Hey guys, my 3.5ltr is seriously lagging under 3200RPM but once it hits 3200 LOOK OUT. i will be changing the plugs, leads and cleaning the air filter in 3 weeks but what one will be causing this? it dous have a small (tiny) miss on idle but ive put that down to a tiny hole in the exhaust? its near the rear of car just before very rear muffler! size of a match head! could it be this?

Recent increase in unsprung weight?

I doubt a hole in the exhaust would cause that sort of power loss or a miss on idle.

Recent increase in unsprung weight?



i have just put 20s on the car! did have 18s but it was the same before the wheels went on! other then that thats all...

My guess would be the 20s slowed it down a bit, exhaust hole wouldn't be it.

It's pretty normal for stock Magna's to be a bit ehhh until after 3k though.

Any increase in unsprung weight = higher rotational force to move it, so that would be sucking a bit of your acceleration.

Hehe. My new headers ironed out that flat spot a lot. <insert smiley face here>

I know the dead spot you're talking about. If its gotten gradually worse I'd give the car a once over (MAF, air cleaner, TB etc). If its happened all of a sudden I'd be looking for something obvious; something broken, or loose or missing.

Hehe. My new headers ironed out that flat spot a lot. <insert smiley face here>

I know the dead spot you're talking about. If its gotten gradually worse I'd give the car a once over (MAF, air cleaner, TB etc). If its happened all of a sudden I'd be looking for something obvious; something broken, or loose or missing.
yeah its been gradual! its like i can half throttle and it picks up ok but once it hits 3200 it just lifts sooooo much more! ive had 3x 3rd gens 2 2nd gens and 2 1st gens so im used to the "slight" gain at 3000rpm but this is bullsh!t how do i check MAF?

Someone in the past few days mentioned similar symptoms due to oxygen sensor?
[EDIT] 'twas spu100 in this thread (http://www.aussiemagna.com/forums/showthread.php?t=91005&p=1432501&viewfull=1#post1432501).

Cleaning the MAF and throttle body/idle circuit go hand in hand. No point doing one without the other.

The MAF is just behind the airfilter - has an electrical plug connected to it. I usually take it off completely and spray it a few times with contact cleaner, from both directions. While its drying I pop the ISC motor out and clean the throttle body. Then while that's clearing itself I give the inlet pipe between the MAF and TB a blast of cleaner. This way I know everything from the airfilter back to the TB is as clean as possible. I also clean the PCV while I'm doing all of this.

It sounds like a pain in the arse, but you may as well do the job properly. And you shouldn't really have to do it too often anyway. Every third oil change maybe, or when you notice your fuel economy going to sh!t.

In the old days, that was a clear sign of some valves not seating correctly. Might be a waste of time, but consider a compression test.

this is my 2 cents worth, my 96 te was doing similar things as well, would also occasionally be hard to start when cold or stall just after starting, so i did the 02 sensors then the injectors then the dizzy then the plugs and leads still no good then i replaced a 20c seal that sits under the air intake on the throttle body, i was told it acts a bit like an auto choke and when the seal go looses presure. fixed the problem tho

ive had similar problems, so far i have changed the fuel filter and air filter and decent improvement, hopefully it will be even better when i change the sparks and leads :)
Also could be your cat? i might be changing mine if the above doesnt do the job

Try replacing the fuel filter.

Eliminate the variables before splashing out big bucks on non-existent gremlins.

Put back on the old wheels and see if the issue is still there.

O2 sensor.
Gerry

Did you ever resolve this? Mines started bogging down stupidly when cold, and still a little bit when at temp :/

Electrics are fine - It's not trims as the ECU has been both reset, and flashed.

Vacuum is fine - It's just had an engine swap and is still doing the same thing, upper and lower intake gaskets were replaced, all vac lines checked and there are no TCL faults.

Intake is fine - Throttle body was cleaned out during the conversion, I made sure the plenum was clean. MAF was clean as well. We also replaced the breather hose to ensure no leak (old one had split)

Ignition has been eliminated - We checked your distributor, it was fine. Leads and plugs have now been done. Did it solve the miss?

Exhaust is not an issue - It was not overfueling, no leaks, I did not smell anything odd from your cat, and fuel eco was within spec.

Fuel is next imo - We reused your injectors, they may possibly need cleaning? Replace your fuel filter first, if there is no improvement when you come down we will try a spare set of injectors and see if there is any improvement.

---

Also, I've just looked at your video and noticed TCL engages... Can you turn TCL off and see if there is a noticable improvement in response below 3500rpm?

Thanks guys, I'll do fuel filter thisarvo, and turn tcl off, tcl won't effect I don't think as its the same through every gear! Yeah I'll most likely be down tomorrow arvo so I'll try injectors then if the filter is a no go!

And woob, sounds exactly the same! Try your fuel filter as everything else I've done has had no effect on this 1 issue,

Did you ever resolve this? Mines started bogging down stupidly when cold, and still a little bit when at temp :/

I'll let u know how I go tonight

O2 sensor symptoms.
Massive flat spot at low revs, driveability is so so when dead cold, In the warm up phase it is terrible. Feels like no throttle response at all up to over half throttle then the power comes in with a rush, I suspect that this will be a real handfull in the FWD models. Gets a bit better when fully warm.
Mid range exhaust drone is much worse. Fule consumption increase of around 10%.

The usual thing is that you know that something is wrong, cannot pinpoint why.
If you have access to a multimeter then an open circuit O2 sensor is relatively easy to check. Just look up in the manual.
Previous posts have described replacement options and their relative costs.

I suspect that the quickest way to get a new sensor is supercr*p auto. around $100.
As long as you have axle stands, a big wrench to remove the old sensor and a little commonsense to remove the passenger footwell carpet and the reinforcement underneath then this job should take about an hour in a driveway.
Gerry

Nope woob, I'll be doing injectors tomorrow and if that's no go I'll also be doing the O2, I'll keep u up to date champ

Ps: thanks spud, sounds like the exact symptoms!! Fingers crossed,

Bring that huge **** off jack with you and some stands, I think we have a spare o2 laying around (just incase injectors do nothing).

car is getting pretty bad pretty fast! im going to see how it drives to work and back and if its still "ok" ill drive it down with the trailer! if not ill bring monicas car and put everything in the back! (the reason i am telling this is because if i bring her car i wont bring the jack! but if i bring vr-x ill bring it!

Often this is actually the dist, have done so many now and have lost count

O2 sensor, highly doubt it as the engine takes no notice of the O2 sensor when cold, you have reset the ECU so initially then the base map would have been fine until the engine warmed up and the O2 sensor was then being read

Which engine is this with, was this an issue with the old motor, when did the issue start......

A lot of useless things have been done reading in previous posts in this thread, a lot of assumptions also made as well

Given has TCL, change the TB as well, have had a few where the actual TB was to blame, remember unlike non TCL throttle bodies that the throttle plate is not connected directly to the throttle cable, you can open by hand as many times as you want but unless you have a scope like mine, you will never see it when the car is in motion

Issue was around with the old engine, but conversion did not solve it. As for new gaskets etc... it was being done anyway - unrelated to this issue.

We also have spare distributors and throttle bodies to try out tomorrow night if needed.

Often this is actually the dist, have done so many now and have lost count

O2 sensor, highly doubt it as the engine takes no notice of the O2 sensor when cold, you have reset the ECU so initially then the base map would have been fine until the engine warmed up and the O2 sensor was then being read

Which engine is this with, was this an issue with the old motor, when did the issue start......

A lot of useless things have been done reading in previous posts in this thread, a lot of assumptions also made as well

Given has TCL, change the TB as well, have had a few where the actual TB was to blame, remember unlike non TCL throttle bodies that the throttle plate is not connected directly to the throttle cable, you can open by hand as many times as you want but unless you have a scope like mine, you will never see it when the car is in motion

started a month or 2 back, was with the 3.5ltr and now sticks around to piss me off with the 3.8ltr! yeah it may look like its a lot of useless things BUT at the same time i now have the 3.8ltr with new plugs,leads, fuel filter, timing belt, soon to be injectors and o2 sensor. so even if it does not eliminate the problem i still dont need to replace these things for a long time :D if they fail i will definitely try the TB and probebly the distributor also, ill keep ya posted on it anyways bud, thanks for your help.

Ummmm, why the hell did you use the 3.5 injectors for starters, that is astounding.....

Secondly, with the parts on the 3.8, clealy the old motor was not to blame as both do this, start with things that can acually cause this, personally I woudl start with dist, surely someone up there has a spare or 3, then if no go then move onto the TB

6G75 injectors were not available at the time, plus the ECU is expecting 275cc injectors with the Ralliart tune.

http://img580.imageshack.us/img580/2212/unledxvy.png (http://imageshack.us/photo/my-images/580/unledxvy.png/)

I know of atleast 2 other conversions that have been done in vic by an ex-mmal engineer that retained the 74 injectors.

Considering there's no difference in the flow rate between the injectors in the '74 & '75, of course you could use either. (Except the spray pattern is different.)

Considering there's no difference in the flow rate between the injectors in the '74 & '75, of course you could use either. (Except the spray pattern is different.)

Incorrect. 6G74 injectors are 275cc, 6G75 injectors are 305cc.

Come on, i liked it better when it was Surprisingly impressive or noteable! (Astounding)

Incorrect. 6G74 injectors are 275cc, 6G75 injectors are 305cc.

Incorrect. They flow the exact same. The spray pattern is the only difference.

If they flowed differently, would you be able to mix'n'match injectors on the same engine?

Incorrect. They flow the exact same. The spray pattern is the only difference.

If they flowed differently, would you be able to mix'n'match injectors on the same engine?

Want to check your part numbers and specs for me? ;)

CDH-275 for the 74 injectors
HDB305F for the 75 ones

Flow rates are reflected in the part numbers.

They both run fine, just the 75 ones run rich.

Incorrect. They flow the exact same. The spray pattern is the only difference.

If they flowed differently, would you be able to mix'n'match injectors on the same engine?

Thanks for that Al, some of us, those of us like yourself, DaveTJ and Me who have actually got experience in these things know what we are talking about, those who look up some random internet site will just read a line here and there and assume they know the answer, thus why assumption is called the mother of all **** ups

The 380 injectors do NOT have a different flow rate, either that OR every one I have ever had flow tested was really a 3.5 injector in drag.....

I Spose the bottom line is, this thread is asking advise on an unrelated issue as it was having the same drama with the "3.5 injectors in a "3.5 motor, I will sort out the 380 injectors when they arrive,

Start with the dist then and simple things like the MAF etc

Out of curioisity, did your motor not come with 380 injectors?

No but they are in the post!!! Funny story behind it all actualy, but Amc isn't the place for it :(

Spot on, after changing dist, injectors, tb, filter, plugs, leads maf, etc! It was o2 sensor
O2 sensor symptoms.
Massive flat spot at low revs, driveability is so so when dead cold, In the warm up phase it is terrible. Feels like no throttle response at all up to over half throttle then the power comes in with a rush, I suspect that this will be a real handfull in the FWD models. Gets a bit better when fully warm.
Mid range exhaust drone is much worse. Fule consumption increase of around 10%.

The usual thing is that you know that something is wrong, cannot pinpoint why.
If you have access to a multimeter then an open circuit O2 sensor is relatively easy to check. Just look up in the manual.
Previous posts have described replacement options and their relative costs.

I suspect that the quickest way to get a new sensor is supercr*p auto. around $100.
As long as you have axle stands, a big wrench to remove the old sensor and a little commonsense to remove the passenger footwell carpet and the reinforcement underneath then this job should take about an hour in a driveway.
Gerry

Well that was an interesting night...

Over the course of the night, the following was replaced:

- Distributor
- MAF sensor
- Injectors (now running the 305's)
- Throttle body and plenum (as per advice on faulty TCL TB's)
- Fuel pump (the sputtering threw us off)
- o2 sensor (This was replaced after a run with it unplugged to test as symptoms just didn't seem quite in line - esp with average fuel in the 11s)

Also note, o2 sensor issues will not trigger a CEL. Even unplugging it (causing a forced open-loop) will not give a CEL.

I am awesome!!
Please guys. The O2 sensor should be treated as a service item. They really only have a design life of 100,000, maybe they should be changed at the same time as the timing belt.
Gerry

I am awesome!!
Please guys. The O2 sensor should be treated as a service item. They really only have a design life of 100,000, maybe they should be changed at the same time as the timing belt.
Gerry
Yes sir you are

I have said this many times about it being a service item however unless the o2 sensor was a direct short, which is poss, I fail to see how this could cause no throttle response below 3500rms

More to the point, were any of these numerous items checked at any time, seems a lot of hardware chaged over with no testing done. Big waste of time and money there.

What did the o2 sensor come up in test, was the ECU registering any fault codes as well or was this not checked? An Oxy sensor will show up as being sluggish in most tests when checked. One last question, when left unplugged, was there any change in the way the car drove

- o2 sensor (This was replaced after a run with it unplugged to test as symptoms just didn't seem quite in line - esp with average fuel in the 11s)
Also note, o2 sensor issues will not trigger a CEL. Even unplugging it (causing a forced open-loop) will not give a CEL.Life, with a dead(ish) sensor, did you notice a difference when it was unplugged, or did it run the same? Just asking for future reference, as to what unplugging does/should result in. I assume(!) that if the sensor is OK, unplugging will show a marked difference in drive, whereas if it's buggered there won't be any difference?

Well basically mal I went and had life and Cary help me last night! They suggested injectors and dist because you seem to know your stuff! <-- not being a smart arse, this is seriouse. So 1st we changed dist, tested it. No change! So then it was time for maf, we cleaned all plugs etc and changed over maf, tested it, nothing! By the way YES we tested it after absolutely everything! One by one, anyways so you have seen the list, the only reason we changed sooo much before getting to o2 sensor was because you and alot of others had said not to bother, put it this way! Car used a full tank it 350-400km, when cold it would not move past 2000rpm towards the end. Unless I put my foot right to floor, even once warmed it would spit, cough and Carrie on untill 3200rpm but nothing as bad as when cold! As soon as we unplugged o2 it's performance increased 100% and once replaced (very last thing) it now runs like a rocket from idle to 7000rpm no lag/hesitation. I can't thank dean and Cary enough as there knowledge is the only reason the car is going soo well today! Dean may post the before video he took up, the vid was before the sensor was changed but after absolutely everything else was, I'm tired as shit so if anything seems rude or short, it's not ment to but hopefully you can learn from this? Cheers to you all for your help! I'm going to sleep

Only explaination for this will be the 02 sensor was a dead short, this can happen if the person who did your initial 3.5 change over did not unplug and remove the cable and chose to either hang the engine pipe off the cable or worse still, unscrewed the cable and twisted the wires. I have seen these in dead short before but did not give these symptoms, certainly is a first for me and will certainly have this in the back of my mind if I come across this sort of thing again in the future

Even though the o2 sensor will not bring up CEL, a quick plug in with a scan tool would have shown this up immediately, pity you did not have access to one before as this would have saved you and the guys many hours of mucking around lol

Is good is fixed now

Z.spender came down last night to pick up a few things and we fixed it it whilst he was here. The o2 problem was like nothing else i've experienced with o2 issues, thus it was last on the 'fix list'.
Distributor was the first item swapped out and then we continued eliminating other options. In the process we threw in the 6g75 injectors that were missing (through no fault of z.spender's) from the initial install and fitted a new throttlebody.
Once the o2 issue was fixed, smiles all round :)

The upside is that it didn't cost z.spender anything to fix and he was here for other reasons anyway, we just swapped known serviceable parts i had for his ones.
The other benefit was knowledge, another remedy stored in the ageing brain :)

The other benefit was knowledge, another remedy stored in the ageing brain :)

That's the bit that makes the effort worth while. That, and a car running properly.

Can you have a look at the O2 sensor that came off the car and check the above possibility, that the cable got twisted somewhere along the line and some of the wires are touching? Just out of interest . . . . . .

Something like this, maybe?

http://www.extreme-check-engine-light-codes.com/blog/testing_oxygen_sensor_heater_wires%20copy-1.jpg

http://img441.imageshack.us/img441/331/burnttoastxb2.jpg

Mal, only prob is that the car was great after the 3.5 was installed, ran great for a while then slowly started to go down hill. So it's not human fault. It cannot be blamed on labour. So somehow it is mechanical. I don't know how.