91 k1500 sudden no start (fine last night)

[columnshift]

The 1991 K1500 chevy pickup 4x4, 5.7L v8, auto, 21k miles.

The one I recently got running (had to pay someone else to swap the fuel pump and idler... something... in the TBI, I dont have the sheet handy) all the sudden this morning wont start and i'm 250 miles from home having thought it would be okay now. >_
Ran perfect all previous night to get here 250 miles, and had a couple of start/stop cycles yesterday already around town once arriving. Last thing I did before driving home was to put gas in the tank about 15 gallons, ran fine home and shut off fine.

There's an exhaust leak in the muffler but not aware of anything else wrong. Has been starting fine in the cold so far/same temps as before.

All the sudden it just wants to crank and crank, when I play with the throttle (something I know I shouldn't have to do in TBI) it finally catches and runs rougher than crap only as long as i'm messing with the throttle. Soon as I drop the throttle it dies.

Obviously there's a long list of potential issues or problems and I don't even know whether i'm going to be able to do anything myself (limited tool access here/out of town/didn't think it was going to crap out) but just wondering where to start on the odd chance it's something random or explicable.

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EDIT: And now I go out there, and it starts up. So I shut down and it restarts several times. Except now I dont trust it and am wondering if I can rely on this to run or not.

Shorted the OBD1 pins and it's showing Codes 12 and 32. Yet it's seeming to start despite that.

 

[charbaby]

Well, I don't think it the gas you put in. I had this same issue right after filling up one time.
I fill up my tank, went to work(everything was fine). But when I was leaving work, I could barely get the engine started and the car ran like UnoWhat! Turns out, I had a pinched fuel line after all those years.

Start out by checking fuel pump pressure, coil spark, vacuum hose disconnected, wires chewed by rodents, pinched fuel line etc. Others will chime in with more!

 

[columnshift]

Is there any possibility that new gas stirred up "old gas tank crap"? (watched a scotty kilmer video on why to never let your gas tank run too low in an old car/buildup of old rust particles and what not start sloshing around... it's possible this what killed my fuel pump 5 years ago/I dont really know, cuz I let it get down to maybe 1/4 tank I dont even fully remember... this time it was... maybe 1/3 of a tank? 15 gals into what I think is a 23 gal)

All the sudden it's starting again and running okay. Started several times but I already missed my appointments for today because I don't know whats going on or if I can trust it. Codes 12 and 32 still showing but the check engine light is off when the engine starts up.

 

[charbaby]

Maybe! How old was the "old" gas?
I mean, any sediment should be caught by the strainer.

 

[The_Jeff]

Originally Posted by columnshift

EDIT: And now I go out there, and it starts up. So I shut down and it restarts several times. Except now I dont trust it and am wondering if I can rely on this to run or not.

Shorted the OBD1 pins and it's showing Codes 12 and 32. Yet it's seeming to start despite that.


So with 32 being EGR it certainly could be stuck open. If you're trying to get home, take the valve off and put a slice of soda can under its pintle. Or, since you assume it is now closed, disconnect its vacuum source. It is certainly plausible that the valve is sticky after resting a while or if it was in a truck that short tripped a lot. You can even take it off and poke its pintle with a pencil, hose it out with brake cleaner etc to free it up, or, if you can reach under the vacuum "mushroom", activate it that way to see how scratchy it feels. Might work itself out.

EGR will give you a lousy idle but drive okay down the road. I would not be afraid of being stranded on the interstate with an EGR stuck open, though it will make you run like a cammed out lobsterboat around town due to the low vacuum (via leak) at idle.

If it doesn't have an EGR sensor it might infer that with its MAP, which is central to how the injection runs. If it starts acting up again I'd unplug various sensors to try to trigger a fail-safe that runs better.

 

[CT8]

"All the sudden it just wants to crank and crank, when I play with the throttle (something I know I shouldn't have to do in TBI) it finally catches and runs rougher than crap only as long as i'm messing with the throttle. Soon as I drop the throttle it dies".

 

[Linctex]

Bad fuel filter..... bad fuel pressure regulator.... bad ignition coil

 

[CT8]

IAC motor?

 

[DoubleWasp]

Use of a multi meter can test all of the sensors and such in short order. I've gotten good enough I can test everything in just a few minutes.

TBIs can also do this weird thing where they air choke or something. I've gotten them to run by cracking the fuel fittings (like restoring prime to a diesel) and cycling the fuel pump.

Take the air cleaner off when it does it again and have someone crank to see if you are getting fuel. Use a noid light to check for injector pulse. Confirming pulse eliminates a lot of possibilities, and showing none narrows it down.

You can get an OK noid light set and MM for about $35. I have a link for the full sensor test flow chart if you need it.

 

[dogememe]

Replace coolant temp sensor. The one for the computer, its 2 prong, not the one for the gauge.

 

[andyd]

1991 K1500 chevy pickup 4x4, 5.7L v8, auto, 21k miles More yrs than Kmiles is gonna be the problem with this truck. I recommend a total refit of the tank and associated plumbing. At least inspecting the the heck out of it. A bad load of fuel? Just as likely is a bad electrical connection or a bad new fuel pump?On old BMWs, most electrical gremlins disappeared after replacing the fuses and some contact cleaner. I wouldn't condemn a part until I cleaned up the connections to it. Also spend some time time checking out the brake lines. Only exception to testing is to replace the CTS just cuz.

 

[dogememe]

Originally Posted by andyd
1991 K1500 chevy pickup 4x4, 5.7L v8, auto, 21k miles More yrs than Kmiles is gonna be the problem with this truck. I recommend a total refit of the tank and associated plumbing. At least inspecting the the heck out of it. A bad load of fuel? Just as likely is a bad electrical connection or a bad new fuel pump?On old BMWs, most electrical gremlins disappeared after replacing the fuses and some contact cleaner. I wouldn't condemn a part until I cleaned up the connections to it. Also spend some time time checking out the brake lines. Only exception to testing is to replace the CTS just cuz.

Yeah for $16 at any parts store the coolant temp sensor is a no brainer.

 

[Rhymingmechanic]

Code 12 is just a place holder. It will flash if no trouble codes are stored, and it repeats in between codes or after all codes are done. It's been awhile since I had an OBD 1, so I can't remember which.

Code 32 is for EGR, but I don't know if it would cause your problem. I did have a replacement EGR valve start sticking open slightly on a Saturn, and it caused it to idle a little rougher and "fall off" too much between gears.

Good luck.

 

[The_Jeff]

Code 12 is an "instant" code, eg, it doesn't stick around.

It reads "computer is not seeing spark impulses" which is a fancy way of saying the motor's not turning, at present.

If you somehow had a carburetor and distributor smart enough to run without a computer, you could plausibly run with an active code 12.

 

[columnshift]

Originally Posted by Char Baby
Maybe! How old was the "old" gas?
I mean, any sediment should be caught by the strainer.


It was verging on 5 years, i'd put PRI-G periodically in there to keep it startable and that stuff seems to both keep the gas startable and reduce varnishing, but i'm aware that even if i'd been regularily refilling the tank and burning thru it whatever is in the tank if there's any rust particles or something will eventually end up in the filter... #1 these tanks slosh unbelievably (with 1/3 of a tank when I do even just a moderate stop i'll see the fuel gauge swing all the way from the E to 3/4 full) and #2 the sediment in any constantly refilled and emptied container is just gonna keep building up and since the truck has been so little driven since new I know it hasn't been replaced - that's 30 years of potential internal rust or sediment. At ~21k miles thats only I dunno, 65 lifetime tank refills or something? I tried to generally keep the tank full while parked (i'm told it's worse to have it empty) but I don't rule out rust being in there, tho i'm not sure how to verify without a long inspection camera or something.


Originally Posted by andyd
1991 K1500 chevy pickup 4x4, 5.7L v8, auto, 21k miles More yrs than Kmiles is gonna be the problem with this truck.


Oh I agree. It has so few miles because it was my dad's baby, it barely ever saw rain or snow for 15 years - it might sound cliche or corny but he'd just drive it to church any dry sunday or about once per month in the snowed winter to not let it sit when they'd just cleaned the streets and refused to let anyone else drive it. Problem is I had to park it outside a few years after I inherited it because of other junk in the garage and when it gave me the fuel pump problem 5 years ago I just didn't need something getting 11mpg around town so it stayed parked while I drove something else.

The problem right now is it's the only running vehicle I have to try and get through the winter, and I got medical advice to stay out of the cold and so it's all a game of minimizing or postponing other refit expenses FOR NOW to try and last until next summer, when hopefully it's not my only transportation, and where if it's up on jackstands awhile I don't need it running the next day and it can sit until everything is made good again.


Originally Posted by andyd

I recommend a total refit of the tank and associated plumbing. At least inspecting the the heck out of it. A bad load of fuel? Just as likely is a bad electrical connection or a bad new fuel pump?


Refit meaning flushing it out somehow? I assume it'd have to be pulled back off the vehicle to do that... And what other plumbing to refit/what would you recommend changing and inspecting? Not trying to be dense i'm just not a mechanic and i'm still learning how and what to do as I go.

Though alot is just going on a future to do list. Most of the more involved work will have to wait until summer when I can hopefully catch up on all deferrable maintenance.


Originally Posted by Rhymingmechanic
Code 12 is just a place holder. It will flash if no trouble codes are stored, and it repeats in between codes or after all codes are done. It's been awhile since I had an OBD 1, so I can't remember which.

Code 32 is for EGR, but I don't know if it would cause your problem.


Well i'll bring everyone back up to speed on the last 72 hours.


The truck has actually been throwing a code for a month but since whenever it did, how it ran didn't affect it at all, I assumed it was just something like the catalyst not being as efficient. I had a muffler leak too so figured the lack of backpressure was probably throwing things slightly off emissions wise, plus the code would go off again before the next drive, so like a fool didn't even bother to check the code/was so busy with other crises of the moment that it didn't seem dire. The 'check engine' would periodically come on during highway driving only when it was running for awhile, not shorter term city driving so I wasn't too worried yet I guess.

I took it on an out of town run during which it ran perfectly fine all the way down and through a few restarts. Then in the morning I turned the key and it gave me the 'no start' out of the blue. Tried multiple times and no dice.

One time I got it to fire while playing with the throttle, but it ran horrible, and when I dropped the accel it died again and I smelled gas so it was probably too rich.

Let it sit several hours, went out and turned key - started fine like it had never done that out of the blue problem. I said huh. Ran a brief around town errand 10 miles one way, shut down, restart no problems, 10 miles back, shut down, fine for that. I finally remember I can check OBD codes by shorting the two upper right pins and it gives me the 12/32 combo.

Half hour later I come out, try to restart, and this time it throws a rapidly flashing check engine light, it's running but it sounds a little rougher. I decide i'm not sure whether it will or wont start up again next so this time I just let it run - the rapid flashing turns to a slow constant flashing (before it was constant on) but I load my crap up and decide to limp the truck back home cuz I have no tools to work on it where I was and similar anyways and with a pending blizzard I dont want to mess with so I drive 65mph home 200 miles - slow flashing check engine the whole way - too afraid to shut it off or stop just figure set cruise at constant load, just get me home and i'll sort it out there. Got home fine.

One thing i'm a little confused by is the difference between the rapid flashing, slow flashing, and constant on codes - including the last where sometimes it would go on and then go right back off again incl after every restart. Thats why I wasn't too concerned cuz the code would go back off again and never be there on restart for around town drives. It'd only come back with like 10 miles of highway drive.

 

[mk378]

OBD1 systems don't have a lot of codes; when one is set it almost always means a serious driveability or reliability problem is coming.

 

[The_Jeff]

https://www.chevytalk.org/fusionbb/showtopic.php?tid/247009/

Are you sure you didn't have the OBD connector shorted when you ran it? There's a "field test" mode where you stick a wire (or a resistor) and then it indictes rich/lean by the blinking CEL.

But the above thread thinks the computer is pooched. Which is possible, capacitors dry out and the computers were never that great to begin with.

 

[WyrTwister]

The previous talk about rust / debris in the gas tank , if you are concerned , replace the fuel filter .

We have a 1991 Caprice 5.0l which I have replaced the fuel pump / strainer & external fuel filter . The filter was not that bad to do . Do not know how similar your vehicle is to our Caprice ?

Another thing I discovered , our Caprice has a " pigtail " by the fuel pump relay . You can connect 12 VDC positive to that " pigtail " and force the pump to run . Might try this next time it fails yo start .

I think , how it is suppose to work is , you turn the key on and the pump comes on for a few seconds . There is an oil pressure sensor . When it senses good oil pressure , it activates the fuel pump . In theory , you start cranking the engine & by the time timer times out , the sensor sensed positive oil pressure & keeps the fuel pump running as long as there is good oil pressure . I wonder if there may be a problem with the sensor . If your vehicle is wired that way .

I have heard a stopped up oil filter will cause the sensor to turn off the fuel pump ?

Best of luck to you ,