Car backfires/misfires and keeps cutting out-93 gto

Hi I’m new to this-first time Gto owner help!!
Ok I bought this Gto a couple of months ago-nightmare after the second day, thought it was exhaust so changed for straight through one,sounds good didn’t help, changed idle control valve-nothing!
Had compression test-40%leak in chamber 4.
Bit the built and got re-manufactured engine and did complete engine swap with new engine gasket set,stage 2 clutch and flywheel, new radiater, oil pressure switch and changed oil,fuel and air filter. All oils changed. The car ran fine on start up but now backfires, loses power and cuts out
What can it be???

Hi Neil and welcome to the club.

I’m no Guru on these cars but another avenue you could look at is the main ECU. There are a few people on here who have had similar experiences with the capacitors leaking and making a right mess. It could be this but i’m sure someone with a hell of a lot more experience with these cars might chime in. Sorry I couldn’t be more helpful, definitely worth a butchers though.



Hi Andy

Thanks for the welcome, I have heard a few people say this and that’s my next port of call but I hoping it’s something silly I’m missing as the money on this is just running away lol
I’m thinking air/fuel mix wrong, maybe O2 sensor as I removed it off exhaust when new one fitted??
Fuel injectors, the list goes on but thank you for your thoughts I’m on the case

On a different aspect, have you checked you intercooler / Vacuum hoses? I remember when I did my Cam Belt I forgot to put the rear turbo hose back on and I experienced the exact same thing. Sorry I should’ve mentioned earlier but only just remembered what an idiot I was for forgetting to put it back.

Welcome to the club dude. Off top of my head… Not a clue could be a multitude of things


Hope this helps, apologies if it sounds like I’m teaching you to suck eggs. Anyway. As Beanus mentioned check all your vacuum hoses, coil packs can cause this problem so try the dumb spark plug test to see if you can identify the misfire, check HT leads as they can deteriorate & cause an intermittent misfire, could be a fuel flow issue; try another fuel filter(removal & replacement guides are in the FAQ section of this site}. One of the most idiotic and simple cases of misfire is the rear earth lead that is connected at the back of the engine, trust me I know it is idiotic because i am n idiot & forgot to reconnect it on 2 occasions & felt a right muppet once I had checked everything else. ECU cap failures can only be diagnosed by removing the ECU & taking the top off to see if the capacitors have leaked. To break this situation down into simple terms the actual casing of the capacitors separate at their own will & mood, sometimes they behave sometimes they don’t as i mentioned the only way to cross this off your check list is the remove the ECU & inspect the internals(make sure you have a clean and earthed work bench when you inspect it}. This is by no means an exhaustive list of reasons, just my 2 peneth worth of years of GTO mishaps. Please feel free to ask as many questions as need be & I will do my best to help you out. On a positive note you are on the best site & forum to help you out with useful advice as there are a lot of people on here willing to help out. Hope that gives you some solice & comfort in your endeavours to rectify your issues.

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Again obvious one… If you’ve removed one O2 sensor that could be your issue right there :slight_smile:

Hi Neil

Welcome to the club. I am new to these cars too but I do have a fair bit of experience with turbocharged engines so I will list what I would do in your situation and hopefully something helps. Firstly it sounds like you are getting fuel in the exhaust. The back fire and the engine dying point to this. This could either be over fuelling or failure to ignite the fuel. Can you keep the engine running with a bit of throttle? If so is there any black smoke from the exhaust?

Best bet would be to go back to basics. Check vacuum hoses as mentioned above. A boost leak would cause the problems you are experiencing but it would have to be a fairly large one. It sounds like you are getting enough fuel so check ignition. Pull each plug and make sure each is firing when you crank it over. If you are getting a spark on each cylinder make sure it is happening at the right time. Mis timed spark could be quite complicated to fix if it is the actual timing. However it could be as simple as the HT leads being plugged in wrong so make sure they all go from the right port on the coil to the right plug.

If all that fails to solve the problem then look into the ECU. Its worth trying the cheap fixes first before doing the expensive one. Nothing worse than spending a grand fixing a car to find out you just needed a £20 spark plug. Try and get an ECU from a similar car that you can check on yours before forking out the money for a new one.

I wouldn’t rule the lack of an O2 out completely as its default mode without an O2 is to over fuel which is sounds like you are but I cant imagine it would over fuel that much to cause it not to run unless you were already over fuelling. In which case you still have an underlying problem even if replacing the O2 gets it running!

Hope something there helps and as I said I am still a newbie with these cars.


It was the O2 sensor in the exhaust, put a new one in and no issues at all!! Thanks for your the feedback guys

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Glad to hear you have her running. I am surprised that the missing O2 would cause that much of an issue. Normally it will just enrich the mixture enough to be safe and it will still run. I would suggest getting on a rolling road to check you aren’t running rich to begin with. Just to be on the safe side!

These cars are extremely fickle when parts are removed… The ecu would have noticed the sensor missing… Not gettin an O2 reading probably told itself to stop running (self preserving engine) lol :slight_smile: glad it was a simple fix :slight_smile:

Ah ok fair enough. Like I said I am new to these engines and was basing it on what I know from my silvia and the various Honda’s and Subaru’s I have worked on.


Welcome to GTOUK, glad you got your problem sorted, nice looking car get some photos up when you get a chance.


Sorry to hear you start out with GTO ownership didn’t go too smoothly . Good to hear your up and running now though

Welcome aboard :sunglasses:

Craig :smile: