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Author Topic: Guzzling fuel and warm start issues  (Read 3270 times)

Offline bigdaves12

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Guzzling fuel and warm start issues
« on: 06:47:04 PM / 16-Jun-14 »
Hi all I'm mainly on the uk forum but thought I'd get some opinions from the US club!

I've recently bought my 2nd s12, stock ca18et. It ran like crap when I drove it home, no power at all, backfiring like crazy when accelerating but nevertheless drove a full 200 miles nice and slowly :)

I've now sorted all that out, timed up, plugs changed and accelerates fine. Drove it around for a day or so on friday. I put a half tank of fuel in it and only got around 50 miles which is ridiculous. works out to around 11mpg.

It does smell like its running rich. when I was giving the car a good looking over I tested the maf, coil, transistor, installed a new thermostat, fuel filter and air filter along with spark plugs. I'm dying to make this my daily but can't be putting that much fuel in it when I do 60 miles a day to work and back.

2nd issue is I get intermittent no spark when starting up and it did cut out on me a couple of times when driving at operating temperature too. I checked ECU codes and it kept throwing 21 for ignition. Took the multimeter and traced the wiring and checked everything which was fine but it still kept throwing code 21 even after clearing. Replaced the ECU with one from my old et setup from my other s12 and it no longer throws the code but I still get intermittent spark when starting up after a drive.

According to the FSM: (Check out my pb for pics of my s12s)



Both the dizzy and transistor should be connected directly to ignition from the barrell but when I checked continuity directly from the barrell to both, only the transistor showed continuity to ignition and not the diizzy?! I tried to jump ignition from the transistor to the dizzy but that just turned the ignition on permanently without having the key in ignition position which confuses the hell out of me. Is there a sperate relay to give power to the dizzy?

I saw the post by Kerberos_8 about random dying at operating temperature but I couldn't get the optical sens out of the dizzy without breaking it off so i left it for now.

The fuelling issue is what I want to figure out first and foremost, any advice at all is appreciated!

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Offline rednucleus

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Re: Guzzling fuel and warm start issues
« Reply #1 on: 08:06:33 PM / 16-Jun-14 »
What year?

Offline sideways_s12

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Re: Guzzling fuel and warm start issues
« Reply #2 on: 09:19:12 PM / 16-Jun-14 »
CHeck you cts Coolant temp sensor it may be on the way out when they are bad or unplugged the car will run while in cold start mode but then die once warm. Seeing how yours is intermittent I would say it maybe on it's way out. check the plug as well. As for running really rich the only thing I can think of is a stuck injector.

Offline bigdaves12

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Re: Guzzling fuel and warm start issues
« Reply #3 on: 11:23:36 PM / 16-Jun-14 »
What year?

Sorry I should have said, 86 auto

CHeck you cts Coolant temp sensor it may be on the way out when they are bad or unplugged the car will run while in cold start mode but then die once warm. Seeing how yours is intermittent I would say it maybe on it's way out. check the plug as well. As for running really rich the only thing I can think of is a stuck injector.

I'll replace the cts first thing on Friday. Is there a definitive way test injectors?

Thanks for the swift replies!

Offline sideways_s12

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Re: Guzzling fuel and warm start issues
« Reply #4 on: 06:18:12 AM / 18-Jun-14 »
I know how.to.find a bad one if its running on 3 but if its stuck open I'm not sure short of pulling the rail...

Offline bigdaves12

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Re: Guzzling fuel and warm start issues
« Reply #5 on: 06:45:46 AM / 18-Jun-14 »
Ordered the sensor, might pull the rail tonight and just prime the fuel pump see if any of them are leaking

Offline BOSSMAN

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Re: Guzzling fuel and warm start issues
« Reply #6 on: 12:00:38 AM / 20-Jun-14 »
Check for a leaky fuel pressure regulator, might have a pin hole in the diaphragm and the extra fuel would run back through the vacuum line into the intake manifold.
86 CA18ET....owner since 1990.
The name is Bossman, but you can call me Mr. Panda....My other car is a Buick....
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Offline bigdaves12

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Re: Guzzling fuel and warm start issues
« Reply #7 on: 11:29:24 PM / 23-Jun-14 »
So i pulled the fuel rail and primed it, none of the injectors are stuck open so thats ok. I had no fuel pressure gauge to diagnose anything so  i replaced the fuel rail along with the fuel pressure regulator, stuck the known good injectors on but I don't think its made a difference. I took it to work yesterday which is mainly long run 50 to 75 mph constant 50 25 miles each way and only managed 18mpg. That was with very light acceleration and sensible as hell driving, is that right? Surely it can't be this bad on fuel economy!

Check for a leaky fuel pressure regulator, might have a pin hole in the diaphragm and the extra fuel would run back through the vacuum line into the intake manifold.

BOSSMAN how would I check this dude?
« Last Edit: 11:32:52 PM / 23-Jun-14 by bigdaves12 »

Offline Cajun1guy

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Re: Guzzling fuel and warm start issues
« Reply #8 on: 12:31:41 PM / 24-Jun-14 »
Mine regularly gets 28-30 mpg on highway driving. Almost as good as my Kawasaki Vulcan!

Offline Basic

Re: Guzzling fuel and warm start issues
« Reply #9 on: 01:05:43 PM / 24-Jun-14 »
you would hook a vacuum source to the Fuel pressure reg with the pump on and primed. Something like this hooked to the vacuum port -
http://www.harborfreight.com/brake-bleeder-and-vacuum-pump-kit-69328.html

Run fuel pump (u can actually start the car) - then apply vacuum - Watch line for fuel.


Also - check your fuel pressure at idle, both normal and with the line to the regulator pinched off. if the regulator is working correctly the pressure will increase with the line pinched off.

Hey, truck engine + truck turbo - why not?

Offline bigdaves12

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Re: Guzzling fuel and warm start issues
« Reply #10 on: 06:27:36 PM / 24-Jun-14 »
you would hook a vacuum source to the Fuel pressure reg with the pump on and primed. Something like this hooked to the vacuum port -
http://www.harborfreight.com/brake-bleeder-and-vacuum-pump-kit-69328.html

Run fuel pump (u can actually start the car) - then apply vacuum - Watch line for fuel.


Also - check your fuel pressure at idle, both normal and with the line to the regulator pinched off. if the regulator is working correctly the pressure will increase with the line pinched off.




Awesome, just ordered a pump just like the one in the link thanks Basic

In the morning today, started up, drove to gas station and fueled up car started fine and began driving to work. Was thrashing it a little and started to cut out and eventually cut out all together just as i pulled over. Didn't start back up for around 5/10 mins and then sarted fine and drove to work.

Drove home from work 12 hours later with no issues. Attempted to start up after a couple of hours but no spark GRRR this is not the first time. I have had intermittent spark on starting back up a few times. Any ideas fella I'm dying to drive regularly but cant with these issues!

Offline Cajun1guy

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Re: Guzzling fuel and warm start issues
« Reply #11 on: 12:53:57 PM / 27-Jun-14 »
Check the ECU for codes. Spark issue might be a pickup going bad in the dizzy? You're sure it's spark? Or could your fuel pump be getting intermittent? So many things, so little time...

Offline bigdaves12

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Re: Guzzling fuel and warm start issues
« Reply #12 on: 05:08:26 PM / 27-Jun-14 »
Check the e ECU for codes. Spark issue might be a pickup going bad in the dizzy? You're sure it's spark? Or could your fuel pump be getting intermittent? So many things, so little time...

I have a spark plug tester plugged into cylinder 1 so I can see if it sparks. Definitely no spark.

I've taken apart a dizzy in attempt to follow kerberos sticky in this section and clean it out but no idea whether his dizzy was same as mine. I've posted some pics in the thread, just waiting for a reply
« Last Edit: 05:09:07 PM / 27-Jun-14 by bigdaves12 »

Offline bigdaves12

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Re: Guzzling fuel and warm start issues
« Reply #13 on: 09:10:47 PM / 29-Jun-14 »
UPDATE: I've installed a new dizzy, times it all up and will be testing it over the next few days. Its idles much smoother now than before so hopefully it was just the dizzy... will keep you guys updated. Thanks so much for the input!
« Last Edit: 09:11:19 PM / 29-Jun-14 by bigdaves12 »

Offline BOSSMAN

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Re: Guzzling fuel and warm start issues
« Reply #14 on: 07:36:58 PM / 30-Jun-14 »
Since you replaced the fuel pressure regulator then you can rule that out but for reference just pull the vacuum line out with system under pressure , if there is a leak you should see the coming out the vacuum line.
86 CA18ET....owner since 1990.
The name is Bossman, but you can call me Mr. Panda....My other car is a Buick....
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Offline bigdaves12

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Re: Guzzling fuel and warm start issues
« Reply #15 on: 07:47:01 PM / 04-Jul-14 »
Since you replaced the fuel pressure regulator then you can rule that out but for reference just pull the vacuum line out with system under pressure , if there is a leak you should see the coming out the vacuum line.

No leak bossman, its all good.

I've put around 200 miles on it in the last few days, averaged 27.3 mpg HELL YH thats so much better!

Thanks so much guys

Offline Cajun1guy

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Re: Guzzling fuel and warm start issues
« Reply #16 on: 01:33:24 PM / 08-Jul-14 »
Alright! Let's hear it for success! I hope it gives you great service brother, mine has been a daily driver for years.

Offline sideways_s12

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Re: Guzzling fuel and warm start issues
« Reply #17 on: 12:19:25 AM / 14-Jul-14 »
Nice job! Glad you got it fixed.

Offline bigdaves12

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Re: Guzzling fuel and warm start issues
« Reply #18 on: 09:44:31 AM / 23-Jul-14 »
Thanks fellas, it's awesome but not as awesome as it would be to have my mk2 on the road. My money is tied up in this one so sadly it's up for sale :-(

At least I'm confident it's in good working order when it comes to selling it!