BeachKidd Posted February 8, 2014 Report Share Posted February 8, 2014 I have a 78' king cab w/ l20b but the bpt valve went bad and it's a hard part to find... What to do? Help! Quote Link to comment
KELMO Posted February 8, 2014 Report Share Posted February 8, 2014 If you like, I can get you a part # but there are quite a few choices so some information is needed. I am assuming the motor is an L20B Production date Federal of California emissions Quote Link to comment
datzenmike Posted February 8, 2014 Report Share Posted February 8, 2014 Well the easiest thing is to just leave it. The EGR will be disabled but unless there are inspections, it doesn't really matter. You don't even have to plug the hoses. Next is to get one from another L20B, they all had them. EGR 1/ Only on when motor up to full operating temperature and NOT idling. 2/ Off when motor cold, idling or at full throttle BPT varies the amount of exhaust gas recirculation in direct proportion to exhaust back pressure (engine load) subject to 1/ and 2/.. Quote Link to comment
ggzilla Posted February 8, 2014 Report Share Posted February 8, 2014 Bad BPT valve can result in a small exhaust leak or in a vacuum leak, depending on what's broken on it. Quote Link to comment
datzenmike Posted February 8, 2014 Report Share Posted February 8, 2014 It's ported vacuum from the carb and not intake vacuum. The port is above the throttle plate and is zero at idle. Vacuum is applied when throttle opened just like the vacuum advance on distributor. Quote Link to comment
BeachKidd Posted February 8, 2014 Author Report Share Posted February 8, 2014 Thank you mike Quote Link to comment
ggzilla Posted February 8, 2014 Report Share Posted February 8, 2014 Exactly. Will cause off-idle running problem if leaking on the vacuum side of the BPT. I had to fix a poor running one last year - plugged the hose and it ran better. Quote Link to comment
datzenmike Posted February 8, 2014 Report Share Posted February 8, 2014 I'm saying it's not an intake vacuum leak. The port is above the throttle plate. You could leave the hose off and would have no effect, same as the vacuum advance. Either hose off has no effect on the intake vacuum. If it ran better it was an ERG problem or the BPT was opening the EGR too soon or too much. Perhaps the EGR needed cleaning and has a small leak made worse by the BPT adding to it. Quote Link to comment
ggzilla Posted February 8, 2014 Report Share Posted February 8, 2014 It ran better after the vacuum leak was plugged. The EGR valve itself was not leaking nor stuck partially open due to needing a cleaning. What I found was that the BPT would not hold the vacuum. It isnt a huge issue like an idle vacuum leak. Quote Link to comment
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.