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Old 01-03-2007, 10:21 PM   #1
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Default Car is missing/surging/hesitating under higher boost

Let me start off by saying that any insight in my recent issue is appreciated and to thank members for your patience and kindness with your answers and opinions of my past questions. I just want to throw this out in a public forum to see if anyone else, by chance, has experienced anything like this so that I can be pointed in the right direction to troubleshoot my latest issue.

My 2002 FMII with a Hydra ECU has a sputtering, bogging, hesitating, surging, missing issue when I hit 9~10lbs of boost. Below that level, the car runs flawlessly. This happened coincidentally after I replaced my engine mounts to the stiffer Mazdaspeed units. The caveat is that I also replaced my plugs at the same time. One other thing I can think of is that I had a half tank of gas with a bottle of Chevron Techron Injector cleaner sitting for a couple of weeks while the car was on jack stands.

I realize there are three main things to troubleshoot, if I may over simplify here and they are air, fuel and spark.

This is what I have done so far to troubleshoot:

ē Itís not the plugs because I put back in the old ones that were fine to begin with Ė just wanted to start fresh.
ē Thinking it was a leaking BOV, went out and purchased a real Greddy RS BOV with the same results even with the BOV cranked full-hard.
ē Iíve since run two fresh tanks of gas so the Techron is not in the system anymore.

When I lifted the engine as far as I could go with a jack to remove and install the engine mounts, I did forget to loosen all the intercooler piping and a couple were pulled free of their clamps. Iíve since checked and re-checked the whole piping from the turbo, thru the intercooler, to the throttle body and there are no leaks so Iím confident that the air path is sealed.

So with the above stated, does anyone think that lifting the engine too far would cause damage to something that I should be aware of especially on the back of the head that I just canít see? Is it possible that replacing the plugs caused damage to my plug wires so that it runs fine until higher boost levels are reached? And my last question is could a half tank of Techron damage anything in the fuel system to cause the symptoms stated above?

Very sorry for the long post.

Dan
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Old 01-03-2007, 10:27 PM   #2
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It sounds like a fueling issue to me what does your wideband say, you might be flooding or even marginal on fuel at 9-10 psi, are you running the 550's? whoops i see you are letss hear the tale of the gauge
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Old 01-03-2007, 10:37 PM   #3
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It sounds like a fueling issue to me what does your wideband say, you might be flooding or even marginal on fuel at 9-10 psi, are you running the 550's? whoops i see you are letss hear the tale of the gauge
Yes 550's. I think my fuel is good?



You can see the RPMs going up and down here:



Here's one from September when it was running fine:


Last edited by Virus; 01-03-2007 at 10:47 PM.
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Old 01-03-2007, 10:45 PM   #4
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did you loosen any coil grounds or wires if you arent getting good reliable voltage it will not work properly. If that doesnt do it i dunno the af's look good and the advance doesnt drop off very dramatically or anything that i can see. A loose ground wire can **** up your world royal man.
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Old 01-03-2007, 10:51 PM   #5
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did you loosen any coil grounds or wires if you arent getting good reliable voltage it will not work properly. If that doesnt do it i dunno the af's look good and the advance doesnt drop off very dramatically or anything that i can see. A loose ground wire can **** up your world royal man.
True...true. I have those coil-on-plug deals on the 2002 head. No grounds. I'll be changing my fuel filter for the hell of it in the next couple of days to see if that has any effect.

*edit* Oh, other ground wires too...I have stared at everything in the engine bay looking for obvious things...I'll keep looking.

*edit* I changed the last sentence because it read too "smart-assy" and I didn't mean it too.

Last edited by Virus; 01-03-2007 at 11:17 PM.
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Old 01-04-2007, 12:07 AM   #6
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my friend added a bottle of injector cleanor once and it screwed his car up for a while,it wouldnt run right.
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Old 01-04-2007, 12:15 AM   #7
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my friend added a bottle of injector cleanor once and it screwed his car up for a while,it wouldnt run right.
Did it eventually clear up?
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Old 01-04-2007, 12:48 AM   #8
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Is it happening at exactly the same boost level indpendent of rpm? Does it improve past 10psi (if you're running more boost than that)?

Something that is repeatable like this is usually related to the electronics- like something with the hydra. The data plotted doesn't look unusual except for reporting the miss. Did you review all the data in the log to see if anything happens just prior to the miss?
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Old 01-04-2007, 07:54 AM   #9
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Is it happening at exactly the same boost level indpendent of rpm? Does it improve past 10psi (if you're running more boost than that)?

Something that is repeatable like this is usually related to the electronics- like something with the hydra. The data plotted doesn't look unusual except for reporting the miss. Did you review all the data in the log to see if anything happens just prior to the miss?
Does not improve past 10psi. It's starts at around 5K rpm...but I'll try it without hitting boost today to test. What kind of event would I look for in the logs?
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Old 01-04-2007, 08:58 AM   #10
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Does the '02 have the main ground strap off the back of the head? Make sure that didn't loosen when you pulled the engine up. Sounds like a bad ground to me too. Does the hydra have a dedicated ground that comes back through the firewall to the main ground point in the engine bay, or is it just ground at the ECU? Bad plug wire caused when pulling boots off of plugs. I used to have a spare set of wires lying around for troubleshooting. Try swapping wires with a local and see if it goes away.


Frank
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Old 01-04-2007, 09:58 AM   #11
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If it happens w/o boost then it's rpm oriented which is mostly likely standard electrical- like the grounds mentioned. When I left the engine to chassis ground off my 91 the ignition would rev much beyond 1500 under load. As for the other data points, just compare them to the "good" log as you did above. The key is to first look at the big picture and then work down to the areas that appear to have issues. - rob
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Old 01-04-2007, 10:41 AM   #12
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If it happens w/o boost then it's rpm oriented which is mostly likely standard electrical- like the grounds mentioned. When I left the engine to chassis ground off my 91 the ignition would rev much beyond 1500 under load. As for the other data points, just compare them to the "good" log as you did above. The key is to first look at the big picture and then work down to the areas that appear to have issues. - rob
Ran it up to redline without boost on the way into work this morning and it was fine. Ran it up part thottle with boost and it missed. I'll be checking for the ground strap after work this evening as I do recall a *snap* sound as I was raising the engine and thinking to myself "that didn't sound good". Figured it was the intercooler piping coming apart. This idea is peculiar though because the engine has multiple ground points. You guys are saying that even with one strap disconnected, such anomalies occur?
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Old 01-05-2007, 11:56 AM   #13
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Well,
My -91 Greddy developed issues in higher rpms and it was spark plug related.
The car was fine once below 6000 rpm and high boost and warm. In cold mornings it ran on 3 cylinders for few minutes until warmed up. Reason was contaminated connection between plug boot and plug. Regapping and cleaning wires got rid of both symptoms.
I think the spark found easier way to decharge through dirt than in pressurized cylinder.
So apart from grounds, check your coil-on-plugs for cracks and contamination as well as connectors to those coils.

hrk
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Old 01-05-2007, 12:24 PM   #14
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Well,
My -91 Greddy developed issues in higher rpms and it was spark plug related.
The car was fine once below 6000 rpm and high boost and warm. In cold mornings it ran on 3 cylinders for few minutes until warmed up. Reason was contaminated connection between plug boot and plug. Regapping and cleaning wires got rid of both symptoms.
I think the spark found easier way to decharge through dirt than in pressurized cylinder.
So apart from grounds, check your coil-on-plugs for cracks and contamination as well as connectors to those coils.

hrk
Thanks for the suggestions. I Ohm'd everything out according to the manual last night because I thought that I should verify that too. Everything within specs, clean, gapped.


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Old 01-05-2007, 12:27 PM   #15
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hrk is headed in the right direction- and it's simple to check. But if you're getting a miss under boost but not w/o, then it could very well be possible that your plugs are throwing a weak spark that's dying under boost. Given the fact that you've been tuning your car, you're plug(s) could very well be fouled.

Replace the plugs. When I was tuning my last race car I fouled plugs in just a short time of dyno tuning and they looked perfect.
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Old 01-05-2007, 12:32 PM   #16
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hrk is headed in the right direction- and it's simple to check. But if you're getting a miss under boost but not w/o, then it could very well be possible that your plugs are throwing a weak spark that's dying under boost. Given the fact that you've been tuning your car, you're plug(s) could very well be fouled.

Replace the plugs. When I was tuning my last race car I fouled plugs in just a short time of dyno tuning and they looked perfect.
I had a new set that I installed as stated in the original, looooong post. It did on the new plugs. That's why I was trying to go back to how it was...running fine with the old plugs. I'll throw them back in but it's not the plugs.
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Old 01-05-2007, 12:40 PM   #17
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my bad- did you check the gap? too big of a gap could cause it.

as mentioned plug wires too- I've had plug wires cause problems when they were in spec. Remember a lot of this stuff may be within spec for an NA environment, but that all changes when you add boost. Boost is a harsh environment for spark.
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Old 01-05-2007, 01:05 PM   #18
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my bad- did you check the gap? too big of a gap could cause it.

as mentioned plug wires too- I've had plug wires cause problems when they were in spec. Remember a lot of this stuff may be within spec for an NA environment, but that all changes when you add boost. Boost is a harsh environment for spark.
.030~.035 tried them both. Wires Ohm'd out at 1.9k for the short one and 2.5k for the long one. I'm going to get some new wires just in case i pulled on the wire incorrectly pulling them off the plugs. You guys are right, it "feels" and "sounds" like it on 3 cylinders and the spark is getting snuffed out.
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Old 01-05-2007, 01:06 PM   #19
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Does the '02 have the main ground strap off the back of the head? Make sure that didn't loosen when you pulled the engine up. Sounds like a bad ground to me too. Does the hydra have a dedicated ground that comes back through the firewall to the main ground point in the engine bay, or is it just ground at the ECU? Bad plug wire caused when pulling boots off of plugs. I used to have a spare set of wires lying around for troubleshooting. Try swapping wires with a local and see if it goes away.


Frank
Found the ground and it's there and has no resistance from block to chassis. I am going to follow your advice and go get some wires.
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Old 01-15-2007, 08:33 PM   #20
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FYI - It was the wires.
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