1980 GTSi Backfire/Power Issue

Hello everyone, I would just like to start by saying this has been an incredibly helpful, informative and supporting forum, and unfortunately I think I may need some help.

I have a 1980 2v NA GTSi that has decided to give me a bit of trouble.

A bit of background:

Since I have had it (Aug 2020) it has been a tough warm start, always required some accelerator pedal pressing to get it to catch on start up; when cold absolutely no issue, it also seems to run a little rich, more so when cold but maybe that’s just normal for these machines. This car did have a very thorough going over about 12 yrs ago by Paul Newman and was well cared for since then.

The Issue:

I was driving down a rural highway about 30 min into a Sunday drive when I drove through a huge dust cloud thrown up by an oncoming farm tractor (not sure if relevant). Once I passed through the cloud there was a huge backfire, then a constant stream of backfires, worse when under load, and a corresponding decrease in power.

The slowdown lights didn’t come on, oil/engine temp was around 200, water temp about the same.

When stopped at lights as I was limping it home, idle was quite rough and around 600 rpm, normally it’s around 900 and smooth. No backfires while idling, or when I was coasting with clutch in going down hills, but pretty continuous with any accelerator pedal use.

I got it home, parked it and then the next day started it up to try to troubleshoot.

Well everything was perfectly fine.

Started right up, took it out for a short drive (didn’t want to get stranded) felt maybe a little decrease in power (wasn’t quite as lively at lower rpm (below 4000) but maybe that was just me over thinking it.

Now I’m not sure what I should do next.

To me it seemed like I lost a bank for whatever reason (rough idle and low power) and all the undetonated fuel was leading to the backfires, but would it be ignition based or fuel supply based, and why did it correct itself?

Could this be due to difference in temperature with a component that’s trying to die?

Is it a coil on its way out?

I’m not sure how to take the next step without getting over my head too quickly.

If anyone has had a similar experience or has some suggestions to aid identifying the issue I would greatly appreciate it.


Thanks in advance,


Mark

 

Thank you all for the quick and helpful replies.

Absolutely correct. I just wanted to give a bit of background to when the last major overhaul was done and potentially what could be problematic now.

I believe this too, but I really don't know that much about these wonderful creations and didn't want to potentially ignore a stuck injector or something along those lines.

18 months sounds scary.

As indicated, I'm just starting in the world of car mechanical adventurism and I think I'll need a bit training (YouTube, friendly neighbours, etc.) as well as amassing an appropriate work bench to tackle some of these things.

 

I looked at all the extenders, I will have to purchase an appropriate plug socket to get the plugs out, but I didn't see anything that looked like burning arcs. Almost all had a weird yellowish colour on one side of them. Not sure what that's about.
The wires/extenders seemed to have a fair bit of play in all of them, didn't think they would be that wiggly, I guess that's normal.
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This is what it currently sounds like on startup which is pretty much unchanged since I've had it.
I guess I'll do some driving and try to recapitulate the issue and this time record it.

 

Thanks!!! I'll check my kit.


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Update:
It’s been awhile but I finally got it to fail again last week, same rough idle with backfires

Neighbour had a timing light at hand so we checked all the plug lines and everything looked good suggesting it was post coils and plug wires (extender, spark plug itself, fuel delivery).
I swapped out the plugs and extenders yesterday and found plug 8 had tonnes of carbon, and extender 3 was cracked.

Plan to put on a bunch of miles if the weather will cooperate and reassess plug 8 and try to figure out the underlying issue.

Thanks so much for all the help.


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Nice chart! Thank you.

I was definitely having warm start issues as well, never cold start issues though. I unplugged the thermo-time switch and the warm start issues ceased. I’m guessing the thermo-time switch had failed in the closed setting, continuing the current to the cold start injector so there was continual injection of “extra” fuel leading to the hot start issue. I’m looking to replace it now but the availability and price of thermo-time switches is suboptimal (for another day).
I would have thought all plugs would have been blackened though if it was a too rich situation, not just cylinder 1. All seven other plugs looked fairly good, 8 may have been a bit white and it was tight as hell getting it out.

Addendum: I messed up in post #13 with my numbering, it was cylinder 1 with the dirty plug and cylinder 6 with the bad extender.


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Went for a nice spirited drive today, not too warm out (mid 20s) water was at 195 almost whole time with oil at 210. After about 60 minute drive stopped for gas, car ran beautifully whole time. When I restarted to leave the gas station the dreaded misfiring/backfiring was back. Pulled over restarted the car 5 times, always had the misfire/backfire happening. Slowly made my way home, seemed to backfire less in higher gears irrespective of throttle position, parked it for an hour, restarted and it ran perfectly.

Since the last time this happened I replaced all the extenders, and plugs but I guess that wasn’t the issue.

Anybody have any thoughts/guesses.

To recap:
- intermittent loss of power (can be months in between episodes), sometimes while driving but also after restarting.
- seems to be when car has been run for longer/hotter drives
- timing light illuminates on all eight plug wires suggesting electricity is getting to each plug while misfiring is happening
- recently replaced extenders and plugs and still happening

Any suggestions as to next diagnostic tests to take/parts to replace would great.

Thanks for reading.

 

Definitely the plan for first light tomorrow.
I will report back.
Thanks.

 

Plugs have less than 500 km on them and cylinder 1 was very dark while the others were all similar/normal.

I would guess from this that cylinder 1 is the problem cylinder that stops firing when I have the backfiring issues.

But why?

Is the plug fouling the cause or the effect?

I haven’t tested the wires yet, I was considering just replacing them all as I don’t know when the last time that was done and it probably won’t hurt to do it.

Any other suggestions of things to look at?

Thanks

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I put another new plug in today. All the extenders were replaced when I replaced the plugs in October last year. Since October I’ve put on less than 500km and it ran perfectly for all that time until yesterday.

I’ll order new wires and I’ll check the plugs after a hundred km or so and see what it’s like.

The thing I don’t understand is why does it run perfectly most of the time, then when it drops the cylinder I still get timing light flashing on that plug wire. The new extender looked perfect on that plug with no arcing or cracks.

 

The car started back up perfectly yesterday about 1hr after I got home.
It started perfectly well this morning too while I pulled it out of the garage to check the plugs.
I haven’t tried changing a plug right when it happens. I’ll keep one in the car for next time.

I drove for about 15 min with it backfiring to get home yesterday and I’m guessing that’s why the plug is so soiled, but again why did it stop in the first place? I guess it could be the plug wire causing the fail, then it restarts sending electrical info, but the plug is so fouled it doesn’t fire. But then why does it start perfectly an hour later?

I go through about a quart of oil a season so roughly 2500km, there are small leaks from the car too, another story…