Hi all,
As some of you may know my 2.3 20v CQ has been suffering for a hot start issue, and the timing belt slapping at a specific RPM. Looking into the timing belt issue, I noticed that if I blip the throttle in neutral my revs fall far quicker than most videos I’ve seen of a 7A engines. When they hit baseline it’s like they would bounce off the bottom (bottom being idle rpm), rather than the ISV catching it in a controlled way. This made me wonder if the uncontrolled nature of my revs dropping would be the cause of the timing belt slapping as it’s sort of, catching itself from a free fall.
This lead me to wondering if the base idle had ever been set correctly. I recently removed the throttle body and set the TPS, idle switch and throttle stop screw precisely to the Bentley spec, and tested the TPS and idle switch (early 7A with Hitachi kit) and they passed every test. So with those set, ISV and MAF electrically tested and passed, I thought there’s no harm in setting the base idle to see if 1. The revs will drop in a more controller manner and 2, it’ll put me in a good position for looking further into my hot start issue.
With my Bentley manual in hand, I booked an MOT slot at a garage I’ve been having my MOTs done at for years who let me use their CO meter for the hour. So with crankcase breather hose clamped, dipstick pulled, temp to 80 degrees, fan off and A1 and B1 of the diagnostic port bridged I started measuring. One thing to note is that we couldn’t get the cap off the emissions test port, so we had no choice but to read from the exhaust. I don’t have a CAT ok the exhaust system, so keep that in mind when looking at the results.
The test equipment wasn’t the newer automated one that’s linked to VOSA. We tried that first but it kept timing us out. So we hooked it up to the older machine. This one used leads that hooked up to the battery to read RPM, although I’m not sure what I trust because from what I’ve read it needs to be setup depending on the engine?
The Bentley manual targets are 800rpm + 50 and CO range from 0.5% to 1%. It took a lot of tweaking of the bypass screw and the CO screw, but I got it to a point where the results were
RPM measured via battery - 950rpm
RPM on the tach - 800rpm
CO - 0.776 %
I didn’t take much notice of these other values at the time as my focus was on RPM and CO. I’m not sure if they can be trusted with measuring from the exhaust. Same could maybe be said for the CO level I guess.
PEF - 0.523
CO2 - 13.51%
Lambda - 1.044
O2 - 1.75%
HC - 302ppm
With the CO and idle looking to be at a good spot, I restored everything, blipped the throttle to exit test mode and the idle was rock steady, whereas before it would fluctuate rhythmically when warm. It used to idle high when warm, at about 1000rpm, rise to 1300r then drop. It did this with the idle switches properly set and ISV tested. If I blipped the throttle after the setup the revs did in fact drop in a controlled (not too slow) manner and settled and idle. You could see that maybe the ISV was catching the drop marginally late as it did bob below ever so slightly, but it all appeared to have been a step forward.
I drove it back to my unit and it felt fine. The jerk when releasing the throttle was a lot less harsh which is another reason I wanted to test this. Once I got back I turned it off and couldn’t start it again because of my hot start issue. So I left it overnight and now from cold with the new setup it just about started, revs are extremely low, then stalled almost immediately. I tried this several times, gave it some throttle and held it at around 1000rpm, then gradually released the throttle and it stalled again. Before doing the base idle setup it would start without issue every time. It used to idle at around 800rpm cold, but raise to about 1000rpm after some driving. After a while I decided to pull the plugs and they’re all wet with fuel and black. So obviously running way too rich.
I’m not sure what to do here at this point. Upon setting the base idle the RPM and CO appeared to be in a good spot and the way it was idling seemed like an improvement, but clearly something is up. The problem I also have is I can’t get it to the garage to run the test again because it won’t start at all. I don’t want to keep trying to start it, and I don’t have the original setup because the amount of tweaking made it impossible to keep track of. I don’t really want to blindly adjust from here either. I’ve checked for vac leaks too, as I wondered if I’d split the crankcase breather hose by clamping it but it appears intact.
Any thoughts on this would be appreciated. Feels like a constant up hill battle this car does! Constantly two steps back.
As some of you may know my 2.3 20v CQ has been suffering for a hot start issue, and the timing belt slapping at a specific RPM. Looking into the timing belt issue, I noticed that if I blip the throttle in neutral my revs fall far quicker than most videos I’ve seen of a 7A engines. When they hit baseline it’s like they would bounce off the bottom (bottom being idle rpm), rather than the ISV catching it in a controlled way. This made me wonder if the uncontrolled nature of my revs dropping would be the cause of the timing belt slapping as it’s sort of, catching itself from a free fall.
This lead me to wondering if the base idle had ever been set correctly. I recently removed the throttle body and set the TPS, idle switch and throttle stop screw precisely to the Bentley spec, and tested the TPS and idle switch (early 7A with Hitachi kit) and they passed every test. So with those set, ISV and MAF electrically tested and passed, I thought there’s no harm in setting the base idle to see if 1. The revs will drop in a more controller manner and 2, it’ll put me in a good position for looking further into my hot start issue.
With my Bentley manual in hand, I booked an MOT slot at a garage I’ve been having my MOTs done at for years who let me use their CO meter for the hour. So with crankcase breather hose clamped, dipstick pulled, temp to 80 degrees, fan off and A1 and B1 of the diagnostic port bridged I started measuring. One thing to note is that we couldn’t get the cap off the emissions test port, so we had no choice but to read from the exhaust. I don’t have a CAT ok the exhaust system, so keep that in mind when looking at the results.
The test equipment wasn’t the newer automated one that’s linked to VOSA. We tried that first but it kept timing us out. So we hooked it up to the older machine. This one used leads that hooked up to the battery to read RPM, although I’m not sure what I trust because from what I’ve read it needs to be setup depending on the engine?
The Bentley manual targets are 800rpm + 50 and CO range from 0.5% to 1%. It took a lot of tweaking of the bypass screw and the CO screw, but I got it to a point where the results were
RPM measured via battery - 950rpm
RPM on the tach - 800rpm
CO - 0.776 %
I didn’t take much notice of these other values at the time as my focus was on RPM and CO. I’m not sure if they can be trusted with measuring from the exhaust. Same could maybe be said for the CO level I guess.
PEF - 0.523
CO2 - 13.51%
Lambda - 1.044
O2 - 1.75%
HC - 302ppm
With the CO and idle looking to be at a good spot, I restored everything, blipped the throttle to exit test mode and the idle was rock steady, whereas before it would fluctuate rhythmically when warm. It used to idle high when warm, at about 1000rpm, rise to 1300r then drop. It did this with the idle switches properly set and ISV tested. If I blipped the throttle after the setup the revs did in fact drop in a controlled (not too slow) manner and settled and idle. You could see that maybe the ISV was catching the drop marginally late as it did bob below ever so slightly, but it all appeared to have been a step forward.
I drove it back to my unit and it felt fine. The jerk when releasing the throttle was a lot less harsh which is another reason I wanted to test this. Once I got back I turned it off and couldn’t start it again because of my hot start issue. So I left it overnight and now from cold with the new setup it just about started, revs are extremely low, then stalled almost immediately. I tried this several times, gave it some throttle and held it at around 1000rpm, then gradually released the throttle and it stalled again. Before doing the base idle setup it would start without issue every time. It used to idle at around 800rpm cold, but raise to about 1000rpm after some driving. After a while I decided to pull the plugs and they’re all wet with fuel and black. So obviously running way too rich.
I’m not sure what to do here at this point. Upon setting the base idle the RPM and CO appeared to be in a good spot and the way it was idling seemed like an improvement, but clearly something is up. The problem I also have is I can’t get it to the garage to run the test again because it won’t start at all. I don’t want to keep trying to start it, and I don’t have the original setup because the amount of tweaking made it impossible to keep track of. I don’t really want to blindly adjust from here either. I’ve checked for vac leaks too, as I wondered if I’d split the crankcase breather hose by clamping it but it appears intact.
Any thoughts on this would be appreciated. Feels like a constant up hill battle this car does! Constantly two steps back.
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