C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

88 corvette HELP!!!

 
Old 03-03-2019, 06:06 PM
  #21  
gpierce
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Originally Posted by cdm747 View Post
gpierce I totally disagree with you. Look at the circuit. On the power to the fuel pump relay from the ECM it states Fuel Pump Control during start only. The circuit to the fuel pump is fed through the Oil Pressure Switch during normal operation. Please look at the wiring diagram I uploaded.
And I totally disagree with you. The circuit on the ECM is an integrated circuit, with program instruction. I know for a fact that program says to activate that circuit when pulses from the ICM are received. I believe you are misinterpreting the diagram to indicate that this is the ONLY time that circuit is activated, when it is not.
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Old 03-03-2019, 06:10 PM
  #22  
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Originally Posted by Tom400CFI View Post
IDK WHERE in the world you came up with verbage that says the ECM only commands the pump to run during cold start only. Leesvet?
In the FSM diagram it has words on that ICM connector that reads "During Start Only" and I think that generally this leads to the interpretation that in run and crank are the only times it is active. I know through specific testing that this is not the case. Perhaps it is in fact one of many mistakes made by GM when writing some of their FSMs.
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Old 03-03-2019, 06:11 PM
  #23  
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But, some people will never believe how it works

PS, those words are on the electrical diagram 8A-20-6

Last edited by gpierce; 03-03-2019 at 06:15 PM.
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Old 03-03-2019, 08:47 PM
  #24  
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I did post a diagram. It was a PDF attachment and the verbiage is on the diagram. Page 8A-20-6. I guess one day I will unplug the oil pressure switch to check for myself. Until then I can only go by what the schematic is showing.. This has been debated on more than one thread in the short time time i have been on the forum. Does anyone know exact;y what the ECM is doing or are you just doing an educated guess. The FSM leaves a lot to interpretation of what the ECM is actually doing
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Old 03-03-2019, 09:33 PM
  #25  
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Originally Posted by cdm747 View Post
Does anyone know exact;y what the ECM is doing or are you just doing an educated guess. The FSM leaves a lot to interpretation of what the ECM is actually doing
I "know" from both my own experience and from tests others have already done. Here's a good one!

http://www.misterpeachy.com/VetteStu...elay_Myth.html
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Old 03-04-2019, 07:54 AM
  #26  
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Well here is another good one. It appears to me from reading these two articles that if you don't have oil pressure the engine will not run unless the ECM is seeing at least 4 PSI from the oil pressure sensor. I am not trying to argue with you or Tom or anyone else. I was reading the schematic and that was my interpretation. Perhaps the article below will help Eddie77 solve has problem.

https://www.corvettebuyers.com/c4vettes/l98.htm

http://garage.grumpysperformance.com...-sequence.330/
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Old 03-04-2019, 09:58 AM
  #27  
Tom400CFI
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Originally Posted by cdm747 View Post
I did post a diagram. It was a PDF attachment and the verbiage is on the diagram. Page 8A-20-6. I guess one day I will unplug the oil pressure switch to check for myself. Until then I can only go by what the schematic is showing.. This has been debated on more than one thread in the short time time i have been on the forum. Does anyone know exact;y what the ECM is doing or are you just doing an educated guess. The FSM leaves a lot to interpretation of what the ECM is actually doing
I know what the ECM is doing. So does gpierce. Go unplug your oil pressure switch and see what happens. You have an opportunity here, to learn a thing. Take it.
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Old 03-04-2019, 10:01 AM
  #28  
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Originally Posted by cdm747 View Post
Well here is another good one. It appears to me from reading these two articles that if you don't have oil pressure the engine will not run unless the ECM is seeing at least 4 PSI from the oil pressure sensor. I am not trying to argue with you or Tom or anyone else. I was reading the schematic and that was my interpretation. Perhaps the article below will help Eddie77 solve has problem.

https://www.corvettebuyers.com/c4vettes/l98.htm

http://garage.grumpysperformance.com...-sequence.330/
The ECM doesn't "see" oil pressure. ECM has no idea, what the oil pressure is. The link above is totally wrong, and much of the terminology in it is way off too. It's was written by an amateur. You can believe that source...or your can find fact. Seek fact.
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Old 03-05-2019, 04:59 PM
  #29  
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Electrical oil switch or sensor will not fix engines low oil pressure. Low oil pressure will require mechanical engine repair. You need someone who knows more than you to help you. There's normally a "handy Andy" in every neighborhood. You will need mechanical oil pressure gauge, a fuel pressure gauge, and a spark tester. some auto parts stores will have them on loaner programs. You need to check fuel pressure (over 42psi) and for spark at 2 plug wires.
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Old 03-06-2019, 10:38 PM
  #30  
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This thread is quite comical. At this point, I don't think I would encourage Eddie to fix this car. Oh, ahhh, Tom and gpierce you could be wrong. Maybe the oil change was completed with the wrong viscosity of oil, and now the fuse is blown to the hi tech electric oil - sump - pump. Could be that simple. ------------ Tom and gpierce are 100 percent correct, and I am glad you both tried to help. Kevova you are correct as well.
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Old 03-06-2019, 10:56 PM
  #31  
Eddie77
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I want online and look up why my car is doing what it's doing I found a list of these items that says could be causing the problem I'm going down the list and I'm fixing all these problems but my car still doing it..
To go back to the beginning of my initial problem:
My car was stalling out once in a while until I would reset the computer by taking off the positive battery then put it back on.. I went online and it said it could be the ICM unit so I had one put on at the garage and I had my oil changed now my car won't run at all....
Here's a list of the things I'm replacing to try to fix my problem
  • Faulty fuel pump
  • Restricted fuel filter
  • Faulty fuel-pressure regulator
  • Leaking fuel injectors
  • Faulty oil-pressure sending unit
  • Faulty pickup coil (located inside the distributor)
  • Throttle-position-sensor (TPS) voltage too high
  • Faulty mass-airflow sensor (MAF)
  • Faulty coolant-temperature Sensor
  • Faulty engine controller
  • Pulsar on fuel pump
  • Distributor coil
  • If anyone has any thoughts of what else it might be I'd appreciate your input but basically all the information I've got so far is really done me no good....thanks
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Old 03-06-2019, 10:59 PM
  #32  
Eddie77
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Also as a side note please do not send me all these pictures of diagrams and wiring units and all this other crap because I am not a car guy I do not understand it I would like to know is a plain and simple answer of what you feel I might need to change on my car to solve my problem....
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Old 03-07-2019, 06:34 AM
  #33  
Joe K
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Originally Posted by Eddie77 View Post
Also as a side note please do not send me all these pictures of diagrams and wiring units and all this other crap because I am not a car guy I do not understand it I would like to know is a plain and simple answer of what you feel I might need to change on my car to solve my problem....
Ok I will tell you exactly what you need to change. The person who is working on it. Find and take it to a shop that knows Corvettes. You asked.
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Old 03-07-2019, 12:08 PM
  #34  
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Originally Posted by Eddie77 View Post
the ICM unit so I had one put on at the garage and I had my oil changed now my car won't run at all....
This should be super easy then. When it won't start, what's missing: Spark or fuel? Easy.
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Old 03-07-2019, 12:28 PM
  #35  
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If a car won't start, its fuel or spark. You need to start working on the car and eliminate problems. If you can't look at the diagram and figure out what to do, then go buy a Helm manual and take that to your mechanic and tell him to fix it.

Hook up a fuel pressure gauge at the rail. Turn key to RUN but do not start, tell us what the pressure is and whether it holds steady. If the pressure never comes up, then its the pump circuit that you need to work through.
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Old 03-08-2019, 09:50 AM
  #36  
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If the car won't start, start by hooking up one end of a wire to a 12 volt power source. The battery would work. Touch the other end of the same wire to terminal "G" in the ALDL connector. If you hear the fuel pump running then it works, if not then it's a wiring/relay problem or the pump itself.

As for the bad idle, check your vacuum lines. Good chance your EGR valve isn't getting enough vacuum. This is likely your issue.

Oil pressure switch should be for the light, the oil pressure sensor is for your gauge. It's very common for the gauges and switches on these cars to fail due to age and sludge build up. If you don't have oil pressure on start up the lifters won't get oil you'll be easily able to hear the valve noise right away. If that's the case have a mechanic look into it.

Last edited by VETTLIFE; 03-08-2019 at 09:56 AM.
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Old 03-10-2019, 04:27 PM
  #37  
Eddie77
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Thank you everyone for your help.....i have 1 more question....is the fuel pressure relay the same as the mass air flow relay....
Meaning are both the relays the same..i.e..i installed a mass air flow relay where the fuel pressure relay spot....i read they were the same unit...
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Old 03-10-2019, 04:57 PM
  #38  
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MAF relay, MAF burn-off relay and FP relay are all separate. Three different relays.
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Old 03-10-2019, 05:01 PM
  #39  
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Yes i know thanks.....i replaced the mass air relay and burn off....i also replaced the fuel pressure relay...are all these 3 relays the same..as in parts number ect.... a gentleman at the parts store said they're all three of the same units meaning I could put fuel pressure relay in the mass air flow sensor relay location because they're all the same relays..is this correct...?
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Old 03-10-2019, 05:17 PM
  #40  
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Hello Eddie77,

The fuel pump relay IS common with several applications on your 1988 Corvette, it also is used on the radiator fans I believe. I too have a 1988 and for a while it would just crank, make oil pressure but not run. It turned out to be a bad connector on the oil pressure switch behind the distributor. They claim you can limp home with a bad relay and I can tell you from my experience that little snippet is not true. Unless my car sees oil pressure while cranking the engine will not get ignition or fuel. I replaced the sensor to be sure but the connector was not crimped properly and was the "cause" of my car not running. I have not tried simulating the bad fuel pump relay and see if the engine will continue to run and make it home with a failed relay. If the relay is bad my car will not start, that much I do know.

Also check to be sure that your distributor is getting power, there is a clip on connector on the side of the distributor where I believe two wires attach. One is red and supplies power to the distributor. Bubba had messed that one up as well on my car.

Another exciting experience with my 1988 C4 was when I could get it started without sufficient flow of fuel and it would start and die seconds later. In the end my fuel supply line had corroded closed and I had to run a new supply fuel line from the tank to the engine. The way to find out if you have a corroded line is to measure the flow at timed periods. I measured the flow at the fuel pump outlet and compared it to what was coming out of my fuel supply line with a measuring container. Big difference. Be sure to look for crushed fuel lines that follow the passengers frame rail, I have seen it happen to Corvettes before as with crushed brake lines on the drivers frame rail.

Last but not least, what is the battery voltage? How old is the battery? Measure the battery first and then measure what voltages you are getting at the fuse panel. I have found a lot of cars get corrosion on the Battery positive post behind the battery under the side cover with gills. There is a large red wire that goes from the battery positive back to this particular post. My connectors were covered in corrosion and I took the outer nut off and cleaned each connector and then greased them all and re-assembled the stack of wires on that post. The wires that get their power at the post have fusible links built into them on my 1988. If that post is so dirty and corroded like that you are going to likely see a voltage drop as a result. Clean the battery connectors bright and shiny and then the post, after that I had to replace my fuses as the aluminum fuse block corroded as well causing even more problems like no power anywhere inside the car. After removing the radio I noticed the voltage coming into the accessories was very low like 10-11 volts. After a through electrical cleaning my car started right up and accessories started working that had not worked before.

Check the voltages at the plug for the fuel pump assembly. That can be found under the gas cap area. Fix any corrosion on anything electrical as quickly as possible.

If you want to reset your car's ECM then disconnect the ground wire not the positive wire. The last thing you want to do is "make" work for your self.
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