Ryan S Posted October 18 Report Share Posted October 18 Hello, I know there are many forums related to starquest’s stumbling/bucking past ~3500rpms but none seem to help me out. I recently got my car to run and drive fantastic although I can’t get into boost without it stumbling/sounding like rolling anti-lag. In neutral it’ll rev perfectly without any hesitation, I’ve done a couple pulls while watching my wideband and it tanks to 10afr but I know it’s going lower. So, does anyone know why it’s going pig rich when doing a pull? And it seems to only do it when I get to around 3500rpms. I’ve tried multiple different things, I’ve replaced multiple things but maybe I’m missing something that can cause my issue? I have 40psi while idling, but unfortunately don’t know what it’s doing under boost. I’ll try to rig up a camera to watch it while accelerating. Any help would definitely be appreciated! Thanks! Link to comment Share on other sites More sharing options...
psu_Crash Posted October 19 Report Share Posted October 19 That sounds a lot like the vacuum advance on the distributor has gone bad. If you stay out of boost while driving will it still rev slowly? You can do a quick test to see if it holds vacuum. Stick a line on the vac advance and suck on it. Hold the vacuum with your tongue. Or if you have a mity vac, I suppose that would work too. If it bleeds off quickly that's definitely a problem. Link to comment Share on other sites More sharing options...
Ryan S Posted October 19 Author Report Share Posted October 19 13 hours ago, psu_Crash said: That sounds a lot like the vacuum advance on the distributor has gone bad. If you stay out of boost while driving will it still rev slowly? You can do a quick test to see if it holds vacuum. Stick a line on the vac advance and suck on it. Hold the vacuum with your tongue. Or if you have a mity vac, I suppose that would work too. If it bleeds off quickly that's definitely a problem. Yes if I drive like a grandpa it does great. Lol. as for the vacuum advance, it does indeed bleed off. It bleeds slowly but i suppose that would still be a problem. I swear I tested that a while ago, and it held vacuum perfectly. Guess she finally went bad. do you know where I could get one by chance? thanks for your reply! Link to comment Share on other sites More sharing options...
psu_Crash Posted October 22 Report Share Posted October 22 That will happen. Well Mikie used to have them. Looks like he's out of stock now though https://mksmotorsport.com/product/vacuum-advance-oem-g54b/ I'll take a look around the shop. I may have one. If I find it and it tests good I'd send it for the price of shipping. That may not be THE problem, but you can at least move on from there. 1 Link to comment Share on other sites More sharing options...
Ryan S Posted October 22 Author Report Share Posted October 22 25 minutes ago, psu_Crash said: That will happen. Well Mikie used to have them. Looks like he's out of stock now though https://mksmotorsport.com/product/vacuum-advance-oem-g54b/ I'll take a look around the shop. I may have one. If I find it and it tests good I'd send it for the price of shipping. That may not be THE problem, but you can at least move on from there. Ok sounds good, let me know! and yeah I don’t know what my problem is lol. I’ve tried a different MAF, MAP/boost solenoid, IAT sensor. I don’t know what else could cause rich conditions under hard acceleration. also these fpr’s are vacuum referenced right? Like it adds fuel pressure as the vacuum goes up? If so do you think I could cap off the regulator and see what happens? Cause if it’s getting wayyy too much fuel under load I wonder if the regulator isn’t regulating it correctly. It’s an adj. one from Mikie. I also thought about a boost leak, but the car runs and drives great. It’s just when I wanna get on it, it bucks. But if I creep up on boost it’ll see 7psi perfectly in 4th. The other gears it don’t make 7psi, but I know those gauges are not very trustworthy. any other thoughts? Let me know! thanks! Link to comment Share on other sites More sharing options...
psu_Crash Posted October 22 Report Share Posted October 22 (edited) I didn't make it out to the shop last night. I'll try to remember to take a look tonight. Yes, the FPR is boost referenced. I wouldn't cap off the FPR though. That could cause it to lean out bad and be a worse problem. Inatalling a mechanical fuel pressure gauge is the best way to tell if the pressure is increasing as it should. Run it temporarily and tape it to the hood for a quick check. The coolant temp sensor could be making it run rich too, thinking it is in warm up all the time. How do AFRs look when you slowly roll into it? Have you verified the timing? Boost leak shouldn't cause those issues, but I've seen stranger things. Still on coffee #1 for the day, so I'll think about it. I'm sure it's something simple, finding it is the fun part Edited October 22 by psu_Crash Link to comment Share on other sites More sharing options...
kev Posted October 22 Report Share Posted October 22 It's most likely a vacuum advance. Can test it with a vacuum pump to see if it holds but I've seen these sometimes hold vacuum but not boost. The diaphragms rot away with time. Unfortunately, the suppliers who use to carry aftermarket vacuum advances have seems to stopped. Mikie has been trying to work with them to get batches made but this has been an issue for a few years now. The only current solution is to buy the full distributer....so what was once a $15 purchase for a typical starquest 'tune-up' is now $250! it sucks but one of the things we face with these already rare cars approaching 40 years of age. Link to comment Share on other sites More sharing options...
Ryan S Posted October 23 Author Report Share Posted October 23 On 10/22/2025 at 6:24 AM, psu_Crash said: I didn't make it out to the shop last night. I'll try to remember to take a look tonight. Yes, the FPR is boost referenced. I wouldn't cap off the FPR though. That could cause it to lean out bad and be a worse problem. Inatalling a mechanical fuel pressure gauge is the best way to tell if the pressure is increasing as it should. Run it temporarily and tape it to the hood for a quick check. The coolant temp sensor could be making it run rich too, thinking it is in warm up all the time. How do AFRs look when you slowly roll into it? Have you verified the timing? Boost leak shouldn't cause those issues, but I've seen stranger things. Still on coffee #1 for the day, so I'll think about it. I'm sure it's something simple, finding it is the fun part Sounds good, take your time! I have a mechanical gauge already, just don’t have a way to see what it’s doing under load. I’ll try to tape my phone in there when I get the chance to fiddle with it again. as for the coolant temp sensor, it is also new. But I’ve heard that these aftermarket ones aren’t the best for these cars. Isn’t there a way to put a 200ohm resister in there to tell the ECU it’s “fully” warmed up? second that, I’m pretty sure it works fine. At cold start it’s around 11-12 afr but once it warms up it idles around 14.5 afr. So that should actually work. If I remember correctly even when you slowly roll into it, it still goes pig rich. It’s just slower lol. Like when I roll into it, it’ll be around 13 afr but when I slowly get into it more it tanks to 10 afr i have not verified the timing. I’ve been wanting to do that but just don’t have the time, nor the real knowledge how to do it. I have the FSM so hopefully it’ll help me out. thanks for your response! Link to comment Share on other sites More sharing options...
Ryan S Posted October 23 Author Report Share Posted October 23 On 10/22/2025 at 8:05 AM, kev said: It's most likely a vacuum advance. Can test it with a vacuum pump to see if it holds but I've seen these sometimes hold vacuum but not boost. The diaphragms rot away with time. Unfortunately, the suppliers who use to carry aftermarket vacuum advances have seems to stopped. Mikie has been trying to work with them to get batches made but this has been an issue for a few years now. The only current solution is to buy the full distributer....so what was once a $15 purchase for a typical starquest 'tune-up' is now $250! it sucks but one of the things we face with these already rare cars approaching 40 years of age. Yeah, my vacuum adv. does bleed off when you apply vacuum. it does look to be factory, so I bet she’s ready to retire. You gotta pay to play, which isn’t a big deal to me. I know parts for these cars are becoming nonexistent so I’ll do whatever to keep mine on the road. thanks! Link to comment Share on other sites More sharing options...
psu_Crash Posted October 24 Report Share Posted October 24 (edited) Found it and it tests good under vacuum and pressure. Should clean up well. The rust on the bottom side isn't bad. I'll send the whole distributor. I don't have a use for it since going MPI and ditching this unit. Shoot me a PM with your shipping address. Edited October 24 by psu_Crash 2 Link to comment Share on other sites More sharing options...
Ryan S Posted November 13 Author Report Share Posted November 13 Update - So after getting psu’s vacuum advance, the car runs absolutely fantastic. It pulls hard all the way to 6k rpm’s! I do have some new problems though… I was coming to a stop and all of sudden my fuel pump was wining pretty bad, then came the side effects. It barely idles now, but still does great under load so I’m not sure what’s up. Maybe my ISC is sticking cause after sitting for a bit it’ll slowly creep back up to ~850rpms. I got gas, and after restarting it the wine went away and idled o.k, but then I did another pull and it came back and started to idle bad again lol. does anyone run Mikie’s intank fuel pump setup? Or does everyone run the factory location? If so what pump are you guys running? thank you guys for your help! I really appreciate it. Also thank you Psu_Crash for getting me back on the road! 1 Link to comment Share on other sites More sharing options...
psu_Crash Posted November 13 Report Share Posted November 13 You're very welcome, really glad to hear it helped!! I run a Walbro 255lph in the stock location and it is also loud at times. I attribute it to getting warm after hard runs. As long as it has pressure, I'll continue to run it. I'm sure the MKS in tank is a great setup. I don't know anyone personally that is running it, but I will probably go that route when mine dies. What does the AFR look like when it's acting up? If it still looks good under load I can't imagine it's the pump. Double check the vacuum line to the FPR. Maybe test it for vacuum/pressure leaks just to be sure. I run my idle speed a little closer to 1k. Mainly because I fear that my cam and semi solid engine mounts will rattle the car apart at lower RPM. Turn the idle stop in a hair to see if it helps. Does it stumble off idle when it's running poorly or will it rev free? Link to comment Share on other sites More sharing options...
Ryan S Posted November 14 Author Report Share Posted November 14 2 hours ago, psu_Crash said: You're very welcome, really glad to hear it helped!! I run a Walbro 255lph in the stock location and it is also loud at times. I attribute it to getting warm after hard runs. As long as it has pressure, I'll continue to run it. I'm sure the MKS in tank is a great setup. I don't know anyone personally that is running it, but I will probably go that route when mine dies. What does the AFR look like when it's acting up? If it still looks good under load I can't imagine it's the pump. Double check the vacuum line to the FPR. Maybe test it for vacuum/pressure leaks just to be sure. I run my idle speed a little closer to 1k. Mainly because I fear that my cam and semi solid engine mounts will rattle the car apart at lower RPM. Turn the idle stop in a hair to see if it helps. Does it stumble off idle when it's running poorly or will it rev free? Ok, thats what I’ll probably get once they are back in stock at MKS. Just to be sure i always have pressure lol. I just have a Carter OE from Rock Auto. thats what I figured also as it only happened once I was doing some pretty hard pulls. I don’t remember what AFR’s looked like when it was acting up, under load AFR’s look great so that’s why I was hesitant about the pump being the culprit. I’m gonna double check all vacuum lines to see if one popped off and that’s why it idles weird at times. I’ll probably turn that screw in a hair to about 1k rpm’s too, peace of mind to have a little better oil pressure at idle. It depends what I do lol. If I let it sit and the idle comes back to normal it does great, when the idle dips and you quickly go again it also does great. And it doesn’t really run poorly it just idles very low at times. That’s why I was thinking something to do with the ISC like maybe it isn’t making good contact with the lever, or it’s sticking. whats weird is it only happened after the pump starting making noise after 30mins. Before that It did absolutely fantastic. I’m gonna take her for a spin tonight and see if the pump still makes noise and see what happens. thanks! Link to comment Share on other sites More sharing options...
Ryan S Posted November 14 Author Report Share Posted November 14 (edited) Update - took her for a drive after I got home from work and she runs fabulous. It never did the weird idle fluctuations, also the pump wasn’t screaming for help during normal driving. But once I did a couple pulls it started to make some noise but that’s probably normal. In the future I would like to do Mikie’s in tank system. Now I can take her to school and show off a little😉 and drive it before snow hits… anyway thanks again! Edited November 14 by Ryan S Link to comment Share on other sites More sharing options...
psu_Crash Posted November 14 Report Share Posted November 14 Sounds like you are good to go! At least for now 😉 Have some fun with it! Maybe the snow will hold off for a bit Link to comment Share on other sites More sharing options...
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