Misfire, Shuddering/shaking, lopey idle... (1 Viewer)

[BlueCruiser84]

Possible discovery?

Have you done a dynamic compression check? I am not thinking head gasket but more a sticky or leaking valve, both would be very noticable at idle but would be hidden at higher engine revs.

regards


Dave

No, I have not done a compression test yet.


HOWEVER, I went down and was checking all the wires again to make sure they had spark and while I was at it I was checking fuses. I noticed that the EFI main relay was incredibly hot. So, per the FSM I tested it and I had no continuity between post 1 and 3, but when I put 12 volts to them I could hear the relay click... interesting.

I'm guessing that a new relay is in order because I had no continuity between terminals 1 and 3.

How does this sound to everyone? Seems like it could be a likely culprit.

Can anyone give me the clliff notes on how this thing works?

 

[Dave 2000]

I do not get to work on many gas 80's however, I doubt that is the problem because the relay keeps the fuel pump on. If the relay was 'dropping out' the engine would simply stop.

If it is cheap enough give it a go,

regards

Dave

 

[BlueCruiser84]

I do not get to work on many gas 80's however, I doubt that is the problem because the relay keeps the fuel pump on. If the relay was 'dropping out' the engine would simply stop.

If it is cheap enough give it a go,

regards

Dave

Daaave, why would you shatter my hopes that way?? I got one on order from Toyota so I will report back once it is in.

The relay functions (it clicks when I give it twelve volts) but it does not have continuity. I'm thinking that for some reason the straight 12 volts is enough to activate the relay but there is enough resistance inside the relay between terminals 1 and 3 that it is not working properly.

Then again this is my first ever venture at electrical trouble shooting.

 

[kidglove13]

HAve you completely ruled out the O2's?
I am taking a stab at it, but from what you said it seems that you are running rich with the strong gas smelling exhaust

 

[Dave 2000]

Sorry Bluecruiser but IIRC the relay gets an initial 12v to run the fuel pump for a couple of seconds to pre-pressurise the fuel line at the injectors, then when you crank the relay it gets another trigger from the ECU or crank sensor to tell the pump to keep running. The idea is if the car is involved in an accident the fuel pump will not continue to run if the engine is stalled and/or the interia switch is tripped.

Assuming I have that right (please someone with more knowledge correct me I if I am wrong), if you had a weak fuel pump then your car would not run better at speed but more likely the reverse i.e. the fuel demand would be higher and a failing pump (or relay) would not keep up with the demand.

I have seen relays that will pre pressurise the fuel line so the engine fires but then it cuts out right away as the relay is not getting or responding to the crank or run signal.

Let 'us' know how you get on, it is important that I along with other forum members see a resolution as it may be helpful in the future.

regards

Dave

 

[BlueCruiser84]

HAve you completely ruled out the O2's?
I am taking a stab at it, but from what you said it seems that you are running rich with the strong gas smelling exhaust

I have not ruled out the O2 sensors yet. I seriously doubt they are causing this but I will go hit them with the multimeter when I get home today. The way this thing is running it sounds like it is dropping half the cylinders... which could be oxygen sensor related?

Are the test for the O@ sensors definitive? or could it test correctly but still not work? I had originally suspected oxygen sensors, but it wasn't throwing a code and after doing some research it seemed like they were further down on my list of things to check. Now I am wondering if I shouldn't have checked them first. I guess if one was bad it could be making 3 cylinders run either rich or lean?

Sorry Bluecruiser but IIRC the relay gets an initial 12v to run the fuel pump for a couple of seconds to pre-pressurise the fuel line at the injectors, then when you crank the relay it gets another trigger from the ECU or crank sensor to tell the pump to keep running. The idea is if the car is involved in an accident the fuel pump will not continue to run if the engine is stalled and/or the interia switch is tripped.

Assuming I have that right (please someone with more knowledge correct me I if I am wrong), if you had a weak fuel pump then your car would not run better at speed but more likely the reverse i.e. the fuel demand would be higher and a failing pump (or relay) would not keep up with the demand.

I have seen relays that will pre pressurise the fuel line so the engine fires but then it cuts out right away as the relay is not getting or responding to the crank or run signal.

Let 'us' know how you get on, it is important that I along with other forum members see a resolution as it may be helpful in the future.

regards

Dave

After reading up on it some more it seems like it is either a work/not work thing. I'm still hoping though!

Believe me, when I fix this I will let EVERYONE know.

 

[Dave 2000]

You should have OBD II on that car, no lights being shown on dashboard? O2 sensors often throw a code with the light when they go out of range, can you access a reader? Multimeter in this area is a bit hit and miss as the changes in temp can produce a fault and only at a certain time, you can bet it will not be when you are under there with a DMM!

regards

Dave

 

[nuclearlemon]

02 sensors should throw a code, but it may take a while before they do. i had the same symptoms one day, two days later, it was fine so i drove about 40 minutes away and all was fine. went to drive home and the issues came back. turned out the wires at the sensor itself were chafed.

 

[kidglove13]

His 93 is OBD I, get out the paper clip

 

[BlueCruiser84]

I guess an O2 sensor could make sense because occasionally, after it warms up a bit, it will suddenly start running right. It ALWAYS has the miss at cold startup and 1 out of 20 times it will go away when driving.

You should have OBD II on that car, no lights being shown on dashboard? O2 sensors often throw a code with the light when they go out of range, can you access a reader? Multimeter in this area is a bit hit and miss as the changes in temp can produce a fault and only at a certain time, you can bet it will not be when you are under there with a DMM!

regards

Dave

His 93 is OBD I, get out the paper clip

Yes, OBD 1 and no check engine light. It does turn on when I start the car and when I unplug various sensors so I know it works.

Will the diagnostic plug show a code if the light isn't on?

02 sensors should throw a code, but it may take a while before they do. i had the same symptoms one day, two days later, it was fine so i drove about 40 minutes away and all was fine. went to drive home and the issues came back. turned out the wires at the sensor itself were chafed.

When you say it was showing the same symptoms are you referring to the symptoms I described? If so that gives me hope!

 

[kidglove13]

Put a paper clip in the terminals and see if there is a code whether or not the CEL is on
It cant hurt
If the CEL is blinking really fast that means no code after you put the paper clip in

 

[Dave 2000]

His 93 is OBD I, get out the paper clip

Ooops I shot to the top of the page and read off 96, just looked again and this thread is on page two already and that ws aother posters car, sorry it was a blonde moment!

Er yep paper clip it is then my friend.

regards

Dave

 

[BlueCruiser84]

It's on page 3 actually

Did the paper clip and it was a constant fast blink. No codes....

EFI relay did nothing. It starts a bit quicker but nothing as far as the idle.

Tested the resistance on both O2 sensors and they were both within range. I couldn't test how many times they were pulsing because I need an analog volt meter. I'm headed to the beach for the next week so I guess it will have to wait.

Thanks for hanging with me fellers. I know we'll get it figured out. By that time it should be mostly new parts under the hood...

Brian

 

[kidglove13]

Just take your wallet out and throw it at the truck

 

[MyCrush]

I would think, based on my experience from the past, that perhaps the intake tube past the air cleaner to the engine might be worth a look. Couple of years ago, a dealership in the process of a servicing, checked my air cleaner<94> and in the process of opening the can, cracked the intake <which I believe aslo houses the MAF ?>. Caused me probs for 2 days till i figured it out.....might be worth a looksie.

HTH

 

[Funner]

X2 on the intake boot. It's likely pretty brittle and you may have cracked it when you took it apart.

 

[Dave 2000]

It's on page 3 actually

[Dave 2000] Hmmm the pages on my laptop show we are still on page 2?

EFI relay did nothing. It starts a bit quicker but nothing as far as the idle.

[Dave 2000] uhuh.

Tested the resistance on both O2 sensors and they were both within range. I couldn't test how many times they were pulsing because I need an analog volt meter. I'm headed to the beach for the next week so I guess it will have to wait.

[Dave 2000[ uhuh.

Get the compression tester out and as mentioned the air intake trunking could be split. Try sprayng a little WD40 around the trunking whilst the idle is bad, any change in engine note indicates it is pullling air in.

regards

Dave

 

[BlueCruiser84]

Ok. New weirdness is making me suspect something electrical alternator/bad grounds etc.

I had the computer down probing it with the multimeter with the key on for about 30 minutes. Go to start it after that and it tries to turn over, then just clicks. I go get a vehicle to jump it and hook it up negative to negative, positive to positive and it cranks over better than ever and.... it's running great! unhook cables and go for a drive. The dome light is flickering as well as the door ajar light on the dash. Runs great tghe whole time with only a tiiiinyy little skip in the idle every now and then. SWEET. Go home and park it for the night.

Start it up the next day after work and it is running s***ty. I say f**k it and go for a drive. Voltmeter typically reads at about where I would imagine 16 to be which seems high but I attributed it to the gauge. Turn on headlights and it drops. Use blinker and it is ticking with the blinker light. Hit brakes lights dim. Hit gas and lights get much brighter. Then it starts cutting back and forth between running sh*tty and running great... Drive home. Mutter a few choice words. Apologize. Go to bed mad at each other.

Before all of this started the PS reservoir was puking fluid into the alternator. Shortly after I repaired that I was getting the "christmas lights" on start-ups but that quit (I didn't do anything it just fixed itself) and hasn't come back since.

 

[bpenn1980]

Gawd I hate electrical troubleshooting.

The last time I noticed light dimming with turning on accessories, etc was when my battery retaining strap and a battery terminal connection were shaken loose in Death Valley. The alternator is a good place to start it sounds like. I havent rebuilt mine, but I'm sure there are some simple tests to see what output it is generating. I can check my 94 fsm if you want?

 

[4wdJOE]

FWIW on my nissan pickup it smelled like fuel out of the exhaust and putting in new 02 sensors fixed that right away .... i dont think thats gonna fix your miss fire though