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George H.
George H., ASE Certified Technician
Category: Car
Satisfied Customers: 18768
Experience:  ASE Master Tech 15+ yrs, AAS Automotive Technology, Factory trained Asian specialist
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My 1999 Hyundai ELANTRA cranks but will not start. It is not

Customer Question

My 1999 Hyundai ELANTRA cranks but will not start. It is not getting power to the fuel pump and the shop that is working on it cant seem to be able to figure it out. They cannot get their scan tool to connect to the cars computer to diagnose it. Anyone have any ideas? Thanks in advance for any/all help on what could cause this situation! Any fuel pump wiring diagrams would help also.
Submitted: 7 years ago.
Category: Car
Expert:  George H. replied 7 years ago.

Hello I will help you with your question,


If they cannot communicate with the computer and there is power and ground to the computer and the diagnostic connector it is likely that the computer has failed. To troubleshoot a computer failure you ensure that all inputs are correct, no output wiring orcomponents are pulling the output down to 0 volts and if the outputs are incorrect the computer is the problem. There is no direct test to confirm the computer as the source of the problem.


In your case after checking the power and grounds I would check the signal from the crankshaft position sensor, the fuel pump relay and the voltage and signal at the MAF sensor. I would unplug any sensors that may pull down the supply voltage from the computer such as the TPS, Oxygen sensors and the Idle air control, purge valve and the transmission control computer. The Engine computer is mounted in a very inconvienent place above the left kick panel under the dash with the transmission computer blocking access.


Once the trans computer and the sensors and actuators are disconnected, the crank pulse signal verified I would check for spark and signal to the ignition coil as this is a basic control from the computer. If no siganal to the computer and spark at the plugs the computer has failed.


Here is a system diagram that will give you an overview of what is involved




Turning the fuel pump on is a simple matter of removing the fuel pump relay and using a paperclip to bridge the connection long enough to determine that the injectors are being pulsed. If the injectors are not recieving a pulse signal you are back to the crank sensor signal and the computer. Once you have those it is a simple matter to ensure thast the fuel pump is turning on as directed.


Here is the fuel pump diagram but I would not start here unless I was sure the computer was intact. I had one a week ago that ran but I had no communication with the scantool unless I unplugged the transmission computer. I found that the trans computer had been replaced with a junkyard unit and it was incorrect for that vehicle




I will be happy to provide any diagrams/information you need to resolve this. Please have them check the power/ground at the computer, diagnostic connector and the crank signal at the computer


Let me know what I can do to help you with this


Thank you



Customer: replied 7 years ago.

I am so sorry that it has taken me so long to get back with you. I got very sick and wasnt able to do anything.


However, I printed off the info that you gave me and gave it to the mechanics at the shop that morning. Well they changed he crank sensor and it didnt help.


I am a mechanic myself but I am a Diesel/Generator mechanic. Not a car mechanic. I do not have much experience on Import vehicles but I drug my car away from the shop and started working on it myself anyways.


I have spark at the plugs. The fuel pump works but does not come on unless you send direct power to it.


I have no injector pluse on 2 injectors but I do on the other 2. While cranking I smell fuel very strongly inside the vehicle & out.


They disconnected the factory alarm system thinking it was the problem and I reconnected the original connectors and left the alarm out.


When I pulled the tranny ECU ( LikemYou Said) I was able to get the scantool to work. I have a brand new OTC Nemisys and on live data it is displaying : fuel system#1 Ready/Active fuel system #2 disabled.


There are no codes showing up on the scantool.


Also its not recieving any inputs. Like when I press the throttle the scantool shows 7% throttle constantly and never changes no matter how far I push the pedal or how many times I push it.


Any time I reconnect the tranny ECU the scantool will not access the engine CPU.


I do not know how to check the engine Computer to see if it is getting power or ground because I dont have the diagrams but I assume it is because I am able to read it now and I do have power at certian points on the OBDII connector.


They did pull half the dash and the Instriment Cluster which I have not reinstalled but I wouldnt think that would keep it from starting would it?


Now thats wher i am at with this car.

Customer: replied 7 years ago.
I will be more than happy to pay you if I can get this thing going with your advice. Also I clicked on $58 not $23. I dont know why thats all they took as a deposit because your advice is worth much more to me than $23 and I know you time is worth more than that. So if I can get the info I need to fix this situation and there is any way to change how much I pay, then please let me know what to do and I will certainly change the $ to what you think the info is worth.......
Expert:  George H. replied 7 years ago.

Well you have a starting point...


You will have to determine why the computer is not showing you any change in the input data. I have not used the nemisys but have used the genisys so it should be almost the same.


If you turn the key off while connected to the computer does the screen say lost communication or does the data freeze or it might dissapear but the data PIDs are still listed. This may be a clkue that all you need to do is reinitialize the communication with the computer to get fresh data. A good check is to unplug the Intake air temp sensor or the coolant temp sensor and the data should go to -40 or -34 depending on which operating system is loaded in your computer.


The TPS is a good check also but the other two can be used as backups.


If you have good spark that is half the battle but the computer provides ground for the injectors and the drivers in the computer may have failed. You need a good strong spark though. The crank sensor tell the computer when to spark and when to inject so that part is working.


One check is from the case of the computer to ground while the engine is cranking. Anything more than about .2volts is cause to suspect the computer.


Leave the tranny computer disconnected for now it is the last issue to address.


Watch the injector pulse width and see if it changes while cranking, it should go from 50ms or so to 16ms or so. Your tool may not read in ms though.



I am happy with the amount you have offered but you are always welcome to add a bonus at the end if you think I deserve it.


This is enough for now, I will be happy to work with you for as long as it takes so be prepared to do some troubleshooting.



Let me know what you find with the case to ground test and I will read the manual for the Nemisys so that I can get an idea of what PIDS are available to you



Customer: replied 7 years ago.

Okay, this is what I've done. I connected the scantool and disconected all the inputs. The TPS still reads 7% disconnected it also reads 7% connected even when pushing the throttle.


All others did the same thing except for the CTS. It went to -40deg like you said. But 4 sum reson the scantool is reading the spark advance at 63deg constantly even though the car isn't running and also while cranking it doesn't show the rpm's on the scanner when it normally does.


IAT stays at 61 deg even though its 40 or below in my garage.


When I turn key off it shows no data. It still has the pid's up but says "No Data Avaliable".


As far as the computer ground test I got 0.03 volts on my Fluke Meter while cranking and 0.00v not cranking using a BATTERY Ground. Using Body ground I got 0.00v non-cranking and cranking.


I dont know why I tried this but I dont understand it and if its irrelevant, then forget i mentioned it. I just didn't know if you needed to know ths info. I set my meter to ohms and touched the red lead to computer box and black to body ground directly behind it and got 1.1 ohms with no change while cranking.(seems like a lot of resistance to me seeing that the box is bolted and grounded 2 inches away.) Again I touch the red lead of the meter to the comp. box and black lead this time to BATTERY ground and RECIEVED 9.8 OHMS then while cranking it flucuated between 75 and 87.3 ohms.


As you know, I'm no expert but I've worked on my share of vehicles over the years and I know most people, mainly techs, are quick to say the ECM is the problem. But the fact is they rarely go bad. I've seen only a handfull that were actually bad and even at that most of them were repairable by replacing a prom or flashing it to reset it.(Domestic) I don't know about Imports.


But with what I have seen with this car I cant come up with any other conclusion.



I cant just go buy a comuter around here to swap it and see if its the problem then take it back if not. I have to order it from the dealer and its a non-returnable item.


I dont want to pay for something I do not need but i've got to get this car running!


Junk Yard? Or do you have a better idea? FYI I checked the injector pluse with a noid light. Not my scanner and only 2 work. Also the scanner still says "Fuel System Bank 1 Open" ---- "Fuel System Bank 2 Disabled".


I also do not understand the tranny ECU causing me to lose comm with the Engine ECU. It's not from a junkyard . It has no marks or paint on it like they usually put on them.


Could the Alarm system have anything to do with it? It is a factory alarm and says Hyundai on it but looks like it was installed non-factory. Like an aftermarket alarm with a siren under the hood and red indicator light installed on top of the steering collum pannel. Does it shut down the fuel system or just a deterrent?


Oh I did change the fuel pump and ECU relays just to make sure with no luck :-(. Please Help! And thanks for your patients and help.

Expert:  George H. replied 7 years ago.

OK you have been busy,


The alarm is a port installed system and that is why it looks aftermarket. It does not control the fuel only the start relay so the cranking is inhibited. You only have one fuel system that is why the second is disabled. Be sure you have power to all the injectors with the key on it all comes through the same relay and there is a splice just before the fuel rail that feeds the injectors.


Here is a set of diagrams of the computer and the control systems but I am comming to the same conclusion as you is that you need a computer. A boneyard one will work fine if you can find one. Try to help you find one near you. Don't use any of the rebuilding services that post there though they are junk.\


Last test before condeming the computer, unplug the oxygen sensors, the Idle air control and the purge valve. I think the purge valve was on the drivers fender on this year if not it is just below the throttle body.


With these unplugged see if all injectors get a pulse. Also the plugs may be carboned up by this time is so put in a set of new.














And the alarm wiring




The way your meter works to measure resistance is it applies 1.5 volts to the circuit and measures what it gets back. This is why if you have a little voltage already in the circuit you will show resistance where none exists. Unless you measure for voltage first you can't really trust what you see back


You have a strong blue spark?


If so and the injectors still only have two pulsing with the O2 and IAC unplugged and no codes it is time to pull the plug on a new (or different) computer. Here is a pinout for the ECM it may be hard to see the numbering








Let me know what you find







Customer: replied 7 years ago.
Yeah, the purge valve is on the fender. I did exactly that earlier and still had only 2 injectors pulsing.... Thanks for all the info. Im gonna print all this out and go over everything again. Hopefully I will find a wire frayed, burned or broken. If not I'll let you know. Whatever I find I'll let you know. When I'm done I will Accept ur help 2 get you paid and I guess I'll be off to the U-Pull-It.... I really appreaciate your profesionalisim, quick responses, help and patients.
Expert:  George H. replied 7 years ago.

I will be here when you have further questions, please let me know how I can help