Power loss

[Fouldsy67]

Good evening all I have a GQ RB30 carby rig driving it seems to lack power takes a long time to get any speed up and drops back to around 70 going up any hills
Starts and idles great has extractors 2 1/2 inch exhaust plugs seem fine all set to 0.9 mm fuel pumps good sits at 30 psi revs free at stop no missing compression is all around 165psi cold just stumped on what it could be any help would be helpfull
Cheers in advance

[mudnut]

Good evening all I have a GQ RB30 carby rig driving it seems to lack power takes a long time to get any speed up and drops back to around 70 going up any hills
Starts and idles great has extractors 2 1/2 inch exhaust plugs seem fine all set to 0.9 mm fuel pumps good sits at 30 psi revs free at stop no missing compression is all around 165psi cold just stumped on what it could be any help would be helpfull
Cheers in advance

Have a look at this thread. There is quite a bit of info about the carby in it. I found the second stage butterfly was sticking or not opening properly. http://www.nissanpatrol.com.au/forums/showthread.php?28517-RB30-Facts-Figures-and-Helpful-Hints

[mihit]

manual? auto? (clutch slip? TC issue?)

[Fouldsy67]

Manual and just found a box in the back with 3 carbys in it clutch is good no slipping there

[mudnut]

Manual and just found a box in the back with 3 carbys in it clutch is good no slipping there

The carbies playing up is a common thing for these old buses. I've been on the lookout for a spare carby so I can put a kit in it and keep it for long trips in remote areas.

[Big Girl]

Same problem, diesel 3L GU 2004. It seems to know when it's close to home and does it on the same hill every time! On the third MAF sensor. New air filter and thorough clean of the intake. She will be coasting along fine then suddenly loses a little power, like she is suddenly driving into the wind. And she does it constantly when towing the caravan! Any ideas welcome. No we haven't done a diagnostic, that's next.

[mudski]

Same problem, diesel 3L GU 2004. It seems to know when it's close to home and does it on the same hill every time! On the third MAF sensor. New air filter and thorough clean of the intake. She will be coasting along fine then suddenly loses a little power, like she is suddenly driving into the wind. And she does it constantly when towing the caravan! Any ideas welcome. No we haven't done a diagnostic, that's next.

Possibly a boost leak. Are you running the original intercooler?

[Big Girl]

Possibly a boost leak. Are you running the original intercooler?

Yes. Had the head replaced last year. Will contact the shop and book her in for diagnostics. What are your thoughts?

[mudski]

Yes. Had the head replaced last year. Will contact the shop and book her in for diagnostics. What are your thoughts?

Well if you are running the original intercooler, I would say its leaking. Check the underside of the cooler. Is is clean? Or does it have oil deposits on it.

[Big Girl]

Well if you are running the original intercooler, I would say its leaking. Check the underside of the cooler. Is is clean? Or does it have oil deposits on it.

Thanks heaps Mudski, much appreciated. I did some research and will get under the bonnet this afternoon. Regards, Louise

[mudski]

Thanks heaps Mudski, much appreciated. I did some research and will get under the bonnet this afternoon. Regards, Louise

No probs. The original intercoolers are well known to leak. If it is, you will be leaking precious boost out hence giving you poor performance under load. Let us know how you go.

[BillsGU]

Simple test. Remove the IC and tape up the inlet and outlet ports. Submerge it in a basin full of water and if it has a leak you will see the bubbles. WHEN (not IF) you see the bubbles - replace it with an after market IC. As I said - simple.

[mudnut]

Manual and just found a box in the back with 3 carbys in it clutch is good no slipping there

Private Message sent, regarding the carbies.

[mihit]

Simple test. Remove the IC and tape up the inlet and outlet ports. Submerge it in a basin full of water and if it has a leak you will see the bubbles. WHEN (not IF) you see the bubbles - replace it with an after market IC. As I said - simple.

Maybe silly question (I don't deal with anything younger than the age of consent... or with "little" engines...)

But can the thing not be braze/weld repaired??

[BillsGU]

But can the thing not be braze/weld repaired??

The original IC has crimped on ends. The crimps seem to be difficult to seal. It can be repaired - and a more efficient core installed - and welded on. Getting someone to do it is sometimes an issue. Often easier (and sometimes cheaper) to go aftermarket.

[Big Girl]

No probs. The original intercoolers are well known to leak. If it is, you will be leaking precious boost out hence giving you poor performance under load. Let us know how you go.

Finally got it onto a dyno - the boost solenoid is sticking. I shall do some homework before I replace it, just in case I need more than just the solenoid unit. Thanks for the lead, much appreciated.

PS. The air hose to the rear of the intercooler had not been tightened when the head was replaced a year ago. After tightening, the problem was not as bad, but still there. I booked it in for the dyno diagnostic this morning. Hopefully this will sort it.

[Big Girl]

Update:
Diagnosis, no codes, no idea.
Confirmed she has a new fuel filter, air filter, MAF sensor, cleaned MAP sensor, new boost solenoid, new airlines, and we have cleaned the hoses thoroughly. Done everything conceivable in the boost lines.
Another point: My other half recently found a Nissan Patrol for sale, with a boost problem. He made contact to ask about the boost problem - they don't know whats wrong, that's why it's being sold.
AND my mechanic who did the testing had another one in only two weeks ago and they didn't resolve that problem either.

I shall contact the local Nissan dealership and talk to one of their mechanics to see what I can learn. Next step will be collecting information on a thread for others to add to until we find the solution.

[Big Girl]

Well, Big Girl still has a boost problem.

She has the new MAF sensor (plus new air-filter and thorough clean out before it went in)
New air-pressure hoses (the lot)
A new Boost solenoid (apparently the new version is an upgrade from Nissan) - as recommended by the mechanic who checked for codes
I removed the shim (trying anything now!)
Installed a new fuel filter


The mechanics recommendation: no idea - take it to Nissan...

and now I'm ready to take her to a 'professional' dyno mechanic.
I asked around, the word is: DON'T take it to the local Nissan workshop.

[Bidja]

Well, Big Girl still has a boost problem.

She has the new MAF sensor (plus new air-filter and thorough clean out before it went in)
New air-pressure hoses (the lot)
A new Boost solenoid (apparently the new version is an upgrade from Nissan) - as recommended by the mechanic who checked for codes
I removed the shim (trying anything now!)
Installed a new fuel filter


The mechanics recommendation: no idea - take it to Nissan...

and now I'm ready to take her to a 'professional' dyno mechanic.
I asked around, the word is: DON'T take it to the local Nissan workshop.

Should have started your own thread but we are here now.

So you have fitted a new vacuum solenoid, pull the hose off the solenoid end port (blue hose in my first picture) and connect in directly to the VNT Vacuum actuator, where the red hose is shown on the second picture:

with eng at idle _ does the rod rise up with the lever hard against the vane limit stop screw?

Still with engine at idle, pull the same hose off the VNT Vacuum actuator _ does the rod drop down to bottom of stroke (approx 10mm)?


PS: before doing the above direct connection / vacuum test to the VNT Vacuum Actuator, u can check the rod/lever position with with vacuum solenoid connected as it is currently set up:

eng at idle have the hose connected to the actuator "ON" and then pull the hose "OFF" and you should see the actuator rod rise and drop respectively. Y/N?

Do this and we will then go from here.