94-95 Q precat failure

[Q45tech]

Recently [last 6 months] we have seen 5 Q with melted precats.As best as we can tell, the root cause appears to be a failing fuel pump which under load [after running some period] cannot supply the needed pressure/volume..........resulting in a lean mixture which eventually melts one or more precats.

Speaking with drivers they remember a loss of power and just mashed the accelerator harder which made the power come up but the leaner mixture raised the heat.

Many continued to drive for some period [days, weeks, months]and only came in when the problem got so severe they couldn't drive the car.

Each exhaust manifold integrated precat cost $750 plus an equal amount of labor to replace. Compaed to a $400-$500 fuel pump.

No codes or MIL will set just the general sluggish feeling on acceleration..[light or heavy]......if the knock sensor check good you must test more things QUICKLY.

It appears thatb the 94-95 had a different catalyst/precat bed material from the 90-93.Not to say the 90-93 are immune, we just haven't seen the problem yet on those models.

[EWT]

Recently [last 6 months] we have seen 5 Q with melted precats.As best as we can tell, the root cause appears to be a failing fuel pump which under load [after running some period] cannot supply the needed pressure/volume..........resulting in a lean mixture which eventually melts one or more precats.

What kind of mileage did the cars have on them?

[Rex]

My dealer quoted me $1300 for pump and controller, figuring the controller isn't $800, where's a guy get that good of a deal on the pump? Or is that a DIY price?

[Q45tech]

The controllers never fail unless you abuse them by waiting to change the pump.

We change pumps all the time for $600....at least 2-3 per month sometimes per week.

http://www.infinitipartsusa.co...d=515

$235 wholesale plus shipping for the pump and 3.75 hours for exchange.....1 hour penalty surcharge if trunk is full of crap or the gas tank is full.

Burning out the controller is a $380/$500 plus another hour mistake.

Owner punishment for buying dirty gasoline!The factory told me they sample check these pumps for years and 250,000 mile equivalents.......yet they fail in half the time because of dirt!

Changing fuel filter every year is a good habit to get into.$50 a year vs [$600 pump plus $2,000 worth of injectors at risk].

[Rex]

Mine is making some buzzing sound, but it's barely audible (when sitting still) unless it's below 40 outside.

I got parts cost from my dealer for both around $315. I assumed the biggest "cost" was labor, which I'm not sure I'd want to try and tackle myself.

I use only BP 93 octane and never let the tank get down to 1/4 tank. I'll plan on getting the fuel filter changed this month.

[Jeff Williams]

Dennis, the precats are up by the engine, right? Are they connected to the exhaust manifold, or part of it?

[Q45tech]

The stainless steel tubular exhaust manifold and precats are welded together one piece non interchangable or obtainable separately! Each side is different!

Close coupled to light off fast in cool cold weather to reduce crankup during first 3-4 minutes of pollution before main cats get warm and start working ...........takes 10 minutes or when ever the coolant reaches 176F before everything is functioning well.

If O2 are fresh and fast switching. Weak O2 could contribute to problem.........but usually something else to melt them - a miss and heavy throttle or lean fuel...........too rich [for too long] or too lean either will do them in.

Obviously WOT is not maintained for much more than 30-50 seconds as 130-150 mph would be the result.

[Jesda]

Dennis, $400-$500, even $600 for a fuel pump? Wendle Infiniti has fuel pumps in stock for $315. Fuel pump installation labor was $50 for me for one hour.

And the fuel filter? $20 total for P&L.

And you can get fuel control modules for free (what I paid) on up to $100 on eBay or from a junkyard. As electronic components, theyre just as good as new ones, and quite simple to install yourself.

My goodness... if I was paying what other people are paying for the same upkeep, I'd buy a tricycle and call it good.

-Jesda

[Jeff Williams]

Dennis, in your experience, have you ever seen anyone remove the precats, or cut them out? If so, were there any performance change results, or repurcussions (other than enviromnental)? Do the Japanese engines have both precats and cats?

Don't misunderstand me, I am not considering this, I am just curious. I would think, if the car had the precats, it was because it would not meet emmission standards without them.

[AZhitman]

Good question - I'd be curious about this as well, considering there's no such thing as "cold" here.

[Q45tech]

The O2 sensor [or ecu interpretation] expects a certain tiny amount of back pressure from the precat just behind it.I have seen the long term block learn CHANGE when precats were gutted. I have never done one but have seen the results.The O2 makes the ecu think the exhaust is 5-10% leaner than it is so the ecu dumps 5-10% more fuel at cruise thus decreasing the MPG by 5-10% at highway speeds.

I believe the Japanese ecu are different to compensate for this.

Performancewise it is not significant and the risk of old cats needing the precats to pass emissions is great. Plus the error from the O2.

All the proper old Q I see show the long term block learn at 95-105% whereas I have seen some no precat cars at 120%.......lots of wasted fuel just heating the main cat up at least at cruise ..........never dynoed an emission legal vs an illegal.

I do my best to not touch or nor ever suggest [or think about] modifying emissions as I might be the unlucky one the EPA decided to prosecute. Fine is $10,000 [and maybe felony time/probation] per cat or precat or each emission device for someone who derives income from automobile industry.You'll find my Q oem to the letter.

Cold is relative, the cats need 600F to begin to work so I doubt you live where it is 600F even in summer. Reaction time efficiency is a function of temperature.........at idle old cats may not have enough left to work properly.........you should see the emission spikes when cars are stuck in traffic just idling.....cats getting colder and colder.

[Jeff Williams]

Good information, thanks Dennis. I have that luck, as well. Even though ALabama dosen't inspect their cars. I would happen to be the lucky one that got inspected, first. Anyone that shows up in a shop, with the cats removed, gets turned away for service.

I wish there was an easy way to test my pre-cats with 161,000 miles and 100,000 to go.

[elwesso]

Could this be the cause of my bad acceleration??? Is there any other signs of bad precats??? The fuel pump was changed within the last 6mo......

[sijoko]

If you gut the pre-cats, you will not pass the newer emission tests where the car is put on a dyno and subjected to a load.

Another problem with gutted pre-cats is increased noise. I am not talking about the good, performance noise. But rather, the annoying, rattling sound like something is loose.

The hollow pre-cat amplifies the valvetrain noises. Also, I would say that there is no performance advantage to the gutted cats.

[Jeff Williams]

I can testify to gutted cats being bad noisy. My friend gutted his cats on his 1986 Mustang GT, before he bought the SVO exhaust system, and it sounded terrible! I would not do that to my Q.

Sometimes, I like to just drive with the radio off, and enjoy the silence. Can't do that in an Honda, that's for sure.

I think I am an auto hypocondriac. Every time I hear about something that could go wrong, I wonder if my car is failing. I've been wondering about the cats, now, ever since Dennis posted this. If there is a test, I would be up to doing it, just to make myself feel better.

Along these lines, would replacing my O2 sensor make any difference in mileage or performance, if it seems to be O.K.? Or is this a fix on fail replacement item. Are there any other things that slowly rob the car of performance, or mileage?

[Q45tech]

The only experience I've had is my Q with Dinan ecu, stock exhaust, and intake against another Q wiith a Japanese take out engine where the installler didn't change the exhaust manifolds, had JWT ecu and loud exhaust and intake [hot air cone].

Rolling 55 mph Up to 130 mph it was give and take side by side losing and gaining half car lengths............learned all I wanted to know from that 25 second experiment.

Lots depending on shift points, my high miler [220k at the time seems to have more between 6,000 and 7,000 wheras the newer engine had more around 4,000-4,500.Should have been the opposite if the precats' backpressure was meaningful.

Guess the question is was the engine development work done with or without precats [since they knew they would sell 10 times more Presidents in US than Japan.

Above 4500 rpm the VVT decrease the valve overlap from 28 to 8 degrees seat to seat so one could assume there is NO exhaust reversion to dilute the incoming charge.The US and JDM cams are the same as are the headers [except for welded on precat].You can't control your overlap without changing the cams, but the effects caused by changing the back pressure are the same. When you reduce back pressure, it is equivalent to increasing valve overlap, and when you increase back pressure, it is the same as decreasing the amount of valve overlap.

As to precats/cats you just unscrew the O2 sensor and make an insulated hose attachment [metal] and metal for a few feet before heat resistant rubber to a zero to 10 psi gauge [taped to windshield] and measure the back pressure under idle, cruise, and high rpm load.........worse the higher you go.http://www.jdsdiagnostic.com/eptspage.h ... twork2.htm

Another thing is the EGR back pressure calibration without the precats the EGR amount may be insufficient to pass the NOX emission test [?]

http://www.installuniversity.c...e.htm

Some scientific testing shows that for for an exhaust system say from the O2 sensor back to only reduce power by 1% the system must flow 2.2 cfm at 20.4" H20.

"The tests came about because Kevin has developed a patented variable flow exhaust that uses a butterfly within the exhaust pipe. He initially expected to use the system to cause some back-pressure at low loads "to help torque". However, he soon changed his mind when any increase in back-pressure proved to decrease torque (and therefore power at those revs) on a properly tuned engine! What increasing the back-pressure does do is dramatically quieten the exhaust.

One of the engine dyno tests carried out by Kevin was on warm 351 4V Cleveland V8. Following the extractors, he fitted a huge exhaust that gave a measured zero back-pressure. Torque peaked at 423 ft-lb at 4700 rpm, with power a rousing 441hp at 6300 rpm. He then dialled-in 1.5 psi back-pressure. Note that very few exhausts are capable of delivering such a low back-pressure on a road car. Even with this small amount of back-pressure, peak torque dropped by 4 per cent and peak power by 5 per cent. He then changed the butterfly position to give 2.5 psi back-pressure. Torque and power decreased again, both dropping by 7 per cent over having zero back-pressure"

Now all we have to do is measure a stock good Q back pressure and define some limits as the old rule of thumb that a 3 psi back pressure is ok at at 2500 rpm cruise is obviously less than ideal.

http://www.asashop.org/autoinc/nov97/gas.htm

[maxnix]

One of the engine dyno tests carried out by Kevin was on warm 351 4V Cleveland V8. Following the extractors, he fitted a huge exhaust that gave a measured zero back-pressure. Torque peaked at 423 ft-lb at 4700 rpm, with power a rousing 441hp at 6300 rpm. http://www.asashop.org/autoinc/nov97/gas.htm

Note that peak torque rpm = 4700. Adding 1600 rpm = 6300 rpm which is peak horsepower, so that rule of thumb is confirmed for a 2 valve OHV engine.

I will have to read the article and see if the peak rpms for torque and horsepower dropped with increasing backpressure. Now if we just had a quad camshaft 4 valve V8 with VVT on the bench next to it for comparison.

[Q45tech]

Not all quotes correspond to web links some of the sites I use are subscriber only [pay sites and can't be linked] and sometimes I just stick related things in as I find them so as not to loose them.

I have over a million links on file unfortunately things and sites with good info disappear and go out of business.

[Jeff Williams]

Peak HP and Torque is one thing, but aren't we more concerned with the curve between, say 1800 RPM, and 4,000 RPM, where the Q really needs more torque?

[maxnix]

Peak HP and Torque is one thing, but aren't we more concerned with the curve between, say 1800 RPM, and 4,000 RPM, where the Q really needs more torque?

I would say more like between 750 rpm and 2800 rpm. It's cooking beyond that.__________________Brian1995 Q45 & Q45t

Discover the power of the button!