Engine bucking, hesitating and knocking... Grrr!

[sonnydas]

Hi everyone. Im new to this forum and was hoping someone could point me in the right direction. (Level of techincal expertise... 7/10)

I have a 93 SC400. it has 177K miles. In the last 3 weeks I have changed a leaky power steering pump and related vacuum hoses to manifold, rebuilt the alternator, changed all plugs and air filter. I tested all my plug wires with my multitester (resistance was within parameters as specified for OEM wires per lexls.coms website.) I have also checked the heater circuit resistance on all 4 O2 sensors (black wires) and were found to be at 6.3 K ohms as outlined in lexls.com...

The car has always... and even today... starts perfectly both hot and cold. But from standstill I get a lot of knocking/pinging and the car 'bucks' while driving. At idle when warm the engine RPM (under load) periodically drops below 500 and unless I tap on the throttle it wants to stall.

Until the power steering pump change 3 weeks ago... I have NEVER had issues with the car. Routine maintenance of course... but no issues that have stumped me. Until now.

Please advise! Thanks!

 

[KDog]

I would say you have knocked a connector out somewhere.
Probably a throttle position sensor (TPS) connector
or an ignitor connector.
or Airflow meter
Check all connectors in that area.

 

[Lambo]

hi Sunnydas, sounds like something may have happened to to vacumn lines that go to the power steer speed sensor, i have a Soarer, that i believe is the same as a sc400, the pump has a pressure switch, on the side of the switch is a small plasic tab the line directly behind the tab goes up to the front of the intake manifold, the other line goes to a pipe the comes out just under the water intake pipe on the front of the motor, maybe these have been crossed over , worth a look.
Best Regards
Lambo

 

[sideshow]

does it blow abit of smoke at start up

i have come across a faulty pressure switch on the power steering pump

it was puttin oil into m,anifold

maybe that migth cause it to ping oir run **** but i doubt it

just a thought

 

[sonnydas]

Wow! Thanks for the quick replies!!!

Firstly, thanks to those of you who replied! Much appreciated!

KDogI would say you have knocked a connector out somewhere.
Probably a throttle position sensor (TPS) connector
or an ignitor connector.
or Airflow meter
Check all connectors in that area.




Okay... I have tried to unplug and plug in all visible sensors to no avail. Same condition exists... I will remove, clean and reinstall both TPSs and throttle body today. Airflow meter: (Im assuming that's directly behind the air filter box) is clean and free of debris and when i remove the air filter and partially block the air stream with my hand the engine begins to stumble, so im assuming it may not be perfect... but the air flow meter is responding.


Ignitors appear to be dry and clean.

Lambohi Sunnydas, sounds like something may have happened to to vacumn lines that go to the power steer speed sensor, i have a Soarer, that i believe is the same as a sc400, the pump has a pressure switch, on the side of the switch is a small plasic tab the line directly behind the tab goes up to the front of the intake manifold, the other line goes to a pipe the comes out just under the water intake pipe on the front of the motor, maybe these have been crossed over , worth a look.
Best Regards
Lambo


Yes, the Soarer and SC400 appear to be the same... I checked the hoses to the PSP switch on the right side of the PSP. The vac hoses were loose, old and brittle... so i replaced both. I wasn't sure if I got the two reversed so i reversed them after a day of driving... to no avail. So i returned them to their original position.

Mind you... on my engine the first vac line goes to the front of the intake manifold... but the second goes to the large tube between the air flow sensor and the throttle body (???) Ive attached a pic with arrows to show what i mean... Did I screw up royally???

(Picture attached as attachment)

Regardless... the PSP works smoothly and without groans at all RPMs and speeds.

sideshowdoes it blow abit of smoke at start up

i have come across a faulty pressure switch on the power steering pump

it was puttin oil into m,anifold

maybe that migth cause it to ping oir run **** but i doubt it

just a thought

I checked the vacuum hose connection at the intake manifold and there doesnt appear to be any power steering fluid in the vac line or intake manifold... so im thinking maybe the swich isnt bad and leaking fluid from the pump to the manifold.

What about EGR valve, knock sensors, etc? Could any of these be malfunctioning? Are there any "immerse-in-hot-water-and-take-reading-type-tests" that I can do myself to see if they are operational, before I have to mortgage my home to take the car to the 'steal-er' ship???

Thanks again for all your replies! Much apppreciated guys!

 

[Lextreme II]

Test your TPS. We have instruction somewhere testing the TPS. PS vacuum lines are not important. U can run with it unplug. I would say double check the TPS with the referrence ohm values.

 

[sonnydas]

Testing TPS

Lex... thanks for your suggestion on the TPS.

I tried to find the testing/cleaning info on this site for the throttle body and TPS. Didnt have much luck. Any idea where I can get detailed instuctions?

Lexls.com shows good instructions on his site but I have 2 TPS's he shows only one on the throttle body... :-(

Also while I have the TPS and sub-TPS out... are there any resistance values I need to check for at the individual connectors?

Thanks again to everyone who's taken the time to help out!

 

[Lambo]

hi sunnydas ,
Looks from the pictire like the lines are in the correct place, sorry if i lead you astray with the line down under the water intake my engine is out of the car and the lines were taken off but not labled , my mistake, the small pipe below the water intake goes to the radiator Overflow bottle.
Best Regards
Lambo

 

[sonnydas]

Re: vac lines.

Cheers Lambo... just make sure you dont connect the vac line to the radiator overflow bottle when you get your engine back in.. LOL. Thanks for the help though.

Sonny

 

[Lextreme II]

http://www.lextreme.com/forums/showthread.php?t=2490&highlight=tps+ohm

 

[sonnydas]

So I removed the throttle body, cleaned it, checked the TPS's... put it all back together... and no luck.

Ive noticed the engine always stops when I turn it off at just part the '40' timing mark on the crankshaft pulley. Is this normal? I seem to remember it used to always stop at the '0'?

Is this what could be the problem? I havent (yet) messed with the timing belt. Is there some kind of vacuum retard or advance on the engine? If yes, is it adjustable?

Thanks for any help you can give me.

Pulling my hair out,
Sonny

 

[gloverman]

Hello

I seems likely that the problem is somewhere that you have worked. You have already rechecked the p/s and alternator side of things and the tps. I have seen where the spark jumps down the side of the sparkplug or out though the side of the insulator. The resistance of the lead will be fine. I suggest removing the sparkplugs and checking for small burn marks on the side of them. Also check for small burn marks at the bottom of the leads they are normally white and located just above the small rubber boot on bottom. Also check the condition of the rubber boot, they get a bit hard and sometimes there are small tracking lines inside them. This is where the spark leaks to ground on the sparkplug hex. This is why sometimes HT leads that look fine can be changed and the problem can be solved.
Also I persume you changed the alternator yourself. Is it correctly earthed and what is the output voltage? Have you done a voltage drop test on the engine?
Sorry I forgot - when you have your spark plugs out it might pay to check that TDC is correct and that your front pully has not delaminated. Checking the timing may help too. If it is incorrect then you need to find out why. Could be front pully or the TPS can also affect timing.
Cheers and I hope this helps.
Kelvin