SuperK's Mystery ZE: Troubleshooting the VAF? And TPS!

[SuperK]

Hmm.... I just can't seem to figure the ZE out. It's a mystery beyond mysteries.

If anyone remembers, I have Gro Harlem's ZE MX-3. It worked great for a couple months, now it's got me completely stumped.

The car is idling fine and is drivable... however, there seem to be "dead spots" in the throttle. These spots vary, but are most noticable on common highway speeds.

For example, if I'm going 75 stable, the car will completely lose throttle down to 70, then "buck" back up to 75 and continue this vicious cycle.

I can, however, while going 75, give it some juice, in which it hesitates for a split second, buck, then kick back with it's ol' ZE fury. Let's say the ride isn't very pleasant. Especially with completely shot engine mounts and balljoints, a bad cv axle, and control arm bushings.

For the record, the car's got replaced:
Rebuilt Injectors
FPR
Timing belt/tensioner
O2 sensors
vacuum hoses
Spark plugs/wires
HEI mod and blaster 2 coil
Replaced disty cap and rotor
replaced ignition module
Grounds checked/cleaned
TPS
Fuel Filter


And believe me, it's GOT fuel pressure!

FUEL PRESSURE!!!




So in accordance to "SuperK's Guide to Fixing Cars Like Certified Mechanics Do", I am continuing my journey of randomly replacing items that could be wrong and wondering if it'll fix it for at least long enough for the driver to get halfway home.


I did find this topic, which was particularly interesting to me:
http://www.mx-3.com/phpBB3/viewtopic.ph ... af#p380535" onclick="window.open(this.href);return false;


So I thought, hey! How about checking my VAF?
... And I read that thread... and realized SuperK is after all, partially retarded, partially awesome (which levels SuperK out to be quite average)
And I couldn't figure out exactly what I'm doing... or how to do it right. I have a digital voltmeter, and a set of screwdrivers, sockets and hands.

Can anyone walk me through testing my VAF? I pulled it off today while replacing the filter and noticed it... jingles? If anyone cares, I can remove it and record "jingle bells" by shaking it in front of a microphone, if that will entertain you. I... don't think that would cause an issue...

[94drumx3]

wow...not to be off topic again...but thats an awesome picture!!

[mazdanut08]

My car did this at low rpms when my TPS was messed up I see you said you replaced it and all but I had to turn mine all the back towards the windshield for it to not do any bucking or weird revs when I would rev and be easy on the gas It would drop and go back and forth really quick if I held the gas in certain places. But the VAF Ive heard try tapping on it with a screwdriver or something at idle and if it affects the idle it needs to be cleaned or replaced.

[Mooneggs]

when I had your symptoms it ended up being related to my injectors and HEI mod...

I've got a spare JE50 that I might be willing to sell...

[shameem]

VAF Ive heard try tapping on it with a screwdriver or something at idle and if it affects the idle it needs to be cleaned or replaced.

+1

Also you probably replaced the TPS with a j/y piece (considering a new one is like 200 bucks) - which means it is more than likely to be a bad part......

This might sound mundane and redundant - but check for air hose leaks - spray some carb cleaner (or some other flammable gas if you are feeling adventurous) around the intake and vacuum hoses and see if that affects idle...

Did you disable (remove) the stock ignitor for the HEI mod?

[SuperK]

The HEI mod was done before I got the car by Gro Harlem.

He was the one that wrote up the how-to FAQ on... how to install the HEI mod.

Therefore I trust he modded it successfully. I just re-replaced some parts since I got it, since things looked kind of shabby.


I got the replacement TPS from Kirk95gs. He said it worked fine...

I haven't set it properly just yet... in fact... one time it completely refused to let the car run AT ALL so I disconnected the TPS completely and the car drove home erm... not very fine. It was rather a very unpleasant ride, but it made it home.

I have already sprayed and checked for leaks. It's sealed up very well...

[shameem]

Look into the VAF first, TPS next and then check the HEI mod (just to be sure) - you can check TPS with a multimeter making sure there are no dead spots or funky readings (its basically a potentiometer).

Also i was just reading through your battery rant - a bad battery/alternator/electrical system can and will unleash all the gremlins in your engine system.....

[SuperK]

Well, all the recent testing is done with the good Orbital battery, not the Floptima.

again, I am not sure what I'm looking for on the readings. This is where i need the help. I am going to guess this goes for both the VAF and the TPS.

I have a digital multimeter. This could be the beginning of my mistake, do I need an analog one? (or an analogue one!) Or can it be done reliably with a digital one?

I have played around with the TPS and the multimeter. Am I looking at voltage or ohms? I know the TPS isn't linear, so it shouldn't be the same reading, but off the top of my head, the ohms read somewhere like .175 - .195 or something such. Voltage is the same... but this is like telling me to read greek. Sure I see the characters... but exactly what do they say?

I noticed though, while setting the TPS, there's a spot on the low end, if I hit it stable at 1.5k RPM, the idle bounces 1-1.5k. I raised the TPS slightly until it subsided... I can't test the high end because I don't have tags so the car is kinda in "house arrest" which means I'm stuck in the parking lot.

I also knocked the VAF with a sledgescrewdriver and it didn't do anything... meh?

[shameem]

http://www.mx-3.com/manuals/showimg.php ... F2-150.gif" onclick="window.open(this.href);return false;

[SuperK]

As I understand it, it shouldn't be linear continuity, correct?

That makes it just about impossible to test without an analog (analogue) multimeter... I guess I should snag one of those before continuing. Unless I am misunderstanding something.

[SuperK]

Here's the weird part of this issue...

I adjusted the TPS so it works smoothly, right?
So the car's been working nice and smoothly last night, and on half of my trip today...


but after 50 miles of driving, it starts it's whole loosing power shenanigans again. ...

[shameem]

Look into the coolant temperature sensor that goes to the ECU (possibly change it - they are cheap) and burp the cooling system (run the engine with the radiator cap open and the heater (and fan) on full until all the air bubbles are out).

If you have a known good disty - you might want to plug it in - that will rule out any disty problems....

You can also try sticking in a k8 ECU to see if there are any codes (other than EGR)

Also be aware that heat could upset any fine adjustments to the TPS - i had an experience where after driving for few days the bolts holding the TPS would come loose..... i had to get a new set of bolts and put some loctite on them....

[SuperK]

I did run a compression test, I finally bought the darned part.

It's running just about dead on 180 on all cylinders except 1. cyl. 1 is about 160-ish.


I tested the ignition spark, every cylinder is delivering spark... the coil pack (msd blaster2) is delivering steady 40k volts, I didn't exactly check it at 45k...

and every cylinder is receiving spark as well. However, it's a lot weaker, stable at about 25k at the plug.

I did notice something odd. every about 10-15th spark from the pack and it seems like it "misses." I don't know if that's an issue or not. Just goes "pack pack pack psst pack pack" and it's not extremely noticable, and I don't know if it's because I'm cranking the engine or even if it is an issue, but it's something to note, I suppose.


But the part I don't understand is... It cranks instantly (well, not as instant as my 4 banger. Sucker turns once and it's on) and it idles for about two seconds very smoothly and dies. I tried this over and over. It's the same result with the TPS and VAF disconnected as it is connected. Giving it throttle will instantly kill the engine, whether it's a tap or to the floor. Same issue with TPS and VAF disconnected or connected.

Seriously, am I missing something here? with my "bleeding arse" experience, I think it's safe to assume I'm getting PLENTY of fuel pressure, but I guess I could get a gauge and hook that up just to verify...


erm... so if I'm getting fuel, and getting spark to the cylinder, what's missing?


I haven't done the coolant sensor replacement yet... I don't mind doing so, since it's cheap and easy... but I can't run the engine to clear out the bubbles anyways... I am not sure how this would cause the issue, though.

ECU? CAS? What should I be looking at now? I hate working on this thing in the parking lot

[shameem]

If you can get a j/y disty or borrow a good one from someone - then try it - that will eliminate any issues with the disty or HEI mod.
If both spark and gas are there and you got good compression - then it would be ignition timing...

If CAS is an issue you may have trouble starting the engine - but it still doesnt hurt to check it.....

Honestly - the idling and 'dying if given gas' sounds like a huge vacuum leak or injector failure (all injectors are plugged in to the proper plugs right?)

The easiest way to go from here is to pull codes with a k8 ecu.....

[SuperK]

Hey, I got a digicam recently.


Let me know what your suggestions are on the issue:

here's kinda what the bay looks like, I guess:


Everything plugged in, started:



do note that the only way to keep the car going is to "flutter" the throttle. The farthest I was able to rev the engine was about 3k this way. Give it too much gas and the car dies instantly.


VAF unplugged:




VAF unplugged again:





"I like dragonflies":