first attempt, the cross-fire fuel system that was used for just 2 years. the last of the c3 and the first of your c4. Then in 1985 the first year of your tuned port was a whole mess too. This was because there was a separate module just to interpret the mass air flow sensor and send the signal to the pcm. This maf module is out of production and even if it could be found they had an extremely high failure rate utterly killing the 1985 corvette unless you convert to a carb or aftermarket fuel injection

The maf module was so problematic that gm dumped the mass air flow sensor completely and went to Speed Density fueling with a map sensor only for a handful of years and then in the early 90's came back with both mass air flow sensor and manifold absolute pressure sensor and the ecu is constantly comparing the 2 for accuracy and diagnostics. This is the point where electronic fuel injection became stable for GM. and it happened right around the time of the LT motor being put in the C4.

There were some other strange things that were done by GM in these years as they struggled to figure things out. One problem was GM was caring too much about oil temp. And they drove the cooling fans based off of their firm belief in letting the oil achieve a temp that would allow the moisture to steam up and leave the crankcase. And so most C4's from the 80's and even into the early 90's in proper stock form will not even turn the coolant fan on until 238f is achieved in the coolant.

Also GM thought that linking fuel pump power to the engine's oil pressure was a great safety feature. Their thinking was if the oil pressure went away, the fuel would shut off saving the engine from imminent failure. What this looks like is a fuel pump relay driven by the PCM that lights the fuel pump when you turn on the key for a 2 second prime, and then an oil pressure switch that when closed sends power directly to the fuel pump. This has been the culprit of countless gremlins on these cars. This creates extremely long cranking times intermittent issues and even stalling on worn motors that drop oil pressure too low at idle.

And then we come to wiring. GM had to put so much copper in each of these Corvettes. At their peak in 1993 the Chevrolet Corvette had right around 200lbs of copper in each car and if you took all the wire out and stretched it end to end you would have over 2 miles of wire. That is a lot of 30+ year old connections to break down from fretting / micro motion. This problem drove GM to create and invent GMLAN. A novel way to drastically reduce the amount of wires and connections in each vehicle by letting modules communicate on 2 networks. A 1 wire low speed network for unimportant stuff and accessories and a 2 wire high speed network for all the important stuff like communications between the engine controller, abs unit, airbags, stuff that needs big information and fast. And for diagnostics here the stuff that talks on high speed usually also communicates on low speed.

There is a very good reason the aftermarket fuel injection companies have put together specific retrofit kits for these early GM fuel systems. They help. And from the time it goes in you don't fight with it anymore.
autowiz is offline   Reply w/quote Quick reply to this message
Old 02-17-2019, 12:01 PM   #6
autowiz
DC Crew
 
autowiz's Avatar
 
Posts: 4,685
Member #149514
Member since: Nov 2014
Location: Pompano Beach, Fl USA

My Corvette(s)
2000 silver/black

Thanks: 307
Thanked 364 Times in 319 Posts
There is also another thing here I would like to point out about these early control systems. The cross fire in '82 & '84 had 2 fuel injectors. So it's controller had 2 injector drivers. One fuel injector fired each bank. These were low impedence(peak and hold) fuel injectors we do not use today. Their drivers in the pcm had to be robust for their operation. When your tuned port came out GM added 8 fuel injectors as you see but made no changes to the controller. They used these 2 robust drivers to drive 4 injectors each simultaneously. Thus achieving bank fueling. This allows fuel/air mix to collect at the head of the closed intake valve and begin to separate from the atomized mix.


Sequential fuel injection is where we have a crankshaft position sensor and a camshaft position sensor and we have 8 fuel injector drivers and we time the opening of each fuel injector to the opening of that cylinder's intake valve. There are nothing but upsides to sequential fueling. From power production to efficiency to emissions to cleanliness of the intake and valves. So great and profound was sequential fueling when it came on the scene that it what everything made today is.


FAST makes a 'dual sync' distributor that provides both a cam and a crank signal back to the fast controller. This dual sync distributor with the multiport retrofit would allow you to achieve modern day fueling with your older Tuned Port fuel system. Here is that distributor: https://www.fuelairspark.com/chevy-s...stributor.html
autowiz is offline   Reply w/quote Quick reply to this message
Old 02-17-2019, 12:19 PM   #7
autowiz
DC Crew
 
autowiz's Avatar
 
Posts: 4,685
Member #149514
Member since: Nov 2014
Location: Pompano Beach, Fl USA

My Corvette(s)
2000 silver/black

Thanks: 307
Thanked 364 Times in 319 Posts
IF you were not interested in the more cost effective route of the multi port retrofit and wanted the fuel system that were gonna make the most power that you would feel driving then you should consider dumping the tuned port all together. Just unbolt everything toss it all even the lower intake. And rebuild with an edlebrock intake for a carb. Whichever you like. If you got a cam and are good past 6k rpm then get the victor jr. single plane, or get the performer RPM if you have the stock cam and valvetrain. And then get the FAST easy efi 2.0 kit with their carb replacing throttle body. This throttle body flows an industry leading 1150cfm. It has 8 fuel injectors built into it and claims 1200hp support all on it's own. The runners and throttle body on your tuned port will never flow these numbers no matter what you do. So if you were not looking to just solve your problems but wanted to make yourself some of that Lemonade we all love so much you might consider an Edlebrock intake and a FAST 30400-kit: https://www.fuelairspark.com/ez-efi-...-base-kit.html

I have set this up on a few C3's here:
https://www.digitalcorvettes.com/for...d.php?t=242889
Here:
https://www.digitalcorvettes.com/for...d.php?t=255809
And here:
https://www.digitalcorvettes.com/for...d.php?t=292602

The setup with their throttle body always impresses. Every single time. And all of their stuff is labeled and engraved made in the USA.
autowiz is offline   Reply w/quote Quick reply to this message
Old 02-17-2019, 12:43 PM   #8
1963SS
DC Crew
 
1963SS's Avatar
 
Posts: 4,668
Member #96709
Member since: Dec 2009
Location: Eastern, KY

My Corvette(s)
1995 C4

Thanks: 230
Thanked 873 Times in 524 Posts
Quote:
Their thinking was if the oil pressure went away, the fuel would shut off saving the engine from imminent failure.
I used to think that also but the oil pressure switch is wired parallel with the fuel pump. I believe it's a backup if the fuel pump relay were to fail. The fuel pump signal from the ECM energizes the relay and that supplies power to the pump. This is true on the LT1 Vettes, not real sure about an '89.

Quote:
Sequential fuel injection is where we have a crankshaft position sensor and a camshaft position sensor
......or the evil Optispark.

Quote:
most C4's from the 80's and even into the early 90's in proper stock form will not even turn the coolant fan on until 238f is achieved in the coolant.
Just a technical note.....the first fan comes on at 226 and will turn back off at 219. The second fan will come on at 235 or so and turn back off at 226......give or take.
1963SS is offline   Reply w/quote Quick reply to this message
If smoking marijuana causes short term memory loss

What does smoking marijuana do?
Old 02-17-2019, 12:52 PM   #9
autowiz
DC Crew
 
autowiz's Avatar
 
Posts: 4,685
Member #149514
Member since: Nov 2014
Location: Pompano Beach, Fl USA

My Corvette(s)
2000 silver/black

Thanks: 307
Thanked 364 Times in 319 Posts
Quote:
Originally Posted by 1963SS View Post
I used to think that also but the oil pressure switch is wired parallel with the fuel pump. I believe it's a backup if the fuel pump relay were to fail. The fuel pump signal from the ECM energizes the relay and that supplies power to the pump. This is true on the LT1 Vettes, not real sure about an '89.

It is wired in parallel because the ecu only supplies power to the relay for the 2 second prime. When the car is running the relay is not energized and power for the pump comes from the oil pressure switch. There is even a bad part that came with the cars and a TSB on replacing them if they are a certain color plastic. I will look for this bulliten and post here.

Later years and your LT switched away from this and the relay stays energized while the car runs. This is because GM learned that powering the fuel pump from the oil pressure switch was a bad idea. Very bad. But there is nothing that can be done with an ECU that will only energize a relay for prime. The LT ecu's can not be used here because they require low and high res pulses from the optispark. These early fuel systems sere just problematic. And the entire generation of a car has suffered a certain rep for unreliability as a direct result.


Even the opti was in and of itself a disaster. And All optispark was not sequential. The LT1 was the same bank firing as the tuned port. Only the LT4 with the red intake at the very end of the sbc's life had just touched sequential fueling. So many seals and a water pump within inches of an optical sensor. How can reliability ever be had out of that? And that was when GM finally got the right answer. CKP position sensor and a CMP position sensor. No distributor. Sequential fueling precise ignition timing without concerns about max timing adjustments allowed before jumping to adjacent towers.
autowiz is offline   Reply w/quote Quick reply to this message
Old 02-17-2019, 01:07 PM   #10
1963SS
DC Crew
 
1963SS's Avatar
 
Posts: 4,668
Member #96709
Member since: Dec 2009
Location: Eastern, KY

My Corvette(s)
1995 C4

Thanks: 230
Thanked 873 Times in 524 Posts
I'm probably just getting old but I thought the FP relay was energized for 2 seconds and then again when it sees reference pulses from the distributor either cranking or running. What if the 2 second prime is used up because the car had to crank for 5 seconds. That may not be enough time for the oil pressure relay to close and the car would never start. Logically, that doesn't make a lot of sense. You'd have to keep turning the key off and on after 3-4 seconds. Kinda illogical to an old Hillbilly.
1963SS is offline   Reply w/quote Quick reply to this message
If smoking marijuana causes short term memory loss

What does smoking marijuana do?
Old 02-17-2019, 01:11 PM   #11
autowiz
DC Crew
 
autowiz's Avatar
 
Posts: 4,685
Member #149514
Member since: Nov 2014
Location: Pompano Beach, Fl USA

My Corvette(s)
2000 silver/black

Thanks: 307
Thanked 364 Times in 319 Posts
Quote:
Originally Posted by 1963SS View Post
I'm probably just getting old but I thought the FP relay was energized for 2 seconds and then again when it sees reference pulses from the distributor either cranking or running. What if the 2 second prime is used up because the car had to crank for 5 seconds. That may not be enough time for the oil pressure relay to close and the car would never start. Logically, that doesn't make a lot of sense. You'd have to keep turning the key off and on after 3-4 seconds. Kinda illogical to an old Hillbilly.
I know, right? Well we didn't start off with the knowledge. And GM's Tuned Port was an early fuel system from a time before GM understood that the relay should always be energized. The pump gets its prime and then the car cranks until oil pressure closes the switch. This made for start n stall and long crank time conditions as the cars packed on the age and wear. And this made GM quickly move to having their ecu's just keep the relay energized. And there have been no problems since. But he has an early fuel system.


This has also brought about the solution to long cranking times as cycling the key twice before cranking to make the car start right up. How many early C4 owners know this trick?
autowiz is offline   Reply w/quote Quick reply to this message
Old 02-17-2019, 01:15 PM   #12
1963SS
DC Crew
 
1963SS's Avatar
 
Posts: 4,668
Member #96709
Member since: Dec 2009
Location: Eastern, KY

My Corvette(s)
1995 C4

Thanks: 230
Thanked 873 Times in 524 Posts
Quote:
The LT1 was the same bank firing as the tuned port. Only the LT4 with the red intake at the very end of the sbc's life had just touched sequential fueling.
I have LT1's and LT4's. Both are sequential. I believe the earlier LT1's were batch fire but the later 94-95-96 were sequential. Of course the LT4's being a 96 were batch fired. There was also sequential fuel injection used in 1990 on the beautiful LT5. The technology was there.
1963SS is offline   Reply w/quote Quick reply to this message
If smoking marijuana causes short term memory loss

What does smoking marijuana do?
Old 02-17-2019, 02:14 PM   #13
autowiz
DC Crew
 
autowiz's Avatar
 
Posts: 4,685
Member #149514
Member since: Nov 2014
Location: Pompano Beach, Fl USA

My Corvette(s)
2000 silver/black

Thanks: 307
Thanked 364 Times in 319 Posts
Quote:
Originally Posted by 1963SS View Post
I have LT1's and LT4's. Both are sequential. I believe the earlier LT1's were batch fire but the later 94-95-96 were sequential. Of course the LT4's being a 96 were batch fired. There was also sequential fuel injection used in 1990 on the beautiful LT5. The technology was there.
My bad. You are right 94, 95, 96 were all sequential. Well 1993 could have came both ways then. I vividly remember the 8th digit entry of the vin as selecting between sequential or port fueling for one of them. But that still doesn't make it a good fuel system, lol. Optispark as a whole represented GM's shift from reading engine positioning off of the camshaft to reading engine positioning off the crankshaft. And that was a bad idea. Because it is easy to know where the crank is when you read off the cam. 2x the number of desired teeth on the wheel and you are there. But it is impossible to know what stroke the engine is on when you are only reading the crankshaft. You can play with which stroke you fire the ignition system on during cranking to get a logical detection that you can struggle to remember the whole time the car is running. Ya know, or you can fire the coil every time the piston comes up. waste spark style. On compression and on exhaust. And the exact same applies with the fuel injectors. You can time their opening to that cylinder's tdc but you gotta fire it on both the intake and the combustion strokes. So really if we wanna be technical about it all it is more of a semi sequential than it is sequential fueling as we understand it today.
autowiz is offline   Reply w/quote Quick reply to this message
Old 02-17-2019, 03:01 PM   #14
1963SS
DC Crew
 
1963SS's Avatar
 
Posts: 4,668
Member #96709
Member since: Dec 2009
Location: Eastern, KY

My Corvette(s)
1995 C4

Thanks: 230
Thanked 873 Times in 524 Posts
Quote:
On compression and on exhaust. And the exact same applies with the fuel injectors. You can time their opening to that cylinder's tdc but you gotta fire it on both the intake and the combustion strokes. So really if we wanna be technical about it all it is more of a semi sequential than it is sequential fueling as we understand it today.
Not quite The Opti knows where #1 is. It's a pretty ingenious thing with different sized slots working in conjunction with the 720 (leading and trailing edge) pulses per revolution. According to my experience and my trusty noid lights I believe this to be true. Since I'm really old didn't your Momma tell you to respect your elders? I'm a retired Electrical Engineer and I'd be glad to break it down for you.......transistor by transistor.

If I drive to Florida I'll give Optispark lessons in exchange for a dyno tune discount. My tune currently is wideband based. It seems to work well. But I'd bet a dyno would be better, especially if YOU did it.

Oh, BTW, some of us only use the Opti for the pulses. Get the ozone away from the optical sensor and they might work forever. Over 200K on one Impala, 65K on the 6-speed and 150K on the Vette. All original optis.


Last edited by 1963SS; 02-17-2019 at 03:53 PM.
1963SS is offline   Reply w/quote Quick reply to this message
If smoking marijuana causes short term memory loss

What does smoking marijuana do?
Old 02-17-2019, 06:19 PM   #15
autowiz
DC Crew
 
autowiz's Avatar
 
Posts: 4,685
Member #149514
Member since: Nov 2014
Location: Pompano Beach, Fl USA

My Corvette(s)
2000 silver/black

Thanks: 307
Thanked 364 Times in 319 Posts
Those coils look good on that motor. And I respect the hell out of you, both of your impalas, and all of your thoughts and input.
autowiz is offline   Reply w/quote Quick reply to this message
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Corvette Forum : DigitalCorvettes.com Corvette Forums forums, you must first register.
Please enter your desired user name (12 CHARACTERS MAXIMUM), your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
City / State / Country?
Where you live
What kind of Corvette(s) do you own?
This field is not required.
Insurance
Please select your insurance company (Optional)

Log-in


Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Erratic idle / idle miss markk C3 Corvette 6 04-18-2011 09:32 PM
'Miss' at idle and just off idle - cause olddog C6 Corvette 3 09-18-2010 06:33 PM
DTC 48 (Mass Air flow Sensor Circuit) Slight rough idle, car cuts out. HELP! acedraven C4 Corvette 5 02-15-2010 12:02 PM
78 C3 high idle rough idle where to begin? markk C3 Corvette 2 08-28-2008 10:14 PM
'89 L98/ZF6 idle problem jpshark C4 Corvette 4 05-23-2004 12:40 AM

Powered by vBadvanced CMPS v3.2.2

All times are GMT -6. The time now is 02:27 AM.




Powered by vBulletin® Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Garage Plus vBulletin Plugins by Drive Thru Online, Inc.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
2003-2011, DigitalCorvettes.com - All Rights Reserved