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SVT with sudden rough idle, power loss

19K views 81 replies 18 participants last post by  qweesy 
#1 · (Edited)
My SVT very suddenly started to run like crap. Here's the situation. Filled up with gas today. Car has been running quite well, got 29 mpg on the tank on a 250 mile trip. On the way home, a few miles from the gas station the car starts to lose power and runs really rough in gear or neutral. Sounds like rocks rolling around when I apply throttle, gargley and deep sounding. I coast to a stop in neutral, with the car stumbling the whole time. Shut it off. Turn back on and it can barely idle, requires throttle to keep from stalling. Runs terrible, sounds dangerous even. Shut it off. Called AAA and had it towed to my local shop. It's sitting at the repair shop for them to diagnose tomorrow. No CEL through any of this.

Hopefully its something simple, I'm suspecting fuel filter or pump... Better not be timing related since that was done 55k miles ago.

More info:
Car has 135k miles.
Fuel filter mileage unknown, could be quite old as the filter, bracket, and nuts are very rusted. (Which is why I haven't gotten to it.) No mention of it being changed by PO, who kept decent notes and was a Ford mechanic.
For past few months car has had a slight stumble at cruising speeds and occasionally threw P0133 and P0172. Changed O2 sensor, reset ECU, car has run much better since with no codes, but still not 100.0%.
Has Toms Tune. No issues with the tune AFAIK.
New Motorcraft copper plugs and CFM wires.
New Alternator.

Basically, I'll see what the shop has to say tomorrow, but I'll back up their thoughts with what the FF community has to say. [ffrocks]


UPDATE WITH RESOLUTION:

It was bad gas. Really.

Shop replaced the fuel pump and filter. Still ran like garbage, very difficult to start it. Sat for a few weeks in the cold. Tom (1turbofocus) helped me get it started and debugged. I got the car running with the gas on intake trick. Once it was warm it ran ok, but felt down on power, like 50%. Figuring it might just be as simple as bad gas, I put some Heet and Seafoam in the tank and tried to drive it off. Put 100 miles on and it ran better as it went, almost completely back to normal. Still had a small hiccup between 1500 and 2500 rpms, usually in second gear. Filled it up with gas again and let it sit overnight in the cold. It fired right up the next morning. Ran better and better over the next few days, and no issues since. Boo Citgo!
 
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#39 ·
Gonna update my to-do list.

1. Compression check. Should be at least 100 psi. Move on if ok. Stop if any one cylinder significantly below that. Pull out hair.
2. Spark test. Check for spark at each plug. Move on if ok. If not, double check boot wiring/fit, and coil wiring/connection. Consider replacing coils.
3. Crankshaft position sensor. Can this be tested with voltmeter or datalogger?
 
#41 ·
I agree, it should. That's what's kind of frustrated me about this. No CELs. *In Kramer voice*: "Why don't you just tell what is wrong with you?"
 
#45 ·
If the Crank Position sensor was messing up you wouldn't get any spark. No crank sensor no spark. I would pull the valve cover off and see if the cams are still in line, if not then it's out of time. It's easy to do, also check the coil pack connector who knows, maybe the wires are getting pulled out of the plug?
 
#46 · (Edited)
...also check the coil pack connector who knows, maybe the wires are getting pulled out of the plug?
I can't stress how much it *might* be the coil. My ZX3 didn't run for shit when it went. Like I said, I'm pretty sure it's internally split in two, so you'd have good spark on two cylinders, and not on the others...certainly enough of a problem to keep it from running.

I hate to say it, but if it's not the coil, I'd start suspecting the timing is off...
 
#50 ·
I'm assuming the car has COP? Or if not it's a waste ignition system.

I've blown coils on waste ignition systems (on a 4 cyl) and on COP - they usually idle okay or rev okay, but any load at low RPM is hard.

Any time I have blown a coil (even one taking out half of the cylinders), the engine always runs.

There's a sensor not working somerwhere or the timing belt slipped or maybe t-belt tensioner failure?
 
#54 ·
^^ too funny...he believes in aliens and is excited for the end of the world....what a positive guy!

now back on track....def wanna know so I can check some stuff.
 
#55 ·
Buddy4679, I had a bad vacuum leak that caused the symptoms you described, it turns out a nipple on the back of intake manifold right after the TB had broken off, it's a port for the EVAP system and basically left a 1/4" hole in the intake manifold. I have no idea how or why mine broke but I'd be surprised if my car was the only one with this problem.

swansong, what did the shop tell you? They should have done a spark test, they're straight up incompotent if they didn't, it takes like 3 minutes. They should have also already done the compression testing to verify that timing was still right.

And BTW, if you do the compression tests, don't neccessarily condemn anything if you get compression but it's lower than 100 psi. My car does between 75-80, which concerned me, and then I did leakdown testing and those results were good, 5% loss on 3 cylinders and about 10% on one. Plus the engine runs fantastic, so I'm kind of not worried about it anymore. Also there's something weird with my starter and it kicks out after a few seconds of cranking and that makes compression testing kind of a pain and maybe inconclusive in my case. I've heard that VCT somehow causes misleading compression test #s but I'm not positive on that.
 
#56 ·
As far as I know the shop did not do a spark or compression test. They wanted an extra $80 to do a vacuum leak smoke test, AFTER they had replaced the fuel pump and filter and it still wouldn't stay running. At that point I gave up on them, so they towed it home for me for no charge.

Been reading into compression tests, and yeah its more important that all cylinders give similar numbers rather than reaching a specific number, especially with the SVT and its VCT silliness.
 
#57 ·
As far as I know the shop did not do a spark or compression test. They wanted an extra $80 to do a vacuum leak smoke test, AFTER they had replaced the fuel pump and filter and it still wouldn't stay running
I'd have b!tch slapped them six ways to Sunday. I can't believe how incompetent some shops are -- I mean, I'm no master mechanic, but seriously...

Anywho...let's hope it's something simple and easy, like the coil...

I guess a big ol' vacuum leak would do it too, so poke around for anything blatant.
 
#58 ·
Car still won't start. Here are some results though:

1. Timing belt looks great. I removed the screws holding the cam cover on and could bend the cover enough to peek at it. I checked the condition of the belt and teeth, marked the section with Sharpie, turned the engine over slightly, and repeated until I could see that the entire belt was in good shape. No teeth missing. Phew.

2. Compression is good. Cyl 1 = 125 PSI, Cyl 2 = 105 PSI, Cyl 3 = 105 PSI, Cyl 4 = 110 PSI. Phew #2.

3. Spark looks ok. That's according to my spark tester thing, which goes inline between the wire boot and the plug, flashes consistently on each cylinder when turning the engine over. I'm not sure exactly how bright this spark should be, but it's bright enough to see in the dark, but not crazy bright.

Observation: I think I need a new valve cover. Spark plugs 2-4 all had oil on the threads. The firing end looked normal, but there was some oil present, not sure if that is due to fouling or oil dripping on them when I removed them. I'm probably going to replace them, even though they have low miles, when I re-do the valve cover gasket. Is it possible that this is causing my no-start? Maybe, if all the plugs are fouled out... Of course no local parts stores have the plugs and gasket in stock, so I'll have to wait a day or two to get them.

So, it appears that I've got compression, spark, fuel, and the timing is ok. What's next? Still no CEL light.

Also, all this time I've been assuming I have fuel. The fuel pump turns on when key is turned to run, and my SCT log shows Fuel Pressure PSI is about 45-50. Does that mean that I've got fuel actually going into the cylinders? Could my injectors have issues..? Anything else I could log on the SCT?
 
#59 ·
So I bought some starting fluid (ether) and sprayed it into the intake box. The car started up, revved to 2k as usual, sputtered out and stalled. It wouldn't idle.

After a few more tries, I can get it to start up on most tries, after a few seconds of cranking and some throttle application. It will kind of idle for about 5 seconds, then stall. During this "idle" it sounds kind of like a Harley, lots of odd popping and snorting sounds at odd intervals. This is how it was running the very first time I tried to restart it on the side of the road when it first started running goofy. "Back to square one", in a way. Oh, and sometimes when I do start it up and it revs up to 2k or 3k, it sounds pretty normal and functional.

IAC?
CPS?
Timing issue..?

Ok, as I was typing this, I gave it a few more tries to start. Can't get it to start up now. It's like my ether ran out and it's not getting fuel again. Leaning towards fuel issue.
 
#60 ·
I've been pounding the hell out of the search feature (pro-tip to those using search, I actually have better success with Google: search site:focusfanatics.com *problem here*)

Sounds like it might just be the plugs crapping out from the valve cover gasket leaking. I've got the gasket and Motorcraft SP-463's on order at my FLAPS (of course, no one stocks SVT parts), but I might pick up a close-enough set of plugs tonight at Wally World just to see if that's what it is.

From reading threads, CPS should always throw a code when it goes out, so I'm ruling that out for now.

Still could be a fuel/injector issue, but plugs are much cheaper so I'll try those first.
 
#61 ·
Well you mostly got good news in that it's not a catastrophic timing failure. I think the fact that you have spark means the CPS is sending plausible info to the PCM and it's responding to that, as far as I know spark (and injector) timing depend primarily on the CPS. And like you said CPS failure should trigger a CEL and no engine starts of any kind. If it were an IAC problem, you should be able to start and keep it running with throttle. And I'm pretty sure the spark tester you bought means the plugs are sparking also, if you have spark at the tester it means that voltage also went through the plug and to ground since it's all inline.

I've had a periodic no start problem in past winters that's a bit like you have, long cranking time and very rough low idle. It's only happened a few times, but once at the suggestion of a friend I disconnected the MAF sensor and it started and ran normally. I looked at the MAF readings later on and it looked totally normally, and it hasn't happened this winter yet. Spark and fuel timing are dictated primarily by the CPS and then inlunced by the MAF sensor which is the primary measure of engine load. I think it's worth a shot given how easy it is. If you refilled the tank right before this happened, I'd also contact the gas station and ask if they've had any problems with gas quality in that time frame. Really unlikely but technically possible. It's worth changing the valve cover gasket but I don't think that's your problem, all 4 cylinders would need to have simultaneously flooded with oil and I don't see that happening.

I just noticed you've got Toms tune, have you sent him a datalog or contacted him yet? He's always telling people to send him datalogs, I have to assume the SCT has the capability of logging useful info. I realize the car isn't running and I'm not familiar with the SCT, but a key on engine off datalog might reveal a sensor spec that's wildly out of line. I kind of think that's what it is, all 4 of your fuel injectors can't have crapped out at once and they're individually controlled, you've got a new fuel pump and filter and good pressure, engine timing must be right based on the compression test. Spark is there and I don't think it would be without reliable CPS info. Or you somehow got fuel so shitty it won't burn.

Best of luck dude, you know you got good news when you did the compression testing.
 
#62 ·
Long post ha, so I'll summarize and say I agree with everything you said.

I just tried running it without the MAF connected. Same thing. Also had new plugs in, which didn't help sadly.

I did send Tom a datalog, and he told me to give him a call to go over some things, the first if which being a compression test. I'll call him again tomorrow. I know the SCT can dialog a lot of things, just not sure which PIDs correspond to the things I'd want to look at. Tom could certainly help there.
 
#63 ·
No work getting done today, too damn cold in the garage. Almost 10 below outside, and 20 mph winds.

Any other suggestions? I'll try anything at this point...
 
#64 ·
Finally got this one figured out. [grinking]

Turns out the problem was, really, no problem at all.

Tom (1turbofocus) and I had a trouble shooting session. Here's how it went down:
  • Checked intake boots, crank position sensor, and re-checked for spark. All came back good, but the spark seemed "weak".
  • We set up an SCT datalog and had the key in the ON position for the remainder of the troubleshoot. Tom wanted to first get the car running. We used a gas-soaked rag on the intake, before the MAF, and WOT to try to get it to run. It allllmost caught. A few more tries failed.
  • Here's the fun one. I removed the fuel pump fuse, and started it with WOT again. It was able to run, but still couldn't hold an idle.
  • With the throttle at WOT, replaced the fuel pump fuse. It started up again, same condition. How or why the car started without the fuse in I have no idea, and frankly I don't care anymore lol.
  • The car ran like absolute garbage at this point. Lots of backfires throught the intake, seemed to not be running on all cylinders, and tons of smoke from unburnt gas out the exhaust. I could kind of keep it running with the throttle, but it would barely respond to throttle input. WOT would barely raise the RPMs. At this point, I personally would have shut it down for fear of damaging the engine through timing issues or otherwise. Tom urged me to push on.
  • Eventually, the car started to get closer and closer to operating temp. As it got there the idle and running condition improved bit by bit. Things were looking ok...
  • By the time it got to 180 degrees, which took forever with the cold temps here, it was running as normal as it could be.
  • A short test drive confirmed that the car is back to normal.

Our theory was that the spark plugs were so fouled out by all the starting attempts that they just needed to get hot to un-foul themselves and allow the car to run. To get an idea of how much gas was sent through in the past week, I started this with a full tank, and put 2.2 miles on before the issue started. I'm now at 7/8ths of a tank lol. Those plugs didn't stand a chance. I'll be replacing the plugs.

TL;DR: It was the fuel filter and fuel pump. By trying to get the car to start again, the plugs fouled out. Once the car could be started and reached operating temp, the plugs were happier and the car ran great.
 
#65 ·
Glad you got it figured out. Mine did the exact same thing on a trip back through Texas. Fuel pump was the culprit.
 
#66 ·
Looks like I'm not out of the woods yet...

Tried to start it today, no go. Plugs are new now. Eventually I got it to start using the same method as yesterday, a gas soaked rag on the intake. It ran like crap until warm, when it ran somewhat normal. What is odd is that during the warm-up and even when it was warmed up, it was like the car switched modes from "normal" to "crap". During 'crap' mode, the car would have a rough, ugly idle at around 600 rpm. It would not respond to throttle input, even WOT. Eventually the car would switch to "normal" mode and would idle at 900, and responded to throttle. I took it for a drive at this time and it was mostly normal-going, until it started to crap out again halfway through. Back in the garage it continued to idle like crap and not respond to throttle. Code P0171 (lean condition) popped up during this time.

So the car runs well sometimes, and runs like crap most of the time. It is difficult to start when cold, seems like its getting flooded.

Could it be the fuel pressure sensor? Regulator?
IAC?
TPS looks like it still works just fine, I have a scan tool and it always reports correct percentages.
Faulty injector? Could one be leaking or plugged?
Bad ECU?
 
#67 ·
I'm thinking injector issue. This thread shows a similar issue where the solution was a fuel injector o-ring: http://www.focusfanatics.com/forum/showthread.php?t=283884

Any other suggestions? I'm getting to the point where I have to start throwing parts at it or take it to the stealership, neither of which I want to do yet...
 
#69 · (Edited)
Just read through this thread hoping it could help me with a slightly similar problem I am having with my stock 03 and stock tune.

My car does start, but hesitates a lot of the time. Then, once started, it is extremely lethargic until I'm up to operating temperature.
Really recently I lost my alternator, and had to have a new one put in (I was stuck in the middle of nowhere with no tools) and they decided to check out my CEL which had been on.
After four hours on the phone with Ford, the mechanic came back saying it was a very strange code and my PCM was bad. But then also admitted the car ran and drove.
Drove home from Florida to South Carolina, light still on, and at highway speeds it runs fine, but then will try and stall out at lights and so on.

Not sure if it is the same problem you are having, but I'd be looking to the PCM which as I'm just now learning is the same as the ECU?
I understand you have a tune on it, and you've reverted to stock, but I might think, given the amount you've already checked, that the issue might stem from the computer itself being faulty.

Anyway, I will keep reading and hopefully you'll have better luck than I have.
 
#70 ·
It is possible the ECU is bad, and I've had it suggested before. However, being an electrical engineer, I find it very unlikely that an ECU would just "go bad". They should be one of if not the most dependable electronic component on the car. I would be inclined to suspect many other parts before giving in and replacing the ECU as a last resort. In my case, I don't have any strange codes to suggest it, just strange operating characteristics.

All that said, strange things happen and it very well could be the ECU.
 
#71 ·
Fair enough. I find it especially odd that it would go bad with no warning. And in my case, go bad and still run fine for 400 miles.
This is going to sound oddball, but could there be a massive exhaust restriction on a few cylinders so the backpressure is backfeeding into the combustion chamber? Or a seized valve? (I seriously hope not for your sake) Beyond that I'd think you'd need to look for a random electrical issue that is grounding somewhere unseen.
 
#72 ·
Yeah I really think its a silly electrical issue somewhere. I can't get it to start on its own, but if I do get it going with creative methods it runs like crap until it gets warm. When its warm it randomly switches from running 100% OK to total garbage. Given that it can run well when it wants to, I think its something simple and electrical.
 
#75 ·
Yeah I really think its a silly electrical issue somewhere.
x2. I would suggest after reading your tthread and all your symptoms, you check the coil and coil connector thoroughly.

I had intermittent good/crappy running conditions such as yours and it turned out to be the coil connector. What I believe was happening was that, once warm, condensation or moisture evaporated or simple minor expansion of wires under heat restored the continuity of the wires enough to make the car run normally (still somewhat intermittent under load); during cool off, it was back to hard starting and poor runninng and the cycle would repeat.

Can you beg or borrow a substitute coil to try also? The intermittent may be inside the coil as well as being related to the connector. I'd aslo unwrap the black plastic coil connector harness sheathing back a good six or eight inches to trace the wiring and make sure all is well.
 
#73 ·
Have you replaced the coolant temp sensor? Not sure on exact name but its the sensor on the thermostat housing. The SPI is a different animal but had a odd problem with it. At cold it wouldn't start tried everything. Eventually it would but wasnt happy till warmed up. Finally one day the gauge literally went from one side to the other a few times or never would of found it. Good luck..
 
#76 ·
Have you replaced the coolant temp sensor?
I thought about that, but temp sensor reports good readings, both on the dash gauge and in my SCT logs.

Is the VCT working properly?
Ought to be. No codes about it being wrong, and it acted normal up to 6k rpm on one of the test drives where it was running ok.

x2. I would suggest after reading your tthread and all your symptoms, you check the coil and coil connector thoroughly.

Can you beg or borrow a substitute coil to try also?
The wiring and coil look ok, but looks can be deceiving. I can borrow a coil, and had in fact arranged to do so before I got it running again and thought I fixed the problem. I think the coil being bad is a more likely scenario than VCT or ECU, but I didn't really realize it could allow my car to be semi-functional like it is. I'll check it out more thoroughly.
 
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