V8 Mileage 4 Cylinder power

[gabe]

Couldnt believe my mom was letting me take her brand new 98 Q45 down to New Orleans with 3 friends. As a brand new car I remember thinking duing our trip that this car is alot more sluggish than I would expect from high end japanese luxury car.

Back in October of 03 I ended up offering my mom money for the car than the dealer would on a trade in for a new 2004 Q45. I knew how well maintained it was. Low miles and driven like a pontoon boat. (slow)

Fast forward to now. I put some 18's on it with 245 40's which lets me corner better and really all I want to do is speed it up a bit. I dont think its running poorly because there arent any warning lights on the dash but it does feel like it running on less that 8 cylinders. I would really be racking my brain if it werent for the fact that I knew it wasnt very fast brand new.

So If I gotta pay for a V8 I want the performance to match.

ECU upgrade?Replace Exhaust?What else is safe?

[DAEDALUS]

Everyone has their own opinion as to what "fast" is. Most people on here wouldn't call a '98 sluggish, but performance did suffer in that generation. That said, there is no reason why it can't be about as fast as it was when brand new...not sure if it is or not from your post. How many miles on the car?

Welcome to NICO!

[gabe]

Thanks for the welcoming just found this site today but have been searching for info for a long time.

Im just looking some respectable acceleration for city driving.

I have seen stock numbers 0-60 7.7 seconds. I dont feel like its hitting that mark. I had a 99 Lumina with the 200 HP 3.8L V6 and its 0-60 time was listed about the same 7.7-7.9 seconds but that car felt alot faster all the way up to 60mph.

My Q45 has 72,000 mi. Just put in a new air filter and other than the wheels everything is stock.

Im an ex-delivery driver so I like spirited driving but Im not looking to do any burnouts go drifting in it. I just want to be able to outrun the V-6 sitting next to me at the light. Right now the car just limps off the line no matter how far I depress the accelerator.

Any helpful performance ideas would be welcome. So far Ive seen a ECU upgrade from Jet Chip for around $500 then Ive heard of replacing the exhaust with a more free flowing one. Cost? Ive looked into superchargers but the $ threshold stopped me in my search for that.

Lastly I would like to mention that sometimes the car does seem to perform better off the line than at other times. Not sure if humidity or temperature are to blame. Cant really verify a pattern. But if I could get the car to at least give me stock acceleration numbers consistently Id be happy.

[greg_atlanta]

The rims are slowing you down a little.... but not a big difference.

Don't assume it's been perfectly maintained. Has the 60K service been done? Consider an intake cleaning and an injector cleaning. Fuel pump may be weak. You need to focus on proactive maintenance first.

[PalmerWMD]

In addition to checking stuff like sparkplugs:

If it has never seen a cleaning of the complete intake system and has always been driven slowly the intake is cure to be full of crud all over.

You likely also have tons of deposits in the combustion chambers.

This will make you slower , PLUS it may make for summer knock (cuz those deposits can change compression AND serve as a source of pre-ignition).In that case, the ECU would take out a lot of power, to protect engine.

The above 2 are huge sources of power loss and usually overlooked, even many by dealer techs.

Fred..

[Q45tech]

7.7 seconds seems fast to me, more like 8.0 seconds and 8.2 in summer heat. from the few I have stop watched.Spark plugs, clean throttle body, and plenum runner passages.......the jet chip won't accomplish anything on the 98 Q and neither will anything else but extremely loud exhaust then 0.1 second improvement at best.

Each 11F above 60F ambient drops power by 1%.Are you using ethanolized fuel in Illinois that's good for a 3% power drop alone.

What it is is what it is.

[elwesso]

I think you should take it to a dealer and just have them compile a list of stuff to replace..... We can tell you whats important...

I might try decarbing a little and driving the car harder..... Surprisingly enough (and I love it), the harder you dirve these cars the better they run!!! The VH doesnt like to be pontooned around!!!

[Jesda]

This is especially true on the Cadillac Northstar V8 engines, where many elderly owners baby them thinking theyre being good to their car, when in reality theyre contributing to carbon buildup.

Then, the dealer lowballs the trade-in on a new Seville or Deville, while the elderly man or woman buys a new one thinking the previous had an engine problem.

The dealer then performs procedures to clean out carbon deposits or takes the vehicle on a few aggressive wide-open-throttle runs, and the engine problem is solved. The vehicle is ready for resale or auctioning at a hefty markup.

-Jesda

[Checkered-Member]

My friends' dad has a daily driven 2003 C5 Corvette 31,000 miles, and he drives it so slow and so mild with it, that at exactly 30K the battery & alternator went out and all the piston rings were weak, engine had to be rebuild (all under warranty) when they opened the engine up the carbon build up was disturbing. (in 4 weeks his getting a C6 btw)

I had my car for about 50,000 miles and I drive the piss out of it everyday, redline every red and stop, and still running very strong, 0 problems…

Well Maintained = Well Driven

[gabe]

Thanks for everyones input. I will look into the service history and also try some simple over the counter intake system cleaners.

Ive read in other posts how the ECU retards engine timing if engine knock is discovered. This sounds like the most reasonable explaination so far. Tell me though if my symptoms match this diagnosis. Sometimes, not always, the car performs strongly when its been cold for hours or right after a fillup. Performance seems to drop all at once not incrementally at some point within 15 minutes of driving.

[PalmerWMD]

Car performs well when its cold (more than the usual improvement that all cars see) and poorly when warm is consistent with 2 things in my mind :

-Summer knock with subsequent retardationOR-Cooling system inefficient for one reason or another (for example radior clogged , not flushed ever,.. or filled with partial fill of tap water, which wouldhave promoted clogging), and the subsequent higher temps seen by ECU, would result in switching to a different map for running the engine.

Dennis has mentioned the exact temps at which this occurs on these pages a couple of times.

It is progressive, the warmer the coolant gets, in steps, the ECU will retard power, to protect engine.

Fred..

[elwesso]

I agree with Fred....

I think you should check the timing to be sure... Check when hot, hot-ish, and so on.....

Sounds like you need to catch up on some preventative maintenace anyway!!!

The ECU goes into retard mode at 194.9999*F... It will retard timing 1 degree for every 5F above 195, at a maximum of 5 degrees of overheat retard...

So at 220 its maxxed out, and after that the car will start acting REALLY goofy, as it has no idea what to do...

However, all the above assumes the Y33 ECU is set up the same way as the G50, which I would assume it would be similar...

[Q45tech]

Every make and brand has a over temp coolant retard table........most ecu work the same way as to things they monitor and how they react.As an engine is an engine.

Easy to guess where the reduction starts as most use the point [or just above the point] where the thermostat is 100% fully open.

195F in the case of 90-96 Nissans, some late models like G35 use 200F with the new open deck design.

Why so important to learn these things as applicable to all gasoline engines.

Study some of these Ford look up tables:http://www.eec-tuner.com/biz_h...s.rtf

[duck3986]

I have a '98 with 92k miles and have experienced problems similar to what you describe this summer.

It will run especially sluggish when it's over 80 degrees and humid. Sometimes, especially when cooler, it runs great.

I have no check engine light. I've replaced fuel filter, plugs, MAF, intake temp sensor and pcv valves and run BK44. She idles beatifully.

When the rpm get above 3,000, power comes on stronger and smoothly.

I'm guessing i have the carbon issue and/or back knock sensors. I'll have to pull the plenum sometime soon.

If you find a solution that works for you, please let me know. I'll do the same.

Don

[Q45tech]

Compare AC on with AC off [not just turning it off a minute earlier but never turning it on after the Q is cranked. This avoids the AC data flag set in ecu and then you only have real air density, coolant temp and the ambient air temp signals to adjust the ecu.

90F ambient on highway [with stock air filter system] should be no higher than 110F real air in TB compared to 60F.........5% should not be feelable [- 15 HP].

On the highway it takes about 0.3 second longer to accelerate from 50-80 mph.

Common for coolant to rise 20F from stabilized 182-184F in traffic without the interior gauge moving any amount........the AC condenser output air is 30F hotter than ambient. A marginal radiator get overwhelmed quickly.

[gabe]

I will definitely reply if I find a solution Don.

coincidentally I ran into a guy this week that has a 99 Q45. I asked him if he was happy with his cars performance. He said "No and its a gas guzzler."

Sounds like a pretty common complaint with this version of the Q.

[PalmerWMD]

I suspect his maintenance can do with some catching up.

A 99 Q45 is some of the lowest fuel consumption for a V8 luxury sedan out there..

Fred..

[maxnix]

coincidentally I ran into a guy this week that has a 99 Q45. I asked him if he was happy with his cars performance. He said "No and its a gas guzzler."

Sounds like a pretty common complaint with this version of the Q.

Definitely not. The real world economy is not much better than a G50, but neither is the perfrmance much worse.

Such questions need to be prefaced with questions about maintenance and driving style and driving environment for the answers to be meaningful.
Modified by maxnix at 9:58 AM 9/10/2004

[Q45tech]

In thoery the 4.1/4.5=0.9111 [smaller engine] should get 9% better mpg but the 3.694/3.538=1.0441 [higher dif gear] reduces this to 9-4.4= 4.6% better on the highway at equal speed............1 mpg better at exactly the same speed. Around town I doubt there is that much difference. Maybe a few tenths of a mpg in city/traffic.

[duck3986]

My mileage has been averaging 20mpg which is what i've experienced for the last few years and I expect is pretty decent. I would guess I get around 24mpg on the highway.

Anyway, my intermittant "bogging/sluggish" behavior is driving me nuts. With 92k miles, I've ordered knock sensors and under plenum plumbing. Is there anything else I should do when I have the plenum off?

Anyone have pictures or suggestions of how to do a plenum on a '98Q?

If anyone lives in NH/MA and wants to do theirs at the same time, let me know.

Don

[maxnix]

In thoery the 4.1/4.5=0.9111 [smaller engine] should get 9% better mpg but the 3.694/3.538=1.0441 [higher dif gear] reduces this to 9-4.4= 4.6% better on the highway at equal speed............1 mpg better at exactly the same speed. Around town I doubt there is that much difference. Maybe a few tenths of a mpg in city/traffic.

My experience confirms this.