98 v70 intermittent big misfire

kmashlan · Post by **kmashlan** » 26 Aug 2017, 23:05

Hi all.

Have been reading the threads, but so far a case of not finding anything that matches exactly so want to run some thoughts past you all to see if I am on the right track.

Symptoms:
Car runs extremely rough sometimes. It really only started a few days ago. I mean not a little misfire, but real shudder - enough to stall the engine. No power, incredibly rough running and a large fuel smell particularly from the exhaust. Other times, perfect. There is no code from the DTC - no faults found according to the computer.

Things I have done:

Scanned the codes - none found. Changed most of the ignition system - Cam position sensor, Leads, Coil (with ballast), distributor cap, rotor. Checked the plugs although have not changed them.

Observations:

I tried un-plugging one spark lead at a time and found cylinders 2 and 4 made no difference to rough idle, although later seemed to change. I did run the engine with the turbo intake off and managed a fairly large explosion while testing the leads - obviously a lot of fuel/air which I can only assume came from the turbo inlet, or blew up in the exhaust. However, after changing my pants (and putting it back together) the car ran perfectly. For 5 miles anyway.

I noticed after limping the car home the cat was ticking really loud - it was glowing. Never looked at it at night before, so that may be normal (the glowing), but it was "ticking" a lot louder than it normally does.

Also once or twice, it is has been hard to start. It starts normally and "fires" but stalls straight away. Then it seems like the starter motor is running slowly, but if I keep it turning after 15 seconds or so it will "catch up" - sounds like the little engine that could - I think I can, I think I can and starts to turn faster and faster until it starts, and then runs rough for 5 seconds, then settles and runs normally. I don't know if it is related, but has done that maybe three times over the last three years (replaced battery the first time) and only does it maybe once a year.

Questions I have:

1) I assume if I had poor compression, burnt valves or other serious engine issues it would not be intermittent?
2) A lot of issues mention MAF - could this cause this behaviour?
3) A blocked cat would again not be intermittent?
4) Could this be some sort of earth issue, which would maybe explain the slow starter motor symptom?
5) With the rich smell, I as thinking it is unlikely to be injectors/fuel pressure as when it is rough, it is also rich. Does that make sense?
6) I haven't changed the crank sensor. Would this trigger a code though?

Sorry for all the questions, but the random nature of this makes it seem more electrical than mechanical.

Cheers

Ken.

Post by **E Showell** » 28 Aug 2017, 05:34

Sounds like possible burned exhaust valve or two, but I hesitate to suggest that since no codes and burned valve will normally set a cylinder specific P0301, 302, 303, etc.

Glowing CAT wouldn't't necessarily be a burned valve symptom either.

Is the CAToriginal to the car? How many total miles?

Collapsed CAT internals can block exhaust gas flow. If the "ticking from the CAT" might be described as a "rattle"you may have found your problem.

If you end up replacing your CAT, take the old one to a metals recycler. They contain precious metals. I got $70 bucks for mine a while back.

Post by **kahl** » 28 Aug 2017, 06:24

I would disconnect the MAF and see what impact this has on how well the engine operates. I would also check the air intake from the air cleaner box to the throttle body for leaks.

Post by **E Showell** » 28 Aug 2017, 06:48

A simple compression test could rule out burned valves. For some reason, it seems like the '98s are more susceptible to valve issues.

Post by **erikv11** » 28 Aug 2017, 07:38

Starting with the MAF is a very god idea. Like kahl says - unplug it and drive around for a day. Does this change things? Look for air leaks. especially in the induction path.

While a simple compression test will definitely rule out burnt valves so it's not worth a ton of speculation either way, this does not sound at all like a valve issue. When there is a hole in a valve, that cylinder behaves the same (poorly) all the time. The car would never run "perfect" as described. And these cars run pretty darn well on 4 cylinders, nor do you expect to see "incredibly rough running" as described.

kmashlan · Post by **kmashlan** » 28 Aug 2017, 18:26

OK - Yes, I have since swapped a MAF in and no difference - although it did trigger a code with no maf connected. (Good...)

I will do a compression test as it seems a common thread.

kmashlan · Post by **kmashlan** » 31 Aug 2017, 04:50

OK - did a compression test - all 5 have 115 cold and dry. Not the best maybe, but it is a weird 2.0 motor which puts out 226hp so maybe compression is not that high normally.

Anyway, have replaced the MAF (and run the car without it) and no luck. It will literally run for 10 seconds perfect, then 10 seconds rough, then maybe 5 minutes perfect, before rough again. It it like someone is flicking a switch.

Possibly fuel pump? Although when running rough, there is a strong smell of gas, so more like the fuel is there, but not being burnt. Also, listening to the pump whirring while it is alternating between missing and smooth, there seems to be no change in it, not cutting out or stuttering.

Maybe of note, I did a test of the PCV and it looks like it is blocked up - smoke from the dipstick, or with the oil cap removed. Could this be the issue? I assume if enough "fumes" get into the inlet, it would stuff up the oxygen/fuel ratio pretty badly, but would this be on/off so much like I have described?

Cheers everyone for the suggestions.

Ken

kmashlan · Post by **kmashlan** » 31 Aug 2017, 04:56

E Showell wrote: ↑28 Aug 2017, 05:34 Sounds like possible burned exhaust valve or two, but I hesitate to suggest that since no codes and burned valve will normally set a cylinder specific P0301, 302, 303, etc.

Glowing CAT wouldn't't necessarily be a burned valve symptom either.

Is the CAToriginal to the car? How many total miles?

Collapsed CAT internals can block exhaust gas flow. If the "ticking from the CAT" might be described as a "rattle"you may have found your problem.

If you end up replacing your CAT, take the old one to a metals recycler. They contain precious metals. I got $70 bucks for mine a while back.

Hi.

The cat would be original (at least I haven't changed it in 10 years). Car had done 100K when I bought it and have added another 60K over the last 10 years. Not a rattle just an unusually loud cooling tick when the car is switched off. This seems to have settled down a bit though. Also, I assume a blocked cat would not be random on/off like it is behaving.

Ken

Post by **wizechatmgr** » 31 Aug 2017, 10:45

Good part to this is fuel pressure is easy to test. Could also be a fuel pump relay that is getting ready to go, with the contacts arcing. You should be able to jumper the relay to eliminate the relay as a potential cause of the issue.

What is the voltage at the battery with the car having NOT run for a full day? A low battery does all kinds of crazy stuff... My 99 literally wouldn't move when the battery went really low. Before that it acted just like you described fine for a second, then lunging and lurching, then worse... I believe I was down to around ~11.5V resting voltage after this started. My alternator went and I didn't realize it for about an hour an a half of driving. I can tell you this - our cars take more than 8A to run - even with headlights, etc all turned off.

I'd also suggest unplugging 1 injector at a time and see if you get a cylinder with no change in idle - it could be stuck open or closed. I know this will be difficult with the car running as it currently is.

kmashlan · Post by **kmashlan** » 11 Sep 2017, 01:48

Hi all... Just an update in case it helps.

I still have the issue. Have replaced the plugs, rotor, distributor, leads, coil, MAF, Cam position sensor and fuel pump relay. Voltage is 12.5v resting 13.5 running - the battery is pretty new. I thought I had it fixed, but then it came back. Still no error on the computer.

I notice that I have a strong fuel smell when it misbehaves. Maybe an injector is sticking open and flooding it? I tried disconnecting the injectors one by one, and they all seem responsive, but maybe if one is stuck open (or randomly sticks opens) that might account for why it doesn't create a code. When I did unplug them, the computer logged a code, but after clearing it, the rough running doesn't trigger anything. I have ordered some injectors to try swapping them out as well. Will see if that helps. Will try and find a fuel pressure gauge.

I have got a new PCV kit from FCP and will swap that out over the next few days. I must have put about twice the value of the car into it by now, but hopefully it won't beat me!

Ken