Just installed a used low mileage 2.5L with tip into a '98. Fired up okay with a little backfiring into the intake, I think. Engine hunted a bit while the DME learned. No leaks or obvious problems. Let it run to heat up and noted that it was running rougher than expected and exhaust didn't sound smooth - more like an ignition type of problem.

After 10 minutes, I saw red in the driver rear wheel opening and found the cat was cherry red. Passenger side was fine. Immediately shut it down to cool. Durametric showed a P0157 20 code which is bank 2 O2 sensor 2. I checked wiring and condition of sensor and all looked well. There were no other fault codes at all. Erased code and restarted. Still running too rough and got a minor initial backfire sound. Checked all injectors to make sure they were connected, and they were okay. Durametric showed no codes.

I'm guessing next step is to remove plugs and inspect, do leakdown. But what should cause this condition? Wrong cam timing would throw a code. Almost all faults I can think of would throw a code. I'm wondering if a bad injector could cause this? False air (checked and didn't find anything suspicious, but it's still possible).

Ideas?

 

which points to at least a leaking injector.

Since engine controller can't know which injector at fault it will restrict fuel injection over all cylinders of that bank. Thus if one injector leaking and causing excessive rich condition (at O2 sensor) one cylinder running 'rich' and 2running lean. Hence the backfire which is usually a sign of lean running.

I'd not suspect cam timing unless you tell me that's been messed with recently. If engine apart and cam chains/tensioners/etc. disassembled and then put right again... well, last thing touched is always suspect #1 when symptoms appear.

Even cam timing unlikely to cause the type of hot running you are seeing. Engine may run rough, spit back, or even try to run backwards or not run at all if valves open and pistons contact open valves, but overheating not a symptom of cam timing I'm familiar with.

Might pull injectors on the affected bank and see if you can spot an injectory with obvious signs of distress. Some shops have ability to hook up injectors to electronics and injector cleaner supply and in clear housing observe spray patterns and flow volume. Very quickly then the underperforming injector or injectors make themselves known.

If you spot a bad injector or injectors replacing them outright might be a good stab at a solution. Unless cost prohibitive replacing all 3, using a shotgun approach and replacing all possible offenders on that bank, might be a solution.

One possible way to ID bad cylinder is to start engine dead cold let idle a moment then shut off engine. Very carefully check and compare exhaust runner temperatures. The coldest one (or hottest one) likely the bad cylinder.

Actually cylinder may not be hot because it is not running very well. But the unburned fuel is being burned in converter and that's why the converter glowing red hot.

After you get fueling sorted out though converter and O2 sensors on that bank may be shot.

Sincerely,

Macster.

 

Thanks, Macster - just the kind of feedback I'm looking for. After sleeping on it, I pretty much decided it had to be excess fuel either due to injector(s) or missed ignition.....or possibley false air associated only with that bank. Missed ignition would show up on the Durametric. The engine mechanicals have not been touched, so it's highly unlikely a timing issue as you point out.

I do have an infrared temp sensor, so your idea about checking exhaust runners is a good one and quite easy.

Since this is a used engine, I still have the original standing by - which means a spare batch of injectors and pretty much everything else. Will definitely take a look at that.

Thanks again.

 

This engine may have the old-style oil seperator. Replace that and check again. Backfire through the intake is associated with lean running.

 

I doubt it's that. I've seen a 996 with an oil seperator that completely failed. Only cause massive white smoke clouds from exhaust(to where I couldn't see the car),the cats never turned red. Also if it was the oil seperator wouldn't it be affecting both sides of the exhaust?

 

Okay, just got back from the maiden drive with the new drivetrain. Good news is nothing major to worry about (I hope) and the tranny seems to work as advertised. And yeah baby, these things handle like go-carts.

I installed new spark plugs and it naturally seemed to run better - but still can tell it isn't idling as it should. Temp gun showed about 250 degrees on both cats, so that's why I decided to take it for a drive. At a stop, RPMs dropped lower than they should and it hunted a bit. After getting back into the garage (total drive was down the street and back), it died. Restarts okay but doesn't want to idle. Cats seemed okay and not overly hot. Duramtric shows no codes.

Still haven't done anything to the injectors. When first started cold, wants to backfire a bit into the intake with a little throttle applied, then after getting hot, doesn't want to idle. I'm now thinking air leak somewhere because this intake and fuel rails were okay before installing on this engine (transferred them from the original engine).

 

Just remembered......had a heck of a time figuring out which fuel line was supply and which was return at the connections on the floor. Could it be possible I've got them backward? Never mind.....lines are okay.

 

Looks like false air. At idle, covering the throttle body opening causes a slight dip in idle speed, but doesn't kill the engine. Playing around with it a bit, restricting the opening causes the idle to smooth out very nice and flat. When I installed the intake, the bolts were very, very hard to install. One of them broke off and I was able to get it out of the head with vice grips. I think there is some loctite left in there from the factory, and maybe I'm not getting proper torque on the intake. Next step is to try to reseat the intake.

 

All is well.......new spark plugs helped, but removing and reinstalling the #2 intake solved the problem. Runs great, idles smoothly, no overheating. Hope this little message trail helps others.

 

into each threaded hole to ensure threads clean and free of thread sealer. Blow each hole out with clean dry air. Treating each hole to a dose of some cleaner and letting it soak a while doesn't hurt, as long as hole not through and the cleaner can't get where it doesn't belong.

Be sure to cover hole with rag so blast of air doesn't blast stuff all over engine, face, or in your eyes.

Tap will remove any stuff that cleaner and air blast doesn't. Of course you should follow up tap stage with cleaner and blast. Depending upon engine history, who's been at it before, several of these may be necessary.

No need to try to cut threads deeper in to hole. Use a plug or bottom tap and go only until resistence from tap encountering incomplete threads at bottom of hole met. Then stop.

After you're sure holes clean and dry then test thread each bolt into its respective hole. You've of course marked/labeled or somehow recorded which bolt goes where when you were unbolting the -- in this case intake manifold.

And because you may not have been the first, or worst to work on this engine, you may find the wrong length bolts used.

You want the bolts to be of course not only the right diameter and thread style (USA/SAE or metric) but the right pitch too and the right length. Thread a too long bolt in a too short hole and when you torque it down torque wrench clicks but bolt not really tight.

In a worse case, tightening bolt causes the bottom of the bolt hole to crack. Leak or worse is the result.

Ensure each bolt when hand threaded into its respective hole down far enough to securely clamp down on whatever it is supposed to and still not against bottom of hole. Check/measure distance between mating surface of say block where intake seals to head to be sure this distance less than the thickness of the manifold flange and its gasket.

You want to be sure when you tighten bolt it clamps part down tight and does not bottom in its hole. You want the torque you think you get to represent the clamping force exerted by the bolt and not by the resistence of the bolt as it seats against the bottom of its hole.

Also, go easy on thread lube. Fill a threaded hole with heavy oil or grease and tighten bolt and you may create enough hydraulic force to crack the material around hole.

Follow proper bolt tightening steps/sequences and torque settings. More is not always better.

Sincerely,

Macster.

 

Macster....just wanted to thank you for such a well written procedure.

I had already determined old loctite was the culprit, which was cleaned from the bolts. I did chase the holes I could get to on the heads, but it's very tight in there with the intake just moved to the side. Used a Q-tip with cleaner to wash them out, and all bolts went in without restriction. Starting to rack up some miles - engine/transmission performing great. No leaks, correct temps, smooth idle. So far so good.