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Help! 91 Ls400 Lack Power, Glowing Cats!


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Hi all,

My friend has 91 LS400 w/the 4.0 V8 w/180k and we can't figure this one out :cries: The symptoms are no engine codes thrown, lack of low end power, and the cats are glowing to the point of burning the excess oil and the engine bay is smoking ALOT! Also, acceleration from a stop results in a "put-put-put" sound from the exhaust. I've changed caps/rotors, spark plugs, spark plug wires, new, air filter, pcv valve, cleaned out TB, cleaned out EGR valve, replaced cats. The pickup is better, but the cats are still glowing when the engine is revved. What else can I do? Check timing? :( Any pointers are greatly appreciated! Thanks all...

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Hi all,

My friend has 91 LS400 w/the 4.0 V8 w/180k and we can't figure this one out :cries: The symptoms are no engine codes thrown, lack of low end power, and the cats are glowing to the point of burning the excess oil and the engine bay is smoking ALOT! Also, acceleration from a stop results in a "put-put-put" sound from the exhaust. I've changed caps/rotors, spark plugs, spark plug wires, new, air filter, pcv valve, cleaned out TB, cleaned out EGR valve, replaced cats. The pickup is better, but the cats are still glowing when the engine is revved. What else can I do? Check timing? :( Any pointers are greatly appreciated! Thanks all...

Cats are plugged/shot. Remove them and upgrade the exhaust while your at it, Or of course you could replace them. Good Luck :cheers:

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Hi all,

My friend has 91 LS400 w/the 4.0 V8 w/180k and we can't figure this one out :cries: The symptoms are no engine codes thrown, lack of low end power, and the cats are glowing to the point of burning the excess oil and the engine bay is smoking ALOT! Also, acceleration from a stop results in a "put-put-put" sound from the exhaust. I've changed caps/rotors, spark plugs, spark plug wires, new, air filter, pcv valve, cleaned out TB, cleaned out EGR valve, replaced cats. The pickup is better, but the cats are still glowing when the engine is revved. What else can I do? Check timing? :( Any pointers are greatly appreciated! Thanks all...

If I have read the post correctly he allready replaced the cats........ Why don'f folks read the complet post????

Sorry I have no thoughts on what to check. ?The red cats tell me there is unburned gas or oil getting into them, but I have no idea of why?

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Cats glow with engine revving.....

Catalytic converters do not glow in the short term, do you really mean Cats as in catalytic converter?

If you have already changed the catalytic converters then did you check for blockage downstream in the exhaust pipe? I have seen "cats" glow but only after long term use of the engine and that was the result of chunks of the catalyst honeycomb structure breaking off and blocking the exhaust flow.

The only other reason that comes to mind is an extremely RICH mixture, or unburned fuel reaching the catalyst.

And I don't see MAF, mass airflow sensor on your list...maybe....

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Wouldnt a faulty MAF sensor throw a code? Should I just clean it out with electrical cleaner? What would cause an EXTREMELY rich mix? Would faulty 02 sensors throw a code? When I took off the catalytic converters to replace them, I test drove it down the street and it still felt sluggish...

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Hi all,

My friend has 91 LS400 w/the 4.0 V8 w/180k and we can't figure this one out :cries: The symptoms are no engine codes thrown, lack of low end power, and the cats are glowing to the point of burning the excess oil and the engine bay is smoking ALOT! Also, acceleration from a stop results in a "put-put-put" sound from the exhaust. I've changed caps/rotors, spark plugs, spark plug wires, new, air filter, pcv valve, cleaned out TB, cleaned out EGR valve, replaced cats. The pickup is better, but the cats are still glowing when the engine is revved. What else can I do? Check timing? :( Any pointers are greatly appreciated! Thanks all...

If I have read the post correctly he allready replaced the cats........ Why don'f folks read the complet post????

Sorry I have no thoughts on what to check. ?The red cats tell me there is unburned gas or oil getting into them, but I have no idea of why?

It was a thought :blink:

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New cats could be faulty?! No way, I checked them before i welded them back in! I'm thinking its running WAAAY too rich because all the signs point to it...Fouled plugs, glowing *NEW* catalytic converters, fuelly smell from exhaust, feels like its choking upon acceleration...Soo, with that said- what do you guys think it could be? There are no engine codes thrown ;[ Dirty MAF? Faulty 02 sensors (even though there are no codes thrown)?? I'm runnin out of options fast! lol Thanks again for all the pointers guys!!!! :rockon:

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Glowing cats = excessive fuel. No codes = something other than a monitored sensor or other device at fault.

My guess, the T-belt has jumped and the cam timing is off.

But that's just a guess from this distance.

Stop replacing parts and diagnose the thing.

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Have a muffler shop test for back persure. It could be a muffler and not a cat. Around here it is a $15.00 to $20.00 test. I would also check the timing. Then??????

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"putt putt putt" sound makes me think one or more of the cylinders are not firing properly so timing check as previously suggested would be a good thing to do. Also, have you rechecked plugs since all these parts were installed to see if they are still fouling? :geek: If all are, then i would think definitely timing related. If only one or two are fouled, could be a stuck injector (or valve problem).

Was the glowing cats and lack of power the initial problem that prompted all these parts being replaced, or was there another issue that started this journey? Just curious, there may be some relationship.

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Yep, the glowing cats heating up the oily undercarraige to SMOKE and the lack of power prompted all the parts being replaced. The parts were all original and worn. I have no idea how the engine even started, let alone ran lol. It idles just fine at about 650 rpms.It only put put puts when you stomp on the go pedal...Doesnt really go anywhere. I cleaned te MAF sensor out, still the same...Like I said before, I drove down the streets with the exhaust "unhooked" and it still felt sluggish. The new plugs have no more than 5 miles on them...Good points all, so how do I go about checking the timing? I have the gun, but the 2 dizzys are new to me...

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Well, I deduced that since the car performed the same when the exhaust was "unhooked" as opposed to it being hooked up, it could not be a plugged exhaust system. I wish it really was!!! :chairshot: If the computer was malfunctioning, wouldnt it throw an engine code? Anyone know how to reset/check timing on this thing??? Thanks!

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FROM THE OTHER THREAD:

Hi J-roc,

You can check the timing with a standard strobe light. You have to connect the diagnostic terminals TE1 to E1 together which disables the throttle position sensor and puts the ECU in idle mode. You then hook the strobe onto the lead going to cylinder 6 (found under the cover going from the left bank to the right bank at the front of the engine) and set it to four cylinder setting. You should see the timing mark on the crank aligned with the 10 degree before top dead centre mark on the block. I have yet to do this but for thats what the manual for my 92 says. I am going to post a tutorial of this on Lexls site as soon as the weather gets warmer!!

Cheers,

Leadfoot.

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Can you elaborate more on the "four cylinder setting?" How does one go about accomplishing this? Also, if the timing is off, how do you adjust it? I know its not like an American V8 where you just unloosen the dizzy and turn it accordingly...Thanks!

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Just an update...the problem was fixed!!! :chairshot: Drivers side coil went out :wacko: It idled smooth, but it felt like it was running on 4 cyl (it actually was! :censored: ) Since it had 2 dizzys and no trouble codes thrown, I had a bear of a time trying to diagnose it (I've grown accustomed to the 1 dizzy) I was very surprised that the code for a misfire wasnt thrown...Then again we're talkin about the basic OBD. Anyways, now it runs like a top, especially after the extensive cleaning/replacement of all the worn parts. Hopefully the trans can handle the new power lol Thanks you all for your help!

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Can you elaborate more on the "four cylinder setting?" How does one go about accomplishing this? Also, if the timing is off, how do you adjust it? I know its not like an American V8 where you just unloosen the dizzy and turn it accordingly...Thanks!

Glad to hear your trouble is sorted out.

The "four cylinder setting" is for the timing light. Doesn't matter if the light fires on number one cylinder or number 6 (1-8-4-3-6-5-7-2) as the timing mark is in the same position, and the timing is unadjustable as far as I know (ECU does it all). You just check it to make sure its working within spec.

:cheers:

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Just an update...the problem was fixed!!! :chairshot: Drivers side coil went out :wacko: It idled smooth, but it felt like it was running on 4 cyl (it actually was! :censored: ) Since it had 2 dizzys and no trouble codes thrown, I had a bear of a time trying to diagnose it (I've grown accustomed to the 1 dizzy)

J-Roc how did you find that coil is dead ? Did you perform any test procedure ? Thank you.

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J-Roc how did you find that coil is dead ? Did you perform any test procedure ? Thank you.

The workshop manual for the 92's state

Ignition coil service specs;

Primary coil resistance (Cold) 0.3–0.6 Ohms from –10 to +40°C (14–104°F)

Secondary coil resistance (Cold) 9–15 kOhms from –10 to +40°C (14–104°F)

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The workshop manual for the 92's state

Ignition coil service specs;

Primary coil resistance (Cold) 0.3–0.6 Ohms from –10 to +40°C (14–104°F)

Secondary coil resistance (Cold) 9–15 kOhms from –10 to +40°C (14–104°F)

Have you any picture/pdf how to check this ? I don't know which pins are for primary, which for secondary.

Thanks for answer...

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Another guess from over the pond, a pal of mine had a Ford that would idle perfectlly but would not drive

at all. Problem was low fuel line pressure, new fuel pump fixed it.

If you think it's flooding with fuel, have you checked the injectors?

cheers

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  • 2 months later...

Just an update...the problem was fixed!!! :chairshot: Drivers side coil went out :wacko: It idled smooth, but it felt like it was running on 4 cyl (it actually was! :censored: ) Since it had 2 dizzys and no trouble codes thrown, I had a bear of a time trying to diagnose it (I've grown accustomed to the 1 dizzy) I was very surprised that the code for a misfire wasnt thrown...Then again we're talkin about the basic OBD. Anyways, now it runs like a top, especially after the extensive cleaning/replacement of all the worn parts. Hopefully the trans can handle the new power lol Thanks you all for your help!

Big Thanks guys... my dad's LS was doing the same thing, changed the plug wires and that didn't resolve the issue... i came on the forum and read up on this and exact same problem. The coil was bad. :cheers:

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Hi all,

My friend has 91 LS400 w/the 4.0 V8 w/180k and we can't figure this one out :cries: The symptoms are no engine codes thrown, lack of low end power, and the cats are glowing to the point of burning the excess oil and the engine bay is smoking ALOT! Also, acceleration from a stop results in a "put-put-put" sound from the exhaust. I've changed caps/rotors, spark plugs, spark plug wires, new, air filter, pcv valve, cleaned out TB, cleaned out EGR valve, replaced cats. The pickup is better, but the cats are still glowing when the engine is revved. What else can I do? Check timing? :( Any pointers are greatly appreciated! Thanks all...

First, let me say that if the ECU was bad, since it is what throws the codes, its likely there would be no codes displayed if the ECU is indeed the culprit.

there are several things that can cause cats to glow red, and all of them include the engine running rich.

the reason why the cats glow red is because there is fuel inginting inside them. if those cats werent there you would be shooting flames from your tailpipe more than likely.

because your car is doing this, the new cats you put in, are blown again. i would check the timing,a nd i would also check the injectors. Also check the coils. before moving on to the most expensive option...the ECU. replace the 02 sensors NOW though, cause alot of times, esepcailly on OBD 1 cars, they are bad and do not throw codes.

EDIT: oops, old thread...my bad, didnt read the whole thing before i replied, glad you got it fixed tho...

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