Aceleration problem

[Fridge]

Been a while since I posted. I have a 91 q45 that I built for my son. He is away out of state so I have been driving it. Man Ilove this car he may not get it back lol.

I put a jdm engine in it and put in the new chain guides what fun! It ran great for a while but now has a problem over 3500 rpm. If you baby it she runs great but if the rpm gets high the engine starts sputtering and will sit at 4500. It is not related to throttle position as it will do it at part throttle but really acts up if you floor it. Also the idle is rough. I am going to clean the maf again today and see if anything changes.

I have a few more problems I need to clear up so bear with me for a while.ThanksFrige

[maxnix]

Best to post your mechanical problems in the Infiniti Online Mechanic Forum for a quicker in depth response.

By the way, how's the fuel pump? Fuel filter?

[elwesso]

Moved to the online mechanic.

Its probably MAF of CAS related problem, do you have any codes???

Check this thread out...

zerothread?id=134486

Sounds similar to these symptoms.

[gniknave]

I'd wiggle the CAS connector with the car running. If the car stalls when you do this, then that might be your problem. I had a similar incident a while back and it ended up being a cracked wire leading to the CAS connector. When I had this issue, sometimes I'd get a MIL and sometimes not.

[Fridge]

I was out of town for a bit so the q repair was put on hold. OK I cleaned the connector to the maf (it was green) and put blub grease on it. No change. I shook the connector to the cas and it seems ok it will start stalling only after it gets almost removed. There are no codes stored as far as I can tell the check engine light is not lit. So where do I go from here? I will change the fuel filter today although it is fairly new.Reid

[Fridge]

Oh,Also it idles rough.

[Fridge]

After reviewing other posts I ohmed the injectors. They all ohmed at 29-31 through the harness. I pulled a couple of the connectors at the front #1 & #2 And they are green with corrosion. Although both ohmed out ok. How do I clean these or do I need to replace the connectors? I will go ahead and remove all the injectors and replace the o rings I am sure they need it. Now that should be fun since they seem to be stuck in the holes any tips on removal without destoying them?Thanks for the helpReid

[Jesda]

-All- ohmed at 29-31? Did you make sure to remove the key, close the door, and make certain that all lights were off when you measured them?

[Q45tech]

How do you know you VOM is accurate? Low VOM internal battery will give wrong readings....they must measure 12 ohms +- 1ohm thru harness.

[goody90q45]

Your readings could be correct but something sounds fishy. Follow Tech's advice and get a 10 ohm resistor from Radio Shack (about $1) to verify your voltmeter accuracy. Your meter should read very close to 10.0. There's lots of posts out there on the steps for removing injectors but starting with PB Blaster (or equivalent) is probably a must.

[Q45tech]

Be careful to read the resistance tolerance of resistors you buy..........some of the reject bulks repackaged for RS can be +-10%.

http://www.online-calculators....s.php

Look for 4th band = gold +- 5%

12 ohms is a common value in the 5% group

[sijoko]

To me, it sounds like the fuel pump and the fuel pump controller. How many miles on the pump?

It could also be the fuel filter but you said that you changed it recently.

[DrewQ45]

Sounds like CAS to me. Symptoms sound very similar... Take a read here...

zerothread?id=144460

[DrewQ45]

CAS on ebay... pretty good price... check compatability

http://cgi.ebay.com/ebaymotors...QrdZ1

[Q45tech]

CAS almost never go bad internally [high mileage ones can have rust dust that can cause flakey timing drop outs [6,000 rpm misses] at extremme rpms.

Usually dirty corroded connectors is the only problem.

[Fridge]

Its been a while. First the good news I got my injectors changed. I really think they needed it the plastic had broken off of some of them and went somewhere.. The bad news it runs terrible almost the same no power above 3k and it has a dead miss. I took it to a muffler shop to check the cats and they were working. 100 degree temp diff past the cats. I already changed the fuel filter it was clean. So maybe the maf? how do I check it? ThanksReid

[96Qowner]

It looks like you and Dustkicker are having the same problem:

"At idle, and up to about 35 mph, I can rev up to 4500 rpm or more. But once I reach 40 mph, it won't exceed 3400 rpm! If I am going, say 60 mph, and punch the gas, it just sputters and creeps along. Same if I am going 70...takes forever to reach 80 mph. I can't risk trying to pass at any speed unless there is lots of time/room."

zerothread/177983

There's no good way to test the MAF, other than a Consult reading. And bad MAFs usually cause severe bucking and missing, rather than simply killing acceleration. If you could borrow a known good one, you could swap it. Anyone else here from Houston?

Check your CAS connector?

You can also bypass the FPCU to give the pump full power, with a jumper.

"Dennis' suggestion to ALWAYS keep an aligator-clip wire in your trunk comes into play while your're stuck on the roadside shoulder.

From the Q45 trunk compartment, simply:a) Remove the forward-facing bulkhead, AND ...b) disconnect the fuel pump control unit connector ... ANDc) Jump the ground wire (see photo).

This totally bypasses the fuel pump control unit, which will handily get you home (albeit with a fuel pump whirring away at top speed)."

zerothread?id=73822
Modified by 96Qowner at 2:58 PM 6/1/2006

[Q451990]

Don't discount the possibility that if your injectors were bad, your plugs could be fouled to the extent that they won't fire correctly. On both of my injector deaths, the plugs were carbon fouled so bad that I had to remove and clean them to get rid of the miss.

I agree with others here though, that it could very well be fuel pressure related.

Heath

[Dustkicker]

96QOwner is right...this sounds exactly like my 92Q's problem I have been dealing with the past month after running out of gas. Mine has been trouble shot down to "a bad fuel pump" issue.

I have ordered a new FP, should get it from Joe by Tue/Wed and will install it then. Fridge, I will let you know if it resolves my problem.

Frank

[Fridge]

I am looking for a pressure gauge and I will check that next. I am sure the miss is a fouled plug I hope the plastic from the injector did not get stuck in the valve

[maxnix]

96QOwner is right...this sounds exactly like my 92Q's problem I have been dealing with the past month after running out of gas. Mine has been trouble shot down to "a bad fuel pump" issue.

Frank

That means that any detritus that was floating around in the tank is now in the fuel lines.

Be sure to inspect your tank when you do the fuel pump, and if you see anything, even a slight coating of grime, take out your fuel tank and have it steamed cleaned. Blowout your fuel lines and replace any rubber for longer life. Replace filter, and if you still have problems or it hasn't ever been done, fuel rail flush.

[Fridge]

Well I found a fuel pressure gauge. The pressure reads 35 to 40 psi and stay fairly steady when you rev the engine. Is this good? My son really wants his car back I will pull the plugs and check them next.Reid

[Q45tech]

The fuel pressure regulator controls fuel pressure [asumming the pump is running at the correct rpm for the load range [why FPCU has 3 speeds as controlled by ecu based on TPS voltage [LOAD].

The plenum vacuum [1"HG > 22" HG] creastes the CONVERSE in fuel pressure WOT = 1" = 44 psi........................IDLE/CRUISE =18-22" = 34psi

Anywhere between fully open and closed or almost closed throttle the fuel pressure will be between these two extremes based in plenum pressure.

A good test is to squeeze shut the return line [smooth pliers] as it comes off engine which should cause psi to rise from 34 to >60psi.......tests pumps capacity [but not perfect because the volume at idle is do low].

Consider that at idle the 2 msec injection is 2/11=18% and the 34/44 sqrt =12% and the rpms are 1/10 so all together the flow is about 1/50 of the flow at max rpm WOT.

The first thing we check with bucking at high rpm is the fuel pump and we tape a psi gauge to window and drive to max rpm in 1st and 2nd to make sure psi stays at 44 psi as the rpms rise.

[maxnix]

Also, if you get totally stumped, texasoil has posted a shop he uses in Houston.