Lately I've been having problems with the engine bucking, not wanting to pass 3500rpm, and before all that I was having a weird hesitation that would act a lot like a rev limiter or fuel cut.. Definitely not the usual 3800rpm hesitation.

I tested the compression yesterday and all was healthy according to RotaryResurrection's website. It was 35psi per face and 105psi avg front and rear. I've also just recently replace both the high and low pressure fuel filters. The plugs, o2 sensor, and air filter are also fairly new with less then 1k miles on them and I've checked all the grounds including re-grounding the ECU. I've noted that the oil smells fairly strong of gasoline, but I have only flooded it once after encountering the weird hesitation for the first time. Otherwise I've not had any problems with it flooding. I've searched around and read the general consensus is that this is somewhat normal; I just figured it may be worth mentioning. My 5/6th ports were stuck and I was able to free up the rear actuator and sleeve, but the front sleeve is still stuck about half way open so I'm going to have to remove the intake to free it up. I tested the car out after fixing the rear actuator and sleeve and it only seemed like a minor improvement if any at all. I ran a resistance test on the CAS, BAC, and TPS and they all came back within range. I checked my Boost/Pressure Sensor for the pill in the line and it's still there and I checked the voltage to D terminal and it appears to be in spec for my altitude. So I figure my next thing to do was to check my timing.

I've removed the CAS and stabbed it on several occasions being sure to keep it in line and that the pulley was lined up. Once it's in all the way the slot is at the full advance position, or I can rotate the CAS a little further and try to insert it and it will end up in the full retard position of the slot. I reinstalled it at where it was at the full advance position and figured I'd see if adjustments needed to be made to it from there with the timing light or not.

I let the car warm up completely and idle was around the mid-800 range. I ran the timing light and ended up retarding the timing from where it was after initially stabbing it. But I could only get the yellow line to 'dance' around the peg. It would either be flashing right on it but jumping around slightly or it would go back advance past the peg and on a couple rare occasions I didn't see the line at all. I remember HAILERS saying in a topic to try flipping the inductor if wasn't flashing constantly but that did me no good. I had it positioned at the spark plug end of the wire and then moved it to the coil end. That didn't change anything either. I spoke with my dad who is a full time mechanic and he mentioned setting backup timing on a piston engine since the computer is always trying to advance or retard the timing by some amount. So I set the initial jumper and that didn't do anything either for the 'dancing'. I decided I'd try to check the L2 wire and no luck either, it was doing the same thing. I then went on to the T1 wire and it was reading perfectly on the red line. I tested T2 and the line was no where to be found on the pulley during the flash. I believe I've read the trailing coils fire at separate times somewhere so I just figure that explained me not seeing the red line while hooked to the T2..

I've searched around several topics but from what I've seen in all of them so far only HAILERS has come close to describing the problem I'm having and how to resolve it.

The entire reason I'm testing the timing is because when I was trying to pass emissions I had just moved it around on several occasions and never actually went back and set it correctly (still haven't passed emissions by the way, although last time I was pretty close).

Any ideas on what could be causing my hesitation problems and why my timing mark continually jumps around so much on the leading coil?

 

i had that same problem.
i took it to a mechanic and found out that i had a severe exhaust leak.
the gasket was blown to shreds.
he replaced it and then it ran beautifully

 

Hmmm..

I did have a giant exhaust leak between the two pre-cats until just the other day..
I could never get them to tighten up well enough so I removed the two and clamped them together solid and welded them up completely. Maybe I should grab another gasket for where the manifold and pre-cats bolt up and try re-tightening everything..

 

Any other ideas on these issues?

 

I think I'm having the same exact problem on my S5. It runs fine up until about 3000-3500 and then it hesitates, like a fuel cut off... It does it with or without load. I thought it was a fuel problem so I first checked all my fuel pressures, put a new filter in, and so on. I then tested all my sensors just like you. I have swapped the CAS and the Ignition Coil and still had a problem with no exhaust leak, btw. (Not sure how that would cause such a problem anyway) It's definitely not the 5/6 ports that are causing this, at least in my case.
It almost seems like the timing may not be advancing properly. It runs smooth up until about 3K like this {bahhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh} and then after 3K, usually before 3500 it all of a sudden starts going {bah..........bah...........bah.........bah....... ...} and won't want to increase rpm. When the throttle is released it stumbles all the way back to idle then runs fine and will accelerate smoothly back up until 3-3500 rpm and do the same thing.


Have you made any more progress towards diagnosing the problem? Anyone have any ideas?

Anyone have an S5 N/A ECU I could borrow just to rule that out?

 

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Sounds a bit like one of your secondary injector plugs is off. Easy to check on a non turbo car. Also while there, make sure one of the two wires on the secondary injectors has batt power on it with the key ON.

I've no idea on the timing of the original poster. The lead coil is a wasted spark system and both lead plugs fire at the same time. It might be a sparkplug wire problem. Like arcing to something or other. The timing is -5L and -5T at any speed below 1100 rpm. DURING start it's plus five for both.

Trails fire at different times, that's true.

I ususally put the inductor of the timing light close to the lead plug I'm looking at and make sure none of the trail wires is laying on it. If one of the two leads seems to fire intermittently on one of the lead wires, I just turn the timing light inductor opposite of the way it's on the wire when that happens. Then the timing light will flash consistently. Same place though, not jumping on either side of the pin.

 

Nope, I've still not managed to diagnose the problem.
It sounds like we both have similar problems though.

The hesitation went from being random to almost always at the same point like yours. The car will rev close to 4k RPM like normal, but once it gets there the RPMs just seem to oscillate up and down somewhat slowly. I popped the hood and revved the car up using the throttle linkage and it still did it. I disconnected the TPS just for the hell of attempting it and it still had the problem of not passing 4k RPM. I'll try to grab a video of it here shortly and post it so that everyone can see what I mean when I'm saying the RPMs are oscillating.

 

Here's the video of the hesitation taking place after letting the car warm up:

http://www.youtube.com/watch?v=m2R7Pbd0sw8

If I keep my foot to the floor it does just like you see in the video, the revs bounce and then start to turn into somewhat of a sputter, but as I let back off the pedal it finally revved past. I've tried to use this trick to get it to pass 4k RPM when driving down the road but it just wouldn't work at all when it was under load.

Are you talking about the electrical connections on the harness for the injectors?

I pulled both plugs and with the Igniton turned to ON I got close to a 12v reading on 1 from each pair. The reading seemed to fluctuate a little on the front injector but the rear injector seemed to give a steady reading.

I also looked through the FSM to see what it had to suggest about testing the secondary injectors (4-53 [4A-69 Online]). I couldn't distinguish any sound of the injectors firing from the rest of the noise coming through the flat head screwdriver (has a through metal handle so I figured it may work seeing as I don't have a sound scope). Then it mentions testing the crank angle sensor which I've already done. After that it goes on to say check the resistance of the solenoid resistor. The range is supposed to be 5-7ohms but mine is reading out 8ohms on all contact points. Could being out of range by 1 ohm be causing this issue? I also checked the resistance of the secondary injectors, but I forgot what number I came up with on the multimeter.

After doing all of this I just put everything back together and started it up again just to see if it'd continue giving me the same problem and now it seems to be gone. There still seems to be a slight lag when revving but it's no longer hesitating or sputtering. I drove it down the road and didn't have any problems either.

Here's a video of it revving after I finished all the testing:

http://www.youtube.com/watch?v=d4R8yWRhNb4

Also note the car almost shut off just briefly after the revs dropped back down; it used to do this every now and then but I've yet to figure that out either.

Any ideas?

 

I suggest your boost/pressue sensor is not getting vacuum and or the signal from it is not getting to the ECU.

In other words the ECU is seeing load even when there is no load. So look for vacuum at the sensor and the right voltage at the ECU for a engine with key ON, engine OFF. See FSM.

Also check and make sure the sensor has the right part number on it.

EDIT: OOPS. I see the car fixed itself. Disregard. Reseating the solenoid resistor might have helped. Got me.

 

So is the car doing it anymore? What part number is on your boost sensor? What number is on your ECU?

 

ECU - N326 18 881B
079700-1283

Boost Sensor - E1T12071
That was the only one I could make out for certain. I believe the ones above that read F027 and 5X07, but I can't be for sure.

I decided to try it out again today after letting it sit over night. The hesitation was back, but I noticed something going off of something I sort of noticed yesterday. If I don't hold the accelerator pedal to the floor and slowly rev the car up it didn't seem to hesitate until I got around 6K RPM.

I took apart the intake box ducting and checked the AFM just in case to see if anything was causing a restriction because I thought I heard some noise coming from it. Nothing to be seen. I reassembled everything and started pulling back the carpet to get to the ECU for the number. I had previously regrounded the ECU while trying to solve the common 3800rpm hesitation. I had used a stud coming up from the floor and put a nut on it to secure the eyelets. While I was there getting the number I figured I'd ground the eyelets out somewhere else instead just to see if it made a difference. I found a bolt running into the body in the kick panel area so I used it.

I put everything back into place and started the car up and took it down the street again. I know yesterday when the hesitation went away it revved to 8k fine but it seemed to be doing it somewhat slow still. Now it seems to actually be revving a lot more freely and without any hesitation. I'm wondering what the deal is..

Here's a video to compare how it's revving today vs the video I posted yesterday:
http://www.youtube.com/watch?v=u8hpdTzLXEE

The second rev I was doing it more slowly on purpose, so pay no attention to it when making a comparison.

 

if you have not already done so, add a few more grounds:

motor - chassis
battery - motor
ECU - frame

Next time it starts to act up again, grab a set of jumper cables. Attach one to motor and then ground on battery. Attach the other cable to motor and chassis.
Then rev it again and see...........

 

I'll have to keep that in mind.
I'm going to give it another try tomorrow and see if there is any change in how it runs.
Also my front auxiliary port is still frozen, so once I get the intake off and clean both of them up the car should run even better on the road. I'm hoping this issue was just caused by a poor ground location I chose for the ECU, but we shall see.

 

some poeple I have spoke to said it is over kill but I grounded my ECU to the frame, then grounded the ecu's frame/holder to frame as well. I figured if one ever was to not work the other would.
I also added a small ground to my tranny to chassis under neath, and most dont do that.

Well hope it works. We need more 7's running around here.

 

i had the same problem, id hit 3800rpms and it would be like hitting a brick wall. the problem is dirty secondary fuel injectors. just send them off the which hunter and they will send them back like new. only cost around $50. when they send them back they will send you a sheet telling the perfomance before the clean and after. on mine, one was only working at 33% capasity and the other wasnt working at all. when i got them back the car ran like a dream.

 

same here, i reground everything under the engine bay, and the ecu, went through 4 tps sensors, 2 boost sensors, regrounded all the sensors blah blah, i still dont know what it is. But mine never hesitated in neutral, only when im driving. I'm starting to think that its the injectors themselves or maybe the resistor box.

 

I took the car out to get some gas today and drove it around for about 10 miles. I drove it pretty hard and it didn't give me a single problem from start to finish. I may consider sending my injectors out for cleaning while I have everything pulled apart to clean up the 5/6th port sleeves.

 

Glad to hear your car is running better. Definitely get those port sleeves cleaned up and use a good shop vac to keep your engine clean before and during the process. You will notice an improvement, at least I did w/ my white S4.

My black s5 on the other hand is waiting for the arrival of a "new" ECU. After more searching on the forum I decided to check the ecu # and discovered that it is from a convertible. That caused me to be suspicious of the person I bought the car from. After some more searching I discovered that he had swapped the bad ecu out of his vert and into my gxl before I picked up the car. I also discovered that I inherited a bad CAS and TPS from his vert as well. Nice guy!

I already had diagnosed and replaced the CAS but still need to buy a TPS. As soon as I can get the ECU in the car my problem should hopefully be resolved. I'll keep you posted.

 

Well the ECU was definitely bad but it didn't solve the problem entirely. Unless I got another bad one there is something else going on. Now the hesitation (will not rev higher) starts between 4500-5000rpm. A while ago I checked my secondary injectors and could hear the solenoids firing, interestingly enough they come on around 4500-5000 rpm. It's possible they could be clogged so I think I'll send them out to be cleaned.

I also need to check my boost/pressure sensor as HAILERS suggested.

 

if your s5 OMP is bad and takes out your ecu dont plug up another ecu until you change the OMP or it could take that one out as well. Thats the only thing I hate about S5 is the stupid relationship between the two.

 

Ooo, that would suck, too late now! lol. Well I don't have any reason to believe the OMP is bad but I'll check anyway. The old ECU was water damaged and the boards were corroded inside which is why it needed to be replaced.