86 GMC engine question

[68Stepbed]

OK. The engine in my 86 is acting up a little. It deisels or pings alot when under a load. I'm pretty sure my problem is mostly in the smog equipment. The truck only has 48,000 miles, but the PO only drove 7 miles at a time, which isn't enough to clean out any carbon. It probably did more harm than good. The truck ran great for the first 2 months or so, but seems to be getting worse everyday.

My questions are: Is my engine computer controlled? It has an electronic carb, but there is no oxygen sensor.

Can I remove my smog equipment, install a new intake, carb, dizzy, and exhaust and still work well with the stock cam?

The laws will not effect me here.

Please help me. I don't want to spend a small fortune replacing outdated smog equipment.

[magnethead]

what octane fuel you running? is it a 305 350 or 454? Run the engine up at at moderately high RPM and trickle ATF in the carb- it was suggested to me (didn't do it) because it cleans out the combustion chamber.

[89 crew]

You will have an ecm.. if the emisions won't bother you I would rip that crap off! actually I have! An old hei and an eldobrock carb will work wonders for you. If you want to fix what you have find the anti knock sensor check the wires first(they usually get cooked by a manifold) If they are on then replace the sensor. I am assuming that your truck is running the Electronic spark control. When I removed it from an 80 half ton it gave me 3 mpg and it ran a whole lot better!

[68Stepbed]

It's a 305. That's why I don't want to sink too much $$ in it. If I'm gonna spend any $ on it, it needs to be something I can use on a 350 later if something happens to the 305. I only run Exxon 93 octane in it. Gettin over 18 mpg now, which is what's so weird. It gets better mpg than when I first got it and actually runs better, but it pings under a load. It also seems to run good on just the primaries, but if I have to open the secondaries to pass someone or jump into heavy traffic, it's like it really strains to run and deisels real bad.

Is the cam in this engine setup for the Elec. Spark Control, or is it just a standard hyd. flat tappet? My mechanic said if it was a computer controlled cam, it would never run right if I changed carb and ignition. He's seen too many people try it unsuccessfully. The problem in his explanation is that I've seen and heard everyone that has done this to one of these types of trucks hasn't had the first problem. I have heard of problems like this in some of the cars like Monte Carlos and Caprices with the more complicated ECM setups.

So what do I do?

[85 K5]

The electronic control module for the spark uses the knock sensor to retard spark when knock is detected. Eliminate this and eliminate problems it may cause, it is not necessary. From the distributor you will find a harness that goes through the firewall near the ac box, passenger side. Between the firewall and distributor is a connector. On the distributor side short pins 1 and 3. (jumper wire) This effectively disables the ecm completely and the knock sensor is does nothing.
Next is not as easy. The knocking is probably caused by poor fuel delivery and the egr ports. You will need to rebuild the carburetor. The original qjet you have is in my opinion one of the best. However of the shaft is leaking it will need to have bushings replaced. I found someone in my area who knows carbs through and through. He rebushed the shafts, enlarged some of the orifices for better air and fuel flow, really brought the 350 to life.
Another problem you most likely have is plugged ports for egr flow in the intake manifold. During idle if you disconnect the vacuum line to the egr you should notice a considerable difference in engine speed. if you do not then the intake must be removed and cleaned. There are passages inside that cannot be effectively cleaned without removal of the intake. I would suggest getting an aluminum such as Edelbrock performer or performer rpm. You can swap this to your 350 when you get it. Get one without the egr and eliminate problems it can cause as well. Another option is an egr block off plate - simply a plate that covers up the ports where the egr mounts to the intake. Either way you will now have to adjust timing for best performance and no knock under load. 7 - 12 degrees btdc. I know this is more than you had hoped to do but most is necessary - been there, done that.
Good Luck!

[Slonaker]

The 305 in my '86 never had any problems running on 87 octane gas. Yours should be able to as well.

You do not have a computer or an electronic carb. The wire going to it is just for the accellerator pump.

Mine had most of the emission controls removed, and it ran just fine. I would definitely try the distributor fix 85 K5 talked about. I have talked to a couple of people who tried it and they were ver happy with the outcome. More on that here (at the bottom of the page):

http://www.73-87.com/7387garage/drivetrain/escrepl.htm

Slonaker

[86swb]

I think you are just wasting your money on the higher octan gas. 87 is all you need. That is all I use and mine runs great. I also took all the smog stuff and install an Edelbrock and carberator and runs mush better than with all that smog crap on it. But I know some states do require you to leave it on but not Kentucky.

[magnethead]

I even run 87 in my 454 and it only pings when you throw a good sized load on the hitch, and 89 fixes that problem

[68Stepbed]

OK, I unhooked the vac. line to the EGR valve, no change in idle. So I guess I need to go buy an intake and carb. No smog laws here in TN. I ran a tank of 87 octane a couple weeks after I got the truck. It barely idled, pinged really bad, and barely lasted three days. I can run a week on a tank of 93. Maybe after I remove the smog equipment I can go back to 87 or 89.

My heat riser valve is also acting up. Would this cause a problem?

[Slonaker]

You can just block off the EGR if you don't want to replace the valve. I cut a blockoff plate out of steel using the EGR spacer as a template, then put the plate over the hole with the spacer on top to strengthen it. It has been that way for 6 months with no problems so far.

BTW, according to my friend the GM mechanic, the EGR valve helps prevent pinging. You might want to try keeping it.

Slonaker

[1972C10]

Have you checked the Timing? And With A Light?

[68Stepbed]

I talked to a guy yesterday that told me to run some Top Engine Cleaner from GM through it. Tried it and really seemed to help alot. This stuff cleans out alot of the carbon build up in the combustion chamber. It blew out black smoke, then blue, then gray, then white, then blue smoke again, stunk real bad, choked, spit and sputtered alot.When it finally smoothed back out, I drove it around. It ran alot better. The biggest part of the problem may have just carbon buildup.

[86swb]

What is this "Top Engine Cleaner" from GM called?

[SSC's76]

The top end cleaner is good stuff. I use the JB treatment systems at work, cost less but have more components and better results. Most likely it is a stuck EGR valve or a blocked off passage. I reccomend you, remove the EGR and see if theres any carbon build up behind it. If there is start the engine with the EGR off and dig out as much as you can with a pick or small screw driver. Wear goggles when you do this because once it clears the crap out the carbon will start shooting toward you. The fuel grade you are currently running is way overkill. These little 305's they stuck in most trucks depending on your check digit are nearly all 8.5:1. You can dang near run kerosine with that compression ratio.

[piecesparts]

The top engine cleaner is basicallly a mix of tranny fluid and brake fluid. This stuff will clean out carbon on a seriously carboned up engine. It would be a good thing to get the top end of the engine cleaned out. If you decide to take the stuff off of the 305 and upgrade, I would look at a couple of things. First I would get an older HEI distributor, to eliminate the computer feed to the timing circuit. Second, I would get rid of the factory intake and get something that has a little rise in the flow chamber (Edelbrock makes a good one in their dual plane intake). Then I would look at a decent 600 to 650 CFM carb for your engine to get the system going. You really do not want to go bigger than that on a daily driver, that weighs as much as a truck does. Anything above the 650 CFM will over carburate the motor and cause you to have a poor acceleration capability in city driving. (Sloppy, doggy acceleration) Another thing to consider is a new air cleaner and get the motor breathing better. I am using 14" X 4" K&N air filters in my vehicles for ease of use. After installing the intake, carb and distributor, then look at setting the timing at about 12 to 15 degrees initial timing and look at what your TOTAL advance numbers are. I actually set my motors to a total advance around 34 to 36 degrees and I have no problems with my trucks. I would also look at putting a advance kit in the HEI distributor, to get the timing to advance quicker on acceleration. NOW, your motor is set up on a basic design of an older motor, that has only spark, fuel and air. All of this will move over to a GM 350 motor,so your money is not wasted on this engine.
What do you have for an exhaust system? If you have good air and fuel going in, then you want to get the exhaust out.

[86swb]

Is the EGR the thing that is in the valve cover with the hose? I know very little about these engins. Tranny fluid and brake fluid? Who would have thinked it? I just would not feel good putting tranny fluid and brake fluid into the engine. But if it works and does not harm the engine-well-I guess.

[piecesparts]

The EGR is the flying saucer looking thing that is sitting beside the Carb on the passenger side of the intake manifold. It has a vacuum hose that runs to it and usually is light in color. This thing allows exhaust gases to return to the intake to ensure that there is a more complete combustion of the incoming gasoline charged air in the motor. If it is stuck in a slightly open condition, then it is going to cause some air/fuel mixture problems and that could be part of your trouble. The stuff in the valve cover is the PCV valve on one side, which goes to the base of the carb and on the other side is just a connection for a controlled air source to the engine. The design here, is to let air into the engine and pull ithrough the crankcase to the PCV valve and then into the intake to burn up any oil vapors that are given off from daily use.

As for the engine upper end cleaner--you pour gasoline down the carb everytime you start the vehicle. The gasoline is something that can clean and cut grease and dirt away, just like any other chemical. The Tranny fluid/brake fluid type cleaner is a little tougher on carbon and dirt. The principal is to soak into carbon and cause it to break loose from the valves, pistons and cylinder heads. Once you get this stuff to soak into the hard carbon, then you start the engine up and run it to clean the carbon out the exhaust. This causes a lot of smoke for a short period and as stated above, a lot of grit is sent out also.

[68Stepbed]

piecesparts, thanks for the info. That is exactly my plan except for the carb. I was planning on a 500 cfm Edelbrock. I can still swap the 500 to a stock 350 and it won't be overkill on the 305. I've seen too much trouble from 600 and650 carbs on 305's. It seems to be running good since the engine cleaner, so I'll see how things go with what I have for now.

-EDIT- For the exhaust, I would plan on using better flowing manifolds(similar to what late model EFI engines use), no cat. conv., and either true dual 2 1/4" pipes with 50 series Flowmasters or using a Y collector, run 2 1/4" pipes into one 3 inch exhaust with a single 50 series Flowmaster.

[piecesparts]

OK It's your thing, but the 600 CFM will work quite well on the 305 and smooth out more on the 350. These engines respond extremely well to a set of long tube headers (cyclone, hooker, etc...) and true 2 1/2" dual exhaust pipes with Flowmasters. I have two trucks around here that are set up that way and they run great. Both trucks started out as 305 trucks and one is now a 350 and the other is a 383 stroker motor.

[68Stepbed]

OK, the truck was runnin pretty good since I ran the engine cleaner through it, so I figured I'd see how it did with some 89 octane fuel. Two words: BAD IDEA! It pings so bad it almost knocks now. This is under normal driving too. I still have a full tank of this crap. Would octane booster help?