Follow up on runs like crap and Backfires
 

Okay Guys and John Walker if you're out there,

Here's the latest on my situation. I pulled the valve cover off yesterday and checked the rocker arm on number #1 cylinder. Everything appears ok, no breaks loose springs etc. and works when engine is turned over. I also pulled the sparkplug and again it's wet with fuel. I did a compression check on cylinder # 1 this am before work and it reads 125 lbs. That's completely cold as the car won't run long enough to heat it up and the engine still hasn't been broken in and rings probably aren't seated yet. I only had time to do the one cylinder so I don't have anything to compare it to on the rest of the engine but I do have compression.

Now with all that said anyone got any ideas about why it's firing, for lack of a better description, in the intake and barely running? clogged and constantly leaking fuel injector? Bad or out of adjustment reference sensor or speed sensor, Stupid owner?

Dan O
84 3.2

so did you check the valve clearance on #1 intake while you were in there? all you need to do is put the engine on #1 cyl TDC position and rock the rocker back and forth to feel if there's any clearance. 125# is kind of poor for a 3.2, even cold. they pump 180 hot.

Re: Follow up on runs like crap and Backfires
 

But did you check the valve clearance???? Dan you realy have to work on this in a methodical manner. It really does sound like a tight intake valve problem.

Hello, don't you hate when people come in, somewhere in the middle?

Engine not broke in? Just rebuilt? Won't run long enough to get warm?

Distributor was installed by someone other than you?

Start from the very beginning as if you just got the motor back, time it from the very beginning, from someone whom didn't see your first posts I think a timing problem.

In the raw sense of it all, you need fuel, spark and air for combustion, your backfire means you have all three, just make it happen at the right TIME.......

good luck...Peter

P.S. if this is way far off base, I apoligize for butting in

John,

Yes, there seemed to be play at TDC although I didn't measure the gap yet. I pulled the compression test quickly this am and only cranked it over a couple times as I didn't want to damage anything anymore than it might already be. The compression tester I used has the soft flexible hose and I twisted it tight but not too tight as I was just quickly checking to see if I had compression. I'm not making excuses here I'm just relaying info. The engine was just rebuilt and I don't even have 5 hours on the engine yet so I don't know if that would account for low compression or the fact that I rushed through the compression test just to see if I had compression. I'm planning on pulling another one tonight. Any thoughts about the fact that I keep getting gas soaked plug in that cylinder?

As far as being methodical Kurt I thought that's what I was doing here. I will be checking the valve clearance this evening. As for an intake valve that's too tight I don't know. It was fine last week before the backfire so I'm not so sure it would just jump into being too tight although I suppose anythings possible.

Peter,

Not a problem jumping in here that's why people post is to get feedback. Yes the engine has been rebuilt and was running fine until Sunday when it backfired and started running like crap. This is a 3.2 with motronic. The fuel and spark are controlled by the computer so timing is somewhat a non issue. The number 1 cylinder is apparently getting a backfire or detonation in the intake manifold for some reason. The plug is wet with fuel whenever I pull it out and check. If I pull the plug wire or pull the injector connector then the detonation goes away so I know it's in number 1 cyclinder. I checked for a broken rocker arm, spring etc and there seems to be some play in the valve at TDC. I haven't measured the gap yet. I pulled a quick compression test and am getting compression although it appears low at first pass. I have fuel, probably too much, spark and air. The real issue seems to be in the cause of the intake detonation. Is it an intake valve that isn't closing, is it a faulty fuel injector that's just running or dripping excess gas, is there a faulty speed or reference sensor? I'm not sure on these and that's where I am now. Any suggestions are welcome or ideas.

You could have low compression because you didn't pull all the plugs and the engine isn't turning over fast enough.. When I rebuilt my engine I managed to damage one of the injectors putting the intake assembly on by myself. I knocked the tip off and the fuel just dripped out fouling out that plug. I think it's spark related, wires mixed up or some how sparking when the intake valve is open. I would check the distributer, cap and rotor.

Tim

Tim,

You are correct I did not pull all the plugs just the number 1 as I wanted a quick check to verify that I did or did not have compression. It's got new wires cap and rotor and I checked all those last night again. It's only happening on #1 and I swapped plugs and wires and those aren't it. I just keep comming back to the wet plug at number 1. I'll be checking the gap on the valve and rocker and re-doing the compression too. I'm stumped other than maybe pulling that injector out and swapping it if everything else looks good. Is yours a 3.2 and if so how hard to pull the injectors, it doesn't look too hard.

Dan O
3.2

if you can feel the valve clearance by rocking the rocker with your fingers, then that's sufficient evidence that the valve is not being held open. proper clearance is not an issue for this diagnosis, you just need to know that there is some. i would highly recommend a leakdown test on all the cylinders, just so you know the facts. a good valve grind should show about 4% leakage, hot, with the rings oiled. it would be interesting to see what #1 shows. an injector may well be stuck open, which could cause a backfire up the intake, but you would have to replace it to find out, because with the way they're clamped between the fuel rail and the intake, you can't really check the spray pattern. may be worth a shot.

My car is an 84 3.2. It's not that hard. Disconnect the fuel line, the injectors are held in by the fuel rail. just pull the clips at the top of the injectors, loosen the rail then the injectors just pull out of the intake. I can't see how flame is getting into the intake unless there is spark when the intake valve is open??

Tim

John,

How hard is it to pull the whole bank off and swap an injector? It looks fairly straight forward to me but I can't see the back of the fuel rail but presume there is a fuel line connected there. I'm still planning on re-doing the compression test tonight and double checking that valve for clearance just to be sure. No thoughts on a bad or misaligned sensors? The leakdown will be done to when it goes back to the shop just for comfort even if I find the injector to be the problem.

Dan O

My car is an 84 3.2. It's not that hard. Disconnect the fuel line, the injectors are held in by the fuel rail. just pull the clips at the top of the injectors, loosen the rail then the injectors just pull out of the intake. I can't see how flame is getting into the intake unless there is spark when the intake valve is open??

Tim

as far as backfiring up thru the intake goes, have you ever seen a car with carbs that were way out of adjustment, or leaking internally, spit fire out the carbs when it's revved up? the valves can be fine, and it can still do it. 'nuff said?