1990 Q with stumbling idle and weak at acceleration.

[mattd1979]

Hey, maybe you guys can help me narrow this problem down. I recently replaced my fuel assembly two the 2nd generation setup because I lost two injectors and I didn't have anymore backups. I had this setting around waiting to go in and figured it was a better time than any. I've done this conversion numerous times on other Qs without a problem until I work on my own. The problems I noticed after I replaced the rail was that the engine was now stumbling at idle and when I would accelerate, it acted as if the timing was off. It sounded as if it was under a heavy load. I later discovered that there was a vacuum leak in the fuel pressure regulator that came with the fuel rail. I also noticed that the fuel damper was allowing fuel to leak through the diaphragm and into the vacuum line. I replaced the fuel regulator and bypassed the fuel damper until I can get another. I found the power had increased some but still had the stumbling idle and the acceleration still wasn't at 100%. I'd say that it's around 70% now. I followed along in the FSM troubleshooting section which it stated to pinch off the pcv vacuum line and see if the rpm increases. It didn't, instead it went down. It then said to check the EGR valve. It said to press up on the diaphragm and it stated that it should stumble or stall. It didn't respond at all. In the past it would bog down when idling if you pulled up on the valve. I took the intake off again to replace the fuel pressure regulator and also I blew through the inlet of the EGR valve where the exhaust would connect and I moved the diaphragm up and down and found that it does work. It was blocking the flow as I blew through it, so I don't know what else could cause the engine not to respond to the change in the EGR valve. I figure whatever it is, it's what is causing the engine to stumble and be un-responsive to the operation of the EGR valve.

[Q451990]

Any chance of a massive vacuum leak, like a pinched pleum to runner seal? I'm assuming you removed some spacers or washers to make sure the phase 2 rails are jamed down into the runner ports with a good seal?

Heath

[mattd1979]

Yes, I made sure of that the second time I pulled the upper plenum to replace the regulator and bypass the fuel damper. I even sprayed a very flammable carb spray around the intake but there was no change. I notice that when I pinch the vacuum line that runs to the intake elbow ,or even the line that runs to the pcv valve, the rpms will drop slightly.

[mattd1979]

Tonight, I went ahead and sprayed around some more at the different areas of the intake but couldn't get a response from the engine. I ended up pulling one of the vacuum lines partially loose and sprayed and only then did it kick up in rpm. I disconnected the feed from the exhaust manifold to the EGR to see if it was plugged. I started it and you could certainly here the exhaust leak. So it isn't blocked at the pipe.

Matt

[black g50]

Not sure if we have same problem but,my Q stumbles going up over steep bridges even back firing from some where up front.Seen some posts about cleaning c.a.s. gonna have to check it out.

[mattd1979]

Here is another update...
I went ahead and pulled the EGR valve and checked the operation to verify and it is working. I started the car with the EGR hole on the intake side plugged and I then removed it expecting the car to stall and it kept on running without a problem. It was sucking air so it isn't blocked. I put my finger over it and noticed that it was a gradual suction, not rapid like the vacuum coming from the intake to the brake booster. I put my vacuum gauge on it and found that it was pulling almost 20 in hg vacuum. I disconnected the brake booster line and had to immediately plug the hole on the intake to brake booster vacuum port to keep the car from stalling. I then put the vacuum gauge on it and I got a reading of 21 in hg vacuum. This reading was taken while the EGR to intake hole was uncovered. I then covered the hole to see if the vacuum would climb but it didn't budge. After connecting the brake booster line back to the port, I took some carb spray and sprayed right into the EGR to intake hole and it didn't respond. The only time it would respond is if I used another vacuum source in which the RPMs would climb. According to the FSM diagram, it shows that the EGR to intake hole leads straight into the intake so I don't know why I'm getting no response from the deliberate vacuum leak I created at the EGR location but the car stalls when removing the brake booster line which is just as large of a port and is pulling harder. I also don't know if it is natural for the EGR port to have a gradual vacuum as compared to the other vacuum ports because I don't have another car to compare with. When I say gradual, I mean it climbs slowly up to almost the same vacuum as the other ports.

Matt

[mattd1979]

Just wanted to update and let everyone know that the stumbling issue was caused by an injector which turns out is from a 1997 or newer Q I think. All I know is when I got the rail, it had one red injector installed along with the rest as tan colored. I had two rails that I combined to make one and this injector passed as a good one. Apparently it flows less fuel and also has the fuel inlet located lower in the injector body. I replaced it with an injector that works but ohmed at 20 ohms. It made a world of difference. I now need to keep my eyes open for some more injectors to have for spare. The EGR issue was apparently a coincidence. The EGR system still isn't functioning correctly so that is going to be another thing to diagnose. I'm currently running the car with the fuel damper out of the loop because of the fuel leaking through the diaphragm and getting sucked into the intake through the vacuum line. It doesn't seem to be causing any problems not being there. Apparently that had been going on for a while and could be another reason my car was a bit sluggish due to the additional fuel being sucked in.

Matt

[Q451990]

Good to hear you're making progress. To answer your EGR question. The hole leading from the EGR valve into the intake is probably blocked or nearly blocked with carbon. It makes a 90 degree turn as it enters the main chamber of the plenum, and you'll find a lot of carbon at that bend. This is very common and needs to be cleaned from time to time.

Heath

[mattd1979]

Thanks for the heads up. That'll be on the agenda this weekend along with a new set of plugs and replacing that lawn mower fuel line that I'm using temporarily until I can get the right line for it. I don't think I'll be installing another fuel damper because it doesn't seem to be affecting how the car runs. Would I be better off buying my plugs from one of the online Infiniti shops or buy at one of the local auto parts stores?

[Q451990]

As long as you get the correct NGK part number, I think either option is fine on the spark plugs.

Heath

[mattd1979]

What do you think of the NGK Eridium compared to the double platinum plugs? I was reading on another forum about the Eridium only on the electrode and not on the ground like the double platinum plugs and that they were concerned with the ground tip wearing down and also concerned with the uridium tip getting so hot that it would come loose and fall into the engine. On another note they were stating how well the plug burned more of the fuel and increased power. What are your thoughts on this?

[mattd1979]

Just wanted to note a couple of things. First off, this car is more powerful now than it has been since I bought it back in 2006 when I worked at a local Nissan dealership. It keeps me down in the seat through all of the gears. I went ahead and bought the NGK Laser Iridium plugs after reading all of the positive reviews from different users. It uses Iridium for the positive electrode and Platinum for the ground electrode. Do you think it would be problem if I just leave the fuel pressure pulse damper out of the loop? Do you I would cause long term damage by not putting it in? The car is running great right now.

This weekend I'm going to go ahead and swap out the plugs which have about 70k on them I think and also clean all of the passages in the upper plenum for the EGR system and replace all of the tiny vacuum lines under there while it's off.

[Q451990]

I think I would replace the damper... It has to be there for a reason, right? If you can find a used one it's a good bet that it'll be OK. Yours is the first failure I've heard of.

Your call on the iridiums... I like to stay with stock parts, especially for ignition stuff. The electrode falling off concern is a big one. This used to happen on the Q with the Bosch +4 plugs.

Heath

[mattd1979]

Finished up about an hour ago from this post with replacing all small vacuum lines and fuel lines, cleaning inside the upper plenum and EGR port ( Which was about 95% blocked), and replacing plugs. The car no longer oscillates up and down during idle and it will now stall when pulling up on the EGR diaphragm . I'll let you know tomorrow how it drives. I've got to replace both coil pack harnesses because of the connectors shattering. I priced them new at around $150 a side. Unless you know where I can get replacement connectors that connect to the coil packs. Let me know if you do.

Thanks,
Matt

[mattd1979]

First drive since I did all of the above and it seems to be down on power off the line since clearing the EGR valve port. I'm figuring that the ECU is having to re-adjust to the change of additional air flow during cruise from the EGR now that it's cleared. Hopefully the power will return.

Matt

[black g50]

How does your exhaust look?Possible something is pluggn up.Changed out a plugged cat,power came back.Second one about do for replacing.

[mattd1979]

I went ahead and plugged the port that connects the exhaust to the EGR and took it for a drive and the power has returned. Much more responsive and less lag in throttle response. I don't have to give it as much throttle to go as I did before. I drove to Hilliard and back for a family get together and it seems to have done better on the gas mileage also. I also noticed that the pinging has stopped when I go full throttle in the upper RPMs. It was actually hotter that day then the days before at around 96 degrees.

Matt

[Q451990]

Sounds like your EGR was stuck partially open?

Heath

[mattd1979]

I wondered the same thing before I plugged it off. I noticed that the idle RPM picked up a little higher after I plugged the EGR off. I figured that if the EGR was stuck partially open that the RPM would have dropped when I plugged it off.

[Q451990]

I assume the EGR being partially open would lower the idle if opening it all the way woud choke the car down... it shouldn't behave like a normal vacuum leak since you're introducing non-combustbile exhaust gases instead of air.

Heath

[mattd1979]

I see what you mean. I suppose I'll be having to buy another valve since I already cleaned this one. It moves up and down good but I can't tell if it is completely closing. I suppose I could take some cleaner and spray in there to see if it will stay or seep through the valve.