91 Q45 sluggish performance

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ptcorbman
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Joined: Thu May 17, 2018 1:58 am
Car: 1991 Q 45

91 Q45 sluggish performance

Postby ptcorbman » Mon Aug 06, 2018 1:19 pm

Hi all
This car can barely get up to speed from 0-30 then runs well , once on the highway seems to be able to go as fast as I want , I am looking for where to start checking to improve low end performance ?


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goody90q45
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Car: 1992 Q45 (sold)
Location: Orangevale, CA

Re: 91 Q45 sluggish performance

Postby goody90q45 » Wed Aug 08, 2018 8:21 am

Ohm test your knock sensors and fuel injectors. Chances are pretty good that after 25 years one or both of the KS are dead and don't be suprised to find a dead or dying FI or 2 also.

http://q45.org/ohminjectors.html

ZiprHead
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Car: 1999 Q45 base
Location: Saginaw, MI, USA

Re: 91 Q45 sluggish performance

Postby ZiprHead » Sat Aug 11, 2018 7:59 am

goody90q45 wrote:
Wed Aug 08, 2018 8:21 am
Ohm test your knock sensors and fuel injectors. Chances are pretty good that after 25 years one or both of the KS are dead and don't be suprised to find a dead or dying FI or 2 also.

http://q45.org/ohminjectors.html
Agree completely with this.

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HG50
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Re: 91 Q45 sluggish performance

Postby HG50 » Sat Sep 01, 2018 9:33 pm

So did you fix the problem? Usually it’s repaired with the suggestions posted above.

sandydennis11
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Car: 1996 Q45 160,000 miles purchased new in 1995
Location: san francisco ca

Re: 91 Q45 sluggish performance

Postby sandydennis11 » Sun Sep 02, 2018 10:21 am

Well this '96. Q is acting up again, similar to your '91.

Probably the knock sensors or ignition coil.Cylinder coils 3 and 5 were replaced 3000 miles ago with same symptoms . I suggested to change all of them though only the service guy said towait.
So will find out Tuesday if another 2 grand goes into her. Oh Well
.

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Q451990
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Re: 91 Q45 sluggish performance

Postby Q451990 » Sun Sep 02, 2018 2:52 pm

Coil failures are pretty rare on this series of Q45. Fuel injector failures are pretty common.... it's also possible to have a fouled spark plug on the corresponding cylinder with the failed fuel injector.

Drake57
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Car: 1992 Q45, 1990 Q45 (parts), 06 Sportster XLC, 85 XJ6, 08 4Runner, 89 Suburban 4WD, 75 Honda CT90
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Re: 91 Q45 sluggish performance

Postby Drake57 » Mon Sep 17, 2018 8:28 am

goody90q45 wrote:
Wed Aug 08, 2018 8:21 am
Ohm test your knock sensors and fuel injectors.
My 1992 has similar problem, though not so pronounced: It is just cold shouldered, often times backfires though intake when throttle is opened abruptly, as in accelerating from stop, or will stutter and stumble until throttle is let off and reopened, and engine RPM increases, then sometimes bucks when opening throttle at 45mph when in high gear after coasting. It really just seems lean.

I've never tested or replaced KS's. FI's are Deatschwerks retro fits, I've replaced all hoses under plenum, fuel pressure regulator, coils 2,4,6,8, tested for vacuum leaks, swapped MAF, and throttle position sensor, to no avail. Will KS's cause lean AFR?

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goody90q45
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Car: 1992 Q45 (sold)
Location: Orangevale, CA

Re: 91 Q45 sluggish performance

Postby goody90q45 » Mon Sep 17, 2018 9:02 am

Go ahead and ohm test the FI and KS to verify all is good. A couple of other things to check...

Sounds like the engine may be fuel starved. Could be the FPCU going bad. Try bypassing the FPCU with a jumper from the connector pin shown in the pic to ground. FPCU is under the rear deck and you can get to the connector through the trunk. The FPCU will run in high speed only while bypassed and if the acceleration problem goes away you've found the issue.

Image

The MAF and TPS connectors are not waterproof and can corrode. Tighten the female pins, clean off any corrosion and coat with dielectric grease. Can't hurt, should help.

Image

Drake57
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Car: 1992 Q45, 1990 Q45 (parts), 06 Sportster XLC, 85 XJ6, 08 4Runner, 89 Suburban 4WD, 75 Honda CT90
Location: Georgetown, TX

Re: 91 Q45 sluggish performance

Postby Drake57 » Mon Sep 24, 2018 8:50 am

KS's ohm tested at 600K, and 10M, so looks like at least one is fouled. Wow, if this is the reason mine sometimes runs like hammered sh*t, that's an economical fix, except for the pain of the plenum.

ptcorbman
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Car: 1991 Q 45

Re: 91 Q45 sluggish performance

Postby ptcorbman » Thu Oct 04, 2018 11:41 am

Update : KS ohm test failed ,injectors OK . I finally got brave enough to tackle replacing the KS's , it has been an ordeal , previous owner had run over a traffic cone damaging the radiator and fan , overheating the car .
When removing the intake manifold most hoses crumbled and knock sensors were melted into a puddle .
As a former pipe-fitter and plumber I was able to re-plumb the many vacuum lines after installing new knock sensors . I added an electric fan for the radiator , car finally ran like the engine should . Test drive resulted in steam from under the intake , appears to be the hose immediately behind the thermostat housing .
Stuck thermostat now ?

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Q451990
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Re: 91 Q45 sluggish performance

Postby Q451990 » Fri Oct 05, 2018 7:21 am

Wow... That sounds like one heck of an overheat!

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Re: 91 Q45 sluggish performance

Postby J30tChumpCar » Mon Oct 15, 2018 9:21 pm

First one I bought had a bad rad and 2 injectors, knock sensors were a melted mass, plastic label on oil filter shriveled from the heat, ran strong after repairs but had a piston knock in the morning. That engine was shelved in fear it would give up, car got/still gets picked for parts...

Stuck thermostat wont make steam there, did you find the water leak?


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