Head Gasket?

[5th]

Hi folks, about to spend alot of time googling and thought I'd start here.

Was out for a drive yesterday, noticed the motor would drop off at 80kph as if I had taken my foot off the pedal. Got it up to 90kph and the problem seemed to have corrected itself.

Went for a drive today, about 2 hours. (I always baby my baby, no hard wheelin' or burnouts)
Shut her off, went in the store, came out. Started it up n' she ran at full idle.

With my 86' sub I knew about the choke, give it a solid shot of fuel and it would start to idle normally. So I tried that and it didn't work. Figured since this sub is a 91' with the TBI maybe it doesn't have the same choke shut off.

Got about a block from the store and the engine stopped as if it had run out of gas.

Had to hold the pedal to the floor to get her started again. When it started I got a big plume of black/grey smoke out of the exhaust.

Pulled over and it died on me again.

Checked the antifreeze, no discoloration. Oil was only about half full, which was odd.

Checked the tail pipe and the inside is coated with oil. (would explain the black smoke)

So head gasket? Did I just get lucky enough to catch it in time?

 

[yevgenievich]

black smoke would indicate excessive fuel. Check the fueling before moving to more expensive possibilities. Take air cleaner off and then watch the injector pod while having someone turn ignition to on position. Fuel pump will start running and if there are fuel leaks it will shop up. Next would be to try to run and watch the injectors.

 

[1987 GMC Jimmy]

Is there any oil in the air cleaner/air filter? I'd replace your PCV valve just for kicks, too. Yevgenievich is right, though. You do need to look at fueling first. If you do find something wrong with that, awesome. If not, there is a chemical test you can do to see if exhaust gases are getting into the cooling system. If coolant is getting in the oil, you'd see oil that gets milky and a white froth on your oil cap. I'd smell your oil and look at how viscous it is, too. If it's watery and strongly gas-smelling, that's another clue for a potential fueling problem. I'm sure you'd know about a leaking rear main seal, oil pan seal, oil plug seal, dipstick tube seal/grommet, valve cover gasket, etc., but is there any light blue smoke at startup? That would indicate bad valve seals more than likely, especially on the exhaust valves. Either way, it sounds like you're loosing some oil, and oil in the tailpipe makes me think valve seals. Once you fix the problem and looking down the road, I'd consider cleaning, removing, gutting, or replacing your catalytic converter with the intermediate option being my preference in an emissions exempt world. I know that's very big picture, but I'm just trying to think of everything.

 

[5th]

Thanks for the fast reply's guys.

The air filter was replaced 1000 miles ago when I did the oil change. Just popped the cover and it looks clean n' new.

All gaskets/seals are accounted for n' in fair to good condition.

No blue smoke. Just white while turning the motor over, then turns dark/black.

It gets to that stage when you know its about to catch n' fire up but falls just short of running. There is smell of fuel coming from the tailpipe however.

Popped the oil cap n' it was clean oil, turned the motor over n' it still looks like new oil. (clean/viscous)

It's unlikely I got a bad batch of gas but i'm not ruling it out obviously. Gonna be a nightmare dropping the fuel tank on this thing.

 

[5th]

Checked all fluid levels, everything was fine.

Took the air filter off to watch for any abnormality with the throttle body. My assistant turned the motor over for me and the truck fired up right away, the way it always has.

No discolored exhaust, normal idle speed.

Let it run for 20 minutes at idle, noticed the 'check engine' light was now on.

Went out two hours ago. Started again no problem. Figured I'd take it for a quick drive to burn out any excess oil from the exhaust pipe....

Terrible idea. I made it about 6 blocks before it coughed sputtered n' died.

2 tow trucks in 24 hours...not my idea of a good time.

 

[crazy4offroad]

Definitely doesn't sound like a head gasket, more like a sensor. Reset the ECU and see if it straightens out but don't take it for a ride. Pull the codes if you can. Just a guess but sounds like what happens when an o2 sensor goes out of spec or catalytic converter gets stopped up.

 

[5th]

I agree with ya crazy4, if it was the head gasket it would be more messed up then it already is.

I was just thinking worse case scenario with the HG I reckon'. I panic quick when my daily driver doesn't run proper. ...besides, seeing a square not running is always a sad thing to see.

I replaced the PCV, which was a great suggestion.

It's definitely a fuel problem though, it runs rough and smells like I'm standing at a gas station. Even though I'm not leaking. Was standing in the exhaust and my jacket reeked of fresh gas for hours afterwards.

The new motor only has about 3500 miles on it, but the throttle body seems to be original. Might be the issue.

Any recommendations for a code reader guys?

 

[1987 GMC Jimmy]

A few suggestions here. As far as a code reader goes, you can use a paperclip to flash the codes by jumping pins A and B (two top right pins) or make your own scan tool that serves as an interface between your OBD1 ECM and a laptop using dirt cheap parts and public domain software. I'll attach a great thread that's on here that tells you how to do it. I would check your EVAP canister. Make sure the vacuum line is connected on both ends and solid throughout the length of it. Does the gas pump ever click off prematurely? That could be the sign of an EVAP canister problem. You could take it a step further by capping the EVAP port on the TBI and seeing if it does better. Moving on, if you're a believer in preventative maintenance, it may be a good idea to replace your coolant temperature sensor unless it's new. Those seem to degrade over time. Moving to the TBI, have you had a chance to watch the spray pattern on it? That's a good visual diagnostic, and if the injectors spray sloppily with good fuel pressure and good injector assembly parts, there are places that offer an electrolytic cleaning service on the cheap (i.e. WitchHunter Performance). Also, is there play in the throttle shaft in all directions? If so, it may be a good idea to get a bushing put in there because you're leaking vacuum if there's play. I used SPR Performance in Jacksonville, IL to do the one in my Jimmy for fifty bucks. If you send the base off, you can rebuild the injector assembly yourself for around $35. I hope that PCV helps with the oil. You said no blue tinged smoke at startup, but it's curious to me about the oil in the tailpipe which sounds to me like failing valve seals.
http://www.gmsquarebody.com/forum/showthread.php?t=13194

 

[yevgenievich]

Coolant temp sensor is definately worth checking. Tbi will dump a lot of fuel in if it thinks engine is close to 0* in temp, while it really is around 80*

 

[5th]

Have I told you guys how awesome you are yet today?

The EVAP system checks out so far. All lines are in good condition, even the connector rubbers are in solid shape.


I started to read the link, but got lost at the *bng, *idk, *wtf, files. It is at the top of my bookmark list however. I'm huge on preventative maintenance, (if you've ever owned a mid 80's Mack its the only way to keep 'em on the road) I'm also an avid DIY'er so its bookmarked under my "required reading" folder.

I've owned a CUCV, 3 sub's, and a halfton. ...and have never heard of the paperclip trick....

....but now I know flashy lights can be a good thing.

14- coolant sensor or circuit/ high temp indicated

44- oxygen sensor or circuit - lean exhaust detected

Thanks alot for taking your time to help me with this. Parts have been ordered, I'll post back after everything is installed.

 

[crazy4offroad]

Wish I would have caught you sooner, before ordering anything. You might want to pick up one of those Haynes manuals for these trucks, and an affordable auto-ranging multimeter. They will have voltage/amp/ohm specs for these sensors and the wiring that connects to them. Wiring can get pinched/broken and cause these codes to be thrown. Hopefully if you ordered those 2 parts they fix the problem but don't be surprised of they point to some other issue.

 

[5th]

If they fix the problem that's great, but I'm not holding my breath.

I just went through a month long debacle getting my speedo working. Turns out I didn't need anything but the screw in sensor for the t-case to make it work proper. It fixed a few other problems (slipping tranny/etc) as well.

First thing I check is the wire/line/hose connection/condition on any problem I have. ...just makes life easier when the simple things are out of the equation.

She is a 26 yr old truck, n' I'd like to keep her for another 26. So $70 for new sensors is a pretty cheap investment in my eyes.

I've had some gift cards since x-mas burnin' a hole in my wallet. I'll find a Chilton/Haynes manual n' a multimeter this evening.

 

[5th]

Haynes manual isn't in yet but other things were. Fancy multimeter thingamabob, just gotta read up on how to use it properly.

The squeaking under the hood was driving me bat**** crazy so I bought a new belt. That fixed it for about an hour. Decided it was time to replace some things.

Tension pulley was out of stock so I bought a new alternator. Still didn't fix the squeal.

Why the hell they put a new motor in this thing and bolted all the old stuff back on to it I'll never know.
Temp sender was a quick in n' out. Getting whats left of the O2 sensor cut out of the bung on Thursday.

Checked the codes n' I'm getting,

13- 02 sensor or circuit (understandable, nothings plugged in)

15- coolant sensor or circuit/ low temp indicated (upgraded from a 14 to a 15 it seems)

44- oxygen sensor or circuit - lean exhaust detected



I'll check codes again after the new O2 sensor gets screwed in. Then play with the multimeter in the coolant temp sensor wires.

 

[1987 GMC Jimmy]

Make sure you unplug the battery when you get ready to try it out to reset your ECM.

 

[PrairieDrifter]

Yeah if you had to hold the pedal to the floor to get it started back up it was definitely flooded with a bunch of gas. Coolant is usually pretty thick white smoke and smells kind of sweet.