91LS400vgb

Hello everyone, I have 2 1991 LS400's and one of them is throwing a 71 egr code. I diagnosed the entire system as per the FSM, and even exchanged some parts between the 2 cars to confirm that certain parts were good. All the major parts check out, including the EGR valve, modulator valve, VSV and vacuum port switch. There is one difference between the 2 cars and that is the vaccum readings from the E-Port on the throttle body. On the good car, I get vacuum readings of 5 (in. Hg) and 12 in. Hg at 1500 RPM and 2000 RPM, respectively. However, on the car throwing the code, I only get 2.5 in HG and 6.5 in HG, which is much lower than the good car. I think this vacuum may be too weak to be effective by the time it reaches the modulator and egr valve. I checked the "P" port on the TB, and both cars are 22.5 in Hg at idle. I sprayed some air intake cleaner, (which I can see made it into tthe TB) and compressed air into the E-port and tried running some wire down into it. I wasn't really able to get any wire to go all the way through as I couldn't find something thin and flexible enough. Aside from the e-port being partially clogged, does anyone have any ideas what could be happening here? Thanks.

91LS400vgb

I think I'm going to remove the throttle body to do a complete cleaning. I'll post an update if and when I solve my 71 error code issue. Could someone post their vacuum readings from the TB "E port" at 1500 and 2000 RPM?

python

iTrader: (4)

good luck..i posted on this very code last week or so and not one person on here replied..if a guy gets new rims or does something cosmetic then this place erupts..need some help? u will be hard pressed to find much of anyone who will help u out(excluding KANSAS) or maybe the knowledge isnt there..u also get a lot of people posting with problems then they never post the results.
anyways,check for vacuum leaks from any and all lines including the ones on the throttle body itself..did u check vacuum with the car driving down the street? if not u need to. u applied vacuum to the egr and the engine died or stumbled? clean the filter in the solenoid..clean the egr and the passages for it..these are some of the things u need to do..hope this helps you out

91LS400vgb

thanks python, yes i did all those things. I applied some vacuum to the egr and it stumbled. I also tested the vsv by putting 2 vacuum gauges on it - one on the input side and one to the output side. I applied 5 in. Hg to the input side and read 5 in. Hg on the output side. I then applied 12v to the electrical leads and it released the vacuum on the output side as it should. In fact, I went further and swapped the modulator valve assembly and vsv from my good-running LS400 with the ones from the code-throwing LS400 and all the parts check out fine. I also connected a vacuum gauge in series at various points in the system and drove around with the gauge in the car, observing the readings. It looks like I'm basically not getting enough vacuum from the TB e-port. i found some good sources on testing the EGR system out - these two articles have a lot of useful info about our EGR system:

http://www.motor.com/magazine/pdfs/082009_04.pdf
http://www.motor.com/magazine/pdfs/092009_04.pdf

I have an advantage in that I have 2 LS400s - one with a functioning EGR system and one with the 71 code. The difference is in the vacuum reading I get from the E port of the Throttle Body. The vacuum gauge on the good car responds more quickly and shows nearly double the vacuum from the E port at 1500 & 1200 RPM as the car with the code. At this point my thinking is that the E port is either partially clogged or I am losing vacuum somehow, perhaps around the TB tubing - I am going to spray some water on it to see if it gets suctioned in. Like I said, I'll post an update if I solve this.

python

iTrader: (4)

yes please do as im curious to know what ur problem is..thank you!

91LS400vgb

Well, I removed the throttle body and did a complete cleaning with air intake cleaner and a toothbrush and rags. I cleaned it very well. I didn't realize how small the e-port hole was on the inside of the TB. I couldn't even see it until I wiped off the surface. I stuck a paper clip into it to make sure I cleared it out well. Unfortunately, no one had a TB gasket in stock, so I have to wait a few days to get one before I can reinstall. Like I said, the e-port wasn't completely clogged so I am somewhat skeptical that this is going to make any difference.
While I had the throttle body off, I also checked it as per the FSM and discovered that the TPS needed adjustment. The FSM says that there should be continuity between E2 and IDL on the electrical connector while a 0.40 mm thickness gauge is inserted between the throttle screw and lever. I loosened the two screws and adjusted the TPS as per the FSM and also confirmed that there was no continuity while using a 0.85 mm gauge as per the FSM. I don't think the TPS has any connection with my vacuum reading.
I'll post an update once I install the TB.

3UZFTE

Not sure if the readings are normal or not, but I know that some vacuum ports on the TB are a ported vacuum, and are designed to flow low vacuum until a higher RPMs are reached, than it pulls a larger vacuum as the throttle plate opens up past that hole.

91LS400vgb

yepper, the E port is ported, as is the R port. The P port is on the inside of the butterfly at idle, so it always gets vacuum. My E port, for example, does get incrementally more vacuum as the throttle is opened, but I just haven't been able to find a reference somewhere for what that vacuum should be at, say, 1500 and 2000 rpm. I can only assume it is too low based on the readings I get from my other vehicle, but I wonder if others see comparable vacuum.

python

iTrader: (4)

keep us posted,and thanks for the info

jerryparks

iTrader: (1)

I would recommend that you make sure that the long rectangular box under the TB is securely
tight with the TB. I had vac problems and discovered that the box was not secure and leaking air. I then removed the TB and installed some gasket material on the top of the box around the
connection. This fixed my problem and the stumbling stopped. Hope this is of some help.
BTW: after cleaning the TB, a had a good improvement in performance. I also installed a new set of plugs, which I think also helped.

91LS400vgb

thanks - will keep that in mind

3UZFTE

I think it's safe to say your getting vacuum to the valves, I would believe there is something else failing causing the problem as opposed to clogged vacuum lines, hoses, etc.

91LS400vgb

Well, not really. I ran through many different tests - one was to place a Tee inline before the "P" vac modulator port so I could insert a vacuum gauge there and drive around while watching the gauge - I did this on both vehicles so I could see what I should expect from the good car. The bad car displayed no vacuum at all. That's what led me to check vacuum at the TB "E" port and that's where I saw the big difference between the 2 cars. The good car is showing twice as much vacuum at the "E" port than the bad car at the same RPM. I'm still waiting for the gasket to arrive so I can reinstall the TB and see if cleaning made any difference.

It would be helpful if someone can share their vacuum readings from the E port at 1500 and 2000 RPM. What I do is lay the gauge by the windshield so I can see the gauge and the tach reading from inside the car at the same time.

91LS400vgb

I finally solved the problem. Not surprisingly, the throttle body cleaning had no effect. (It wasn't a complete waste since I now have a sparkling clean TB.) The problem was the hard steel vacuum line that travels from the TB e-port and branches to the Vacuum Modulator and BVSV. The line was 90% restricted. I bypassed it by using a rubber vacuum hose and ty-wrapping it to the steel lines. The EGR now functions perfectly!

j2b4o

Good job!!
Thanks for telling us the conclusion! I'm sure it will help someone some day.