Hot Rod Forum banner

1 - 13 of 13 Posts

·
Registered
Joined
·
71 Posts
Discussion Starter #1
A friend came to visit in his 1986 Chevy with the 4.3L V6 TBI injected car with twice around on the clock. It ran fine when he arrived. When he left, he returned a few minutes later because the car was bogging down on the slightest gas, shaking, and occasionally bucking with a light backfire.

I went for a test drive and it acted like another vehicle I once had when the ignition system in that car was running on the "start" reluctor because the "run" reluctor or pickup had gone open circuit. The engine would cough, bog or backfire if gas was applied at low rpm or under load. It ran better at higher rpm but not great. It picks up rpm slowly once spinning fast enough to get past the bogging and sputtering. Even then, more throttle or load caused protest from the engine.

We looked around and no vacuum lines were loose. Vacuum measured 20 at idle and steady. I didn't see any timing marks on the flywheel to check the timing and it was dark, cold and time for him to leave anyway.

We have no documentation for this car... so no idea about the ignition system except that it is obd1 computerized with two thottle body injectors. Wires look okay. Cap looks okay to. Are there two timing pickups, one for run and one for start in this car? It acts like the timing is way late. Any other ideas what to check?
 

·
Registered
Joined
·
245 Posts
any number of things can cause the problems you are having. a plugged gas filter, egr valve, spark plugs etc . did the check engine light come on.
 

·
Registered
Joined
·
71 Posts
Discussion Starter #4
It happened quite suddenly. He drove here and it was fine. He went to leave and it was broken. The difference was quite obvious with the car just about undrivable when he left.

EGR circuit was cleaned up last year and the valve operating smoothly. It didn't run this poorly when the egr passages were clogged up. They are open now.

I think most of these other things would degrade gradually, such as fuel filters, plugs etc. It passed emissions with good margin last year too, so I don't think it is degradation. I'm thinking it is an outright failure.

The check engine lamp didn't come on. The engine computer is pretty basic in terms of diagnostics though. I think it can alert an egr or map sensor issue if it's flat broken but not much more than that.
 

·
Registered
Joined
·
1 Posts
Problem Fixed

I would bet you anything that the ignition pickup coil is the problem. I drive a 1992 chevy pickup and it did the same thing. Try the pickup coil it costs about 14 bucks so what do you got to lose.
 

·
Not Considered a Senior Member
Joined
·
10,722 Posts
I agree it`s in the ignition system somewhere, I worked on a car last year that did this same thing. see if you can disconnect the computer control to the distributor and it run okay, if so you`ll know it`s in the ignition.
 

·
Premium Member
Joined
·
2,370 Posts
Grab a book for it and run through the fuel pump relay and fuel pump tests. Pop the hood and have one guy under there. Have the other turn the key to the ignition on and you should hear the fuel pump prime. Do a fuel pressure test as well. Out of spec fuel pressure can cause symptoms like you describe.

Like has been said its also possible your timing control unit is freaking out causing this problem. Be careful about having it disconnected too long. You will undoubtably run rich and things might start to glow (my headers glow after awhile of running with my EST disconnected on my TPI).

Also unplug the MAF and see if it makes a difference. It shoudln't even really start without it plugged in. Do the tap test as well. Tap on the MAF with a screwdriver while its running. See if any reaction occurs.
 

·
Registered
Joined
·
288 Posts
Didn't think they had the 4.3's in '86. I know that had 3.4's... what kind of car is it? I'm probably wrong, just haven't heard of it
 

·
Registered
Joined
·
64 Posts
we should change the sites name to shadetreemachanic.com. oh wait that right, there is a site with that name. this is hotrodders. or sometimes it tries to be. sometimes it tries to hard and becomes XtrEEm_racer.com. i m printing your question out . then wiping my *** with it.
 

·
Licenced Automotive Technician
Joined
·
1,625 Posts
we should change the sites name to shadetreemachanic.com. oh wait that right, there is a site with that name. this is hotrodders. or sometimes it tries to be. sometimes it tries to hard and becomes XtrEEm_racer.com. i m printing your question out . then wiping my *** with it.

I don't understand why some here get so upset over questions like this one. Sure, this is a hotrodding site, but all this stuff, like why does it bog or backfire, is the very basic stuff of hotrodding. If we get abusive to this type of question, we could say screw the basics, ya don't need 'em. Even if the post isn't initiated by someone building a hotrod, the pricipals discussed may help solve problems for those of us that are, not to mention help the guy asking. After all, most of us here don't mind helping others out, in essence, that's what we're here for. Replys like yours make us all look like a$$holes.
 

·
Premium Member
Joined
·
2,370 Posts
Cant very well work on our hotrods if our parts getters aren't getting us all the way to the parts store.
 

·
Registered
Joined
·
71 Posts
Discussion Starter #13
Spankynutz,

Kiss my grits. I'll go to ricers.com when I need a reply like your's. I'm sure I'll find you there.

To the other very helpful replies, I very much appreciate the suggestions and answers. BOBCRMAN wins the prize. I believe there was water in one of the two injectors. With the next longer drive (the car is driven infrequently) the problem was gone and never returned. It behaved very much as though the timing was retarded or chain slipped. I was concerned that there might be a nylon timing gear issue.

KNanthrup, there were some 4.3L V6 Caprice (Impala) made in 1986. It was somewhat underpowered for a car this size but it was good on gas. The car gets 21MPG on the highway which is not bad for a car that size and age. It always ran smooooth and started without protest.
 
1 - 13 of 13 Posts
Top