Hyundai Hatchback with LPG sequential kit jerks and turns off while on the move

Hi All, This is my first post in Cartalk. I own a Hyundai hatchback which i converted to a LPG sequential kit 6 months back. The car was running fine till a couple of weeks back. Now I experience jerking at 2nd and 3rd gear and sometimes the engine just turns off while on the move at these lower gears or if the car encounters a pothole(I then have to restart the engine ).
So far, I’ve changed the ignition coil(6 months back) and spark plugs(1 week back) but I still experience the problem.
The Hyundai mechanic says that it could be a problem either with the wiring to the ECU( since soldering instead of couplers have been used) or with the injectors. He says the cord wires and ignition coils are just fine.

The Lovato authorized mechanic who fitted the LPG sequential kit says that it could be a problem with the spark plug cord wires or the ignition coil.

The reason I don’t see a rationale with the Hyundai mechanic’s argument is that the car has been running perfectly for 7 months. Initially , when the car was fitted with the LPG sequential kit, there was a slight jerking problem but was gone once I got the ignition coil replaced.

The reason I don’t see a rationale with the LPG mechanic is that the ignition coil is just 6 months ( 4k kms ) old.

I’ve been struggling with this problem for a while since each mechanic is giving his own version of the problem. I might be wrong in my rationale above.

Appreciate your advice/pointers to get the problem rectified

If the jerking and shock from a pothole is causing the car to shut off, I’d guess a bad circuit connection somewhere. This could be anywhere on the car, but, since the LPG kit was an add-on, I’d concentrate on the electrical connections related to the kit. To run on LPG, the control circuits would cut the pulse signal to the fuel injectors and possibly adjust the ignition timing. So, the kit would probably include wire splices into the harness controlling these signals. That is where I’d start.

Thanks BustedKnuckles…will check with the mechanic about it! Had a question(sorry if it is naive): will the electrical connections become faulty over a period of time?? Because everything was working fine when the LPG kit was fitted

It depends on the method of slicing the wires. Some are more prone to later failure than others, but I’ve seen enough wire splice failures to say 'Yes, they can become faulty over time."

It might be worthwhile to put on a glove and do some wiggling of all the wires, especially associated with the add-on system, while the car is running to see if you can get it to cut out or misbehave. Is the check engine light on and have the diagnostic codes (including pending codes) been checked? If you’re just going to throw parts at it, I’d probably start with the crankshaft position sensor, as a bad one of these will cause stalling, jerking, and will not set a trouble code in a lot of cases.

Things deteriorate over time, so yes, a loose connection can develop months after the system was installed.

Thank you oblivion and texases!
@ oblivion: yes the check engine light is on and the Hyundai service center personnel told me that they had run the diagnostics and nothing seems wrong with the code. He also mentioned that anything that is wrong with the LPG kit will not show up in their codes

@maggy: “the Hyundai service center personnel told me that they had run the diagnostics and nothing seems wrong with the code” That the check engine light is on means there IS a stored trouble code. If they’re saying “there is nothing wrong with the code”, that doesn’t make any sense. Would you have the code that they detected? Things that are wrong with the LPG kit may not generate trouble codes since it is an add-on and is not integrated into the computer’s diagnostics, but any codes that are set may give some hint as to what the problem is or where to investigate further.

I think what they meant was that they ran all the diagnostics tests listed in the service manual associated with the code and it passed all the tests. All of those tests are for systems installed on the vehicle at the factory, they do not have procedures for after market equipment. The LPG equipment manufacturer should have separate procedures for additional troubleshooting of the code.

If you can get the code, post it here. Maybe someone can help. The code will be a P followed by 4 numbers, i.e. P0300.

I’ve converted many cars, trucks, and even one motorcycle to propane. The one recurring problem was that if your coil, distributor and plug wires weren’t in perfect condition it would cause a misfire. Propane is an excellent fuel with 105+ octane and your oil stays clean almost forever but any flaws in the high voltage side will show up quickly.

Thank you everyone for the insights. My bad…the engine check light wasn’t on. I took the car to the Hyundai service center again. The mechanic at the Hyundai service center had run the diagnostics and he confirmed that there was no problem with the codes.
Now comes the interesting part: He then gave a direct line to the injector from the original EMU bypassing the ECU of the LPG kit. When we drove the car now, the engine didn’t stall or jerk. When he now reverted the connections to now include the ECU from the LPG kit, the engine as expected started stalling.
He informed me that this is a problem with either the ECU or the connections to the ECU. He ran some tests and confirmed that the injector isn’t pumping fuel enough fuel. I am not sure what this means.
Should I now take it to the LPG service center guy and what should I ask him to check? I think he is facing this problem for the first time and hence he is sticking to the traditional ways of getting the spark plugs, ignition coil and plug wires replaced of which I have done the first two.

Well, the test has isolated the problem to the ECU of the LPG kit. The ECU turns the injector on and off to regulate how much LPG is injected to the engine. Right now, it is not sending enough, and the lack of fuel is causing your problems. By bypassing the ECU, he basically rigged the injector on. This confirmed the rest of the fuel system is OK, but you don’t want to drive around like that all the time because your wasting a lot of LPG that way. So, if the LPG tech insists on sticking to the coil, plugs, and wires, you know he’s soaking you or doesn’t have a clue. Basically, the LPG ECU needs to be tested and fixed.

Best case, it might be a problem with the wiring to the LPG ECU. Have you tried the ‘wiggle the wires’ test, concentrating on those associated with the LPG ECU?

If it’s not the wiring, the LPG tech should swap in a known good ECU and see if that fixes it.

@Kriley: I have the problem with most LPG as well as petrol. Pardon my ignorance…if it was a problem with the voltage side, I was wondering whether it should be felt more in LPG and less on petrol which is not the case…Please advise

Thanks BustedKnuckles and texases! will try my hand at wiggling with the wires tomorrow before taking it to the LPG mechanic

The shop that installed the LPG kit should guarantee the parts and labor for one year.

I say should because I’m not sure if there are rules about this.

Apologies for the delayed response…I wanted to make sure that the fix is working properly …and fortunately it has been working properly for the past 3 months!
So here is the update since my last post:

  • The car started jerking even when the LPG kit was totally dismantled and the car was running on petrol by connecting the original ECU to control the injectors. This proved that there was something wrong with the original setup and not the LPG kit.
  • The Hyundai service men found the problem to be clogged injectors. They cleaned the injectors and the car started running smoothly like a charm. The service men finally told me that they think the root cause of the problem might be due to my fuel usage. I generally fill both my petrol and LPG tanks fully and it takes atleast 2-3 months to run the car till the tanks are empty. So petrol gets stale and slowly starts affecting the injectors…Same is the case with LPG
  • I’ve refitted the LPG kit. Now I fill the fuel tanks just enough to empty them in a week or two. And the car has been running absolutely fine with no problems.
  • The only problem that I face at this point is that when it rains, there is a jerk which I guess is probably because water gets into the couplers used for the LPG electrical connections. So I am good with that for now…The major jerking headache is now off my head

I got to thank you guys for providing me a lot of advice and insights. Totally appreciate it.
I am sure there would be many others out there who would be facing a similar problem as I faced earlier and this thread might serve as a bible for them hopefully :slight_smile: