No spark on #3 and #4 Cylinders?

[subaruVWnut]

I recently purchased a 98 Outback w/ an engine problem. It has the DOHC 2.5L .Trying to diagnose the problem.

 

Rented and OBD-II code reader which shows "misfire on #3 and #4 cylinders". So far I've swapped the ignitor and the coil.....with no success.....still no spark on 3 and 4.

 

Plan to check continuity on wiring between ignitor and the coil.

 

I'd appreciate any other diagnostic tips.

 

Warren C.

[Legacy777]

Does the engine run, or is it just that you're getting CEL's for misfires.

[subaruVWnut]

The engine starts and runs.....anemically..of course on two cylinders.

 

Initially I got CELs for misfire on 3 and 4 cyls....then after clearing the codes and running it for awhile....the CEL didn't come back on.

 

Checking for spark in the number 4 plug spark by pulling a plug and holding next to the engine....no getting any spark arcing to the block.

 

Running the engine dumps raw fuel into the exhaust/cat...causing the CAT to glow red hot after running awhile.

 

Warren C.

[Adam N.D.J.]

I would also check the wireing from the computer to the ignitor. Usually if there is a problem with something that the computer uses, it will throw a code. Also if you are checking the spark on the #4 plug, the spark will acually come from the block and go to the wire. Waste spark systems are funny like that.

 

I'll dig around tomarrow and see if there is anything I can come up with when I'm acually looking at a schematic of the system that could cause this.

[subaruVWnut]

I would also check the wireing from the computer to the ignitor. Usually if there is a problem with something that the computer uses, it will throw a code. Also if you are checking the spark on the #4 plug, the spark will acually come from the block and go to the wire. Waste spark systems are funny like that.

 

I'll dig around tomarrow and see if there is anything I can come up with when I'm acually looking at a schematic of the system that could cause this.

 

Adam,

 

Appreciate your help.

 

Warren C.

[lmdew]

If you need the coil pack I have one $25+shipping.

[Gnuman]

If you need the coil pack I have one $25+shipping.

lmdew, thanks but the car has a brand new coil on it (someone else tried that already). I'm also working on this, and plan on checking not only continuity but signal from ECU to igintor, and from ignitor to coil. As you may have guessed, I'm working on this too. In case the coil was bad despite being new, we swapped one from annother engine that was running perfectly with no results. Those two components are ruled out.

[Adam N.D.J.]

Looked into it, and I have to say, this is a pretty simple system, mostly. The computer, with the help of it's input sensors commands the ignitor to fire the coils. This control is done over two wires, (yellow with a red stripe, and yellow with a violet stripe if I remember correctly, left my schematics at the shop unfortunatly). Given that the 1-2 coil isn't haveing any problems I would rule out the input sensors. This leaves the ignitor, coil pack, computer and the wireing connecting them all. I would check at the coil, see if it is being command on/off or not. If there is nothing there, then I would go down to the ignitor, if still no signal, check the continuity of the wires from the computer to the ignitor, if the wires check out to be ok, then it is probally safe to say that the quad-driver in the computer is prolly burnt out, and thus, it would need a new computer. Lemme know what you find. Lotsa luck. . .

[alia176]

How about the input sensors like crank shaft and possibly the cam shaft sensors? Also, there's a relay under the dash, on the driver side somewhere that contributes to this type of error, particularly #3 misfire. This relay needs to be replaced as the contacts wear out. Do a search on #3 Cyl misfire or P0303 and eventually you'll come up with this thread.

 

Ah, found the thread

http://www.ultimatesubaru.org/forum/showthread.php?t=20291&highlight=sea%233

 

but it talks about stalling due to this error. May help you out!

 

Good luck.

 

Ali

[B99Brighton]

I had a similar problem when i swapped an engine in a 90 legacy. every test i performed turned out ok sensors, coil, wiring, etc. I really was frustated at this point. When I unpluged the main harness from the engine to the harness that leads to the computer, near the fuse box, it had a bent tab in the harness plug. it had been bent over when we plugged it in causing the same two cyilnders to be inactive. of course we bent the small male spade straight again and connected the harness and it was all cured. I don't know but it's possible that this same thing has happeded. or the wiring could have been pulled on and created a bad connection at the connectors. check that first before going through all the sensors and diagnostic procedures. It is the main engine wiring harness plug, there are three total plugs in that area.

good luck!

 

 

 

I recently purchased a 98 Outback w/ an engine problem. It has the DOHC 2.5L .Trying to diagnose the problem.

 

Rented and OBD-II code reader which shows "misfire on #3 and #4 cylinders". So far I've swapped the ignitor and the coil.....with no success.....still no spark on 3 and 4.

 

Plan to check continuity on wiring between ignitor and the coil.

 

I'd appreciate any other diagnostic tips.

 

Warren C.

[Gnuman]

We found the problem. The ECU was faulty. we checked continuity between ignitor and coil, then between ECU and ignitor, and all that was good, so we swapped out the ECU from annother 98 Outback and #3 and #4 started firing like champs. Hey Jamie, how much do you charge for an ECU for a 98 Outback (manual tranny), or do you need a part number for that? I can pull the model code from the old one, or send you a VIN. PM me please.

[subaruVWnut]

Looked into it, and I have to say, this is a pretty simple system, mostly. The computer, with the help of it's input sensors commands the ignitor to fire the coils. This control is done over two wires, (yellow with a red stripe, and yellow with a violet stripe if I remember correctly, left my schematics at the shop unfortunatly). Given that the 1-2 coil isn't haveing any problems I would rule out the input sensors. This leaves the ignitor, coil pack, computer and the wireing connecting them all. I would check at the coil, see if it is being command on/off or not. If there is nothing there, then I would go down to the ignitor, if still no signal, check the continuity of the wires from the computer to the ignitor, if the wires check out to be ok, then it is probally safe to say that the quad-driver in the computer is prolly burnt out, and thus, it would need a new computer. Lemme know what you find. Lotsa luck. . .

 

Adam,

 

Your suggestion is pretty much the proceedure we followed:

1. Swapped Ignitor with known good one......no luck.

2. Swapped coil with known good one........no luck.

3. Checked continuity of wiring between ignitor and coil .....good.

4. Checked the chassis ground to the ignitor.....good.

5. Checked continuity between computer and ignitor.......good...so it looks like it has to be a problem in the computer.

6. The problem car is a standard shift and I don't have a spare 96-98 computer...much less one for a 5 spd. The other car available that we grabbed the coil and ignitor from is an automatic. I decided to risk swapping the computers ....didn't expect everything to run properly....but thought I might at least... find out if a different computer would get all the cylinders to fire..??? I was worried I might damage the good computer in the automtic car.......but I'm the impatient type....so went ahead and swapped the auto ECU into the 4spd problem car.......

 

Sure enough....still didn't run well...idled terribly and starting throwing off a bunch of troube codes......but with the throttle open...all cylinders are firing...

 

So it looks like a bad ECU......and I'm in the market for a working ECU for a standard shift 98 Outback.

 

The computer seems to have survived the test when put back into the automatic Outback...although the check engine light is on...hopefully a residual from the other car......and will go away when I dump the codes.

 

Anyone know where to get a reasonably priced ECU.

 

Also damaged one spark plug wire.....man are those things hard to get out on a DOHC 2.5L ...are there some secret tips

 

Warren C.

[Lawsonmh15]

Adam,

 

Your suggestion is pretty much the proceedure we followed:

1. Swapped Ignitor with known good one......no luck.

2. Swapped coil with known good one........no luck.

3. Checked continuity of wiring between ignitor and coil .....good.

4. Checked the chassis ground to the ignitor.....good.

5. Checked continuity between computer and ignitor.......good...so it looks like it has to be a problem in the computer.

6. The problem car is a standard shift and I don't have a spare 96-98 computer...much less one for a 5 spd. The other car available that we grabbed the coil and ignitor from is an automatic. I decided to risk swapping the computers ....didn't expect everything to run properly....but thought I might at least... find out if a different computer would get all the cylinders to fire..??? I was worried I might damage the good computer in the automtic car.......but I'm the impatient type....so went ahead and swapped the auto ECU into the 4spd problem car.......

 

Sure enough....still didn't run well...idled terribly and starting throwing off a bunch of troube codes......but with the throttle open...all cylinders are firing...

 

So it looks like a bad ECU......and I'm in the market for a working ECU for a standard shift 98 Outback.

 

The computer seems to have survived the test when put back into the automatic Outback...although the check engine light is on...hopefully a residual from the other car......and will go away when I dump the codes.

 

Anyone know where to get a reasonably priced ECU.

 

Also damaged one spark plug wire.....man are those things hard to get out on a DOHC 2.5L ...are there some secret tips

 

Warren C.

 

Have you switched plugs within the last 3,000-10,000 miles? I put in some bosch plat. + 4 plugs in and after about 7,000 miles started getting the PO303,304 codes. Swapped with NGK V-Power. No more CEL.

 

The other thing I noticed, was that the metal lug inside the plug wire boot was extending further down the boot than the others. Good Luck.

[Cougar]

If you haven't looked inside the ECU to see if you can fix the problem I would check it out. Sometimes the problem can be due to a simple bad connection and just repairing the connection will fix it up.

[Adam N.D.J.]

More than likely opening up a computer will do nothing more than give you a headache. I've been inside a good number of computers, built a couple, and half the time, even though I know what I'm looking at, it still gives me a headache.

 

The Auto computer isn't going to run right in a manual shift car for sure. For instance one of the sensors that the computer looks at is the Park/Neutral sensor, which the manual car won't have (just a neutral safety switch, completely different).

 

Computers can vary greatly between models and years, even with the same engine and everythings else. Most of the time when you get a new computer, it either has to have the PROM changed/flashed/or programmed. As far as the CEL coming on in the donor car, it won't be from the car that you used it in, as when you took it out of the car, and removed power from it, it lost all the code info for that car, so you should look up what that code it has is, may be important.

 

Computers can be kind of spendy, but from past experience, I've found that getting a new one is 9 times out of 10 a better choice (unless it's a GM with (e)PROMS in it). Had way too many problems with used ones not running right, in one way or another.

[Cougar]

I have repaired several ECU's in the past though they had transistor and IC problems and not just a bad connection problem. One member here just repaired his ECU that had a bad internal connection for the injector circuit. Repairing a ECU can be done fairly simple sometimes, depending on the situation.

[subaruVWnut]

I have repaired several ECU's in the past. Though they had transistor and IC problems and not just a bad connection problem. One member here just repaired his ECU that had a bad internal connection for the injector circuit. Repairing a ECU can be done sometimes, depending on the situation.

 

I'm electronics "challenged" but would be glad to send my ECU to someone qualified to check it out.

 

Any volunteers?

[subaruVWnut]

I'm shopping for an ECU on www.car-part.com and can't figure which part of the part numbers indicate which ECU is for a 5spd tranny version vs an automatic.

 

My ECU part number is:

 

22611 AD60A

JA18000DK9 7902

 

Can someone tell me how to tell the difference.

 

Warren C.

[Cougar]

I'm shopping for an ECU on www.car-part.com and can't figure which part of the part numbers indicate which ECU is for a 5spd tranny version vs an automatic.

 

My ECU part number is:

 

22611 AD60A

JA18000DK9 7902

 

Can someone tell me how to tell the difference.

 

Warren C.

 

I looked at the web site and it looks like your car is a manual with a 2.5L engine, correct? Since you appear to live in California does the car have the California emissions system? It looks like there are at least a couple ECU's that would work and be under $100 dollars.

 

I would be glad to look at your ECU if you would like. I can't promise I can fix for you though, but will try. The site you gave for parts has some real good prices for a replacement so it may be better to get one from them and see about getting yours fixed as a spare to have on hand, if that is really the problem. See if the replacement works first before sending it. If you want me to look at it let me know and I will send you my address.

[DAlgie]

Pretty sure that a misfire code isn't just that there is no spark. Also, you need to ground the spark plug to the block, not hold it away, otherwise you are forcing the ignition to jump TWO gaps, which is hard to do normally. The misfire code is telling you that those two cylinders didn't fire, but that might not be ignition. Possibly that bank has bad leakage, blown head gasket even. An engine needs compression, reasonable quantity of fuel, and spark at the right time to run.

[subaruVWnut]

I looked at the web site and it looks like your car is a manual with a 2.5L engine, correct? Since you appear to live in California does the car have the California emissions system? It looks like there are at least a couple ECU's that would work and be under $100 dollars.

 

I would be glad to look at your ECU if you would like. I can't promise I can fix for you though, but will try. The site you gave for parts has some real good prices for a replacement so it may be better to get one from them and see about getting yours fixed as a spare to have on hand, if that is really the problem. See if the replacement works first before sending it. If you want me to look at it let me know and I will send you my address.

 

The car was originally from Texas. It's a 5 spd with a 2.5L DOHC.

 

I plan on buying one of the used computers with some kind of guarantee that it will work ....or money back...But what I need to know right now is how to tell which of the computers available is for a 5 spd...vs. automatic.

 

Some of the listings show part numbers the same as mine except for the last four digits.

 

Which part of the part number determines 5 spd or automatic version.

Warren C.

[subaruVWnut]

Pretty sure that a misfire code isn't just that there is no spark. Also, you need to ground the spark plug to the block, not hold it away, otherwise you are forcing the ignition to jump TWO gaps, which is hard to do normally. The misfire code is telling you that those two cylinders didn't fire, but that might not be ignition. Possibly that bank has bad leakage, blown head gasket even. An engine needs compression, reasonable quantity of fuel, and spark at the right time to run.

 

You could be right that the problem may be more than the ECU...since this car is new to me and "not running" when purchased. But we definitely had no spark on cylinders 3 and 4 and with all systems (ignitor, coil, wiring) checking out OK from the ECU through the coil...plus..when the computer from other car was substituted ...we still had lots of other issues with poor running..mostly at idle....but all cylinders were firing on full throttle....which didn't happen with the original ECU.

 

Just trying to follow a logical process of diagnosis...and this is where we are so far.

 

I haven't done a compression or leakdown check yet..figured I needed all cylinders firing as the first order of business......man are the plugs hard to get to with these DOHC engines. Already ruined one plug wire, just trying to get it off the plug.

 

Also need to buy one good plug wire for #4 cyl.

 

Warren C.

[Lawsonmh15]

You could be right that the problem may be more than the ECU...since this car is new to me and "not running" when purchased. But we definitely had no spark on cylinders 3 and 4 and with all systems (ignitor, coil, wiring) checking out OK from the ECU through the coil...plus..when the computer from other car was substituted ...we still had lots of other issues with poor running..mostly at idle....but all cylinders were firing on full throttle....which didn't happen with the original ECU.

 

Just trying to follow a logical process of diagnosis...and this is where we are so far.

 

I haven't done a compression or leakdown check yet..figured I needed all cylinders firing as the first order of business......man are the plugs hard to get to with these DOHC engines. Already ruined one plug wire, just trying to get it off the plug.

 

Also need to buy one good plug wire for #4 cyl.

 

Warren C.

 

LOL. I reiterate my first response. Plugs?!!! It boggles my mind that people will skip over the cheapest and look at the expensive option first. Plugs = $12. Pulling them = Free. Like I said. Had the EXACT same codes, wound up being plugs or wire. NO CEL's since.

[Cougar]

You could be right that the problem may be more than the ECU...since this car is new to me and "not running" when purchased. But we definitely had no spark on cylinders 3 and 4 and with all systems (ignitor, coil, wiring) checking out OK from the ECU through the coil...plus..when the computer from other car was substituted ...we still had lots of other issues with poor running..mostly at idle....but all cylinders were firing on full throttle....which didn't happen with the original ECU.

 

Just trying to follow a logical process of diagnosis...and this is where we are so far.

 

I haven't done a compression or leakdown check yet..figured I needed all cylinders firing as the first order of business......man are the plugs hard to get to with these DOHC engines. Already ruined one plug wire, just trying to get it off the plug.

 

Also need to buy one good plug wire for #4 cyl.

 

Warren C.

 

Since the other ECU made a change for the good then it appears you do need to change the ECU. I don't think the last four digits makes any difference (it may be a date code) but I would contact the seller and ask them to see if they can say for sure.

 

Don't be afraid to open up your ECU and just see if you can find a problem with the unit, starting at the pin that ties to the coil unit that is having trouble.

 

I would use NGK platinum of iridium plugs if you don't have them installed already and assume you have already checked the plugs and wires for a problem. I think by twisting the boot side to side and pulling on the plug wire it will help remove it. Using a very thin coat of silicone grease on the plug insulator will help get the boot off in the future.

 

I would hold off on the compression tests until you get fire to the plugs but if you have the plugs out it wouldn't hurt to know how much the pressures are in each cylinder.

[DAlgie]

I guess realising how the ECU determines that there is a misfire is in order. It looks at a notched wheel on the crank through a hall effect (or similar) sensor and measures the time between each notch, comparing this to a formula with rpm. It knows how much less time there is between all of these notches after a cylinder fires. In other words, the crank is accelerating and deaccelerating with each firing impulse and cycle in between, if the time between notches drops out of the table it's comparing to, this is seen as a misfire on that cylinder. No thought is given to what caused that misfire, just that it didn't fire. Older systems (OBD1?) didn't have this ability, therefore if you had a problem and no check engine light then first order was to look at the ignition, there was no system to check this normally.