Studder Boy

[Shark Pilot]

I have a 1982 DMC with a DPI exhaust and DPI cams in it. Took it to PJ Grady to do the exhaust install and fix a number of issues created by the previous resto job. He did an amazing job, but I have questions about a studdering issue I'm having and wondering if there is anyone out there with the previously mentioned combination on their car? From 0-40% throttle I get this weird studdering like the car isn't getting enough fuel or isn't firing correctly. Then at or about 40% to 100% throttle the car just takes off like it's turbo charged with great smooth power application and no hesitation. At idle it lopes properly with Josh's cams at around 900 rpm.

I've tried to adjust the CO (and consequently the idle control) to as high as a half turn more fuel to no avail. Just ended up with crappy gas mileage and a stinky exhaust. Then backed it off to where Rob Grady set it with a 1/8 turn less fuel (and another idle adjustment). With this adjustment it runs faster with better gas mileage, but still at the 0-40% throttle range studders consistently. Any thoughts? I find this issue incredibly annoying.

Patrick :tantrum:

[Project Vixen]

By chance was this previously a turbo'ed car?

Just offhand, it sounds like it could be an ignition timing or vacuum advance issue.

[Denverdelorean]

I concur on checking the vacuum advance

[David T]

I concur on checking the vacuum advance

It may take a little more than just checking the vacuum advance. Even if it is working it may not be coming in fast enough (or at the correct time) for the hotter cams. You need to check with DPI for their recommendations on initial timing and how to set up the mechanical and vacuum advance. Of course it can't hurt to make sure the timing is set and both advance systems are working.

[krs09]

I have a 1982 DMC with a DPI exhaust and DPI cams in it. Took it to PJ Grady to do the exhaust install and fix a number of issues created by the previous resto job. He did an amazing job, but I have questions about a studdering issue I'm having and wondering if there is anyone out there with the previously mentioned combination on their car? From 0-40% throttle I get this weird studdering like the car isn't getting enough fuel or isn't firing correctly. Then at or about 40% to 100% throttle the car just takes off like it's turbo charged with great smooth power application and no hesitation. At idle it lopes properly with Josh's cams at around 900 rpm.

I've tried to adjust the CO (and consequently the idle control) to as high as a half turn more fuel to no avail. Just ended up with crappy gas mileage and a stinky exhaust. Then backed it off to where Rob Grady set it with a 1/8 turn less fuel (and another idle adjustment). With this adjustment it runs faster with better gas mileage, but still at the 0-40% throttle range studders consistently. Any thoughts? I find this issue incredibly annoying.

Patrick :tantrum:

I had the same issue to the T. It turned out my mix was way off. It would stumble on light acceleration (bad, like it was starving for fuel) but run good on hard acceleration. Although when it was warm it did run ok, just real bad when it was cold.

[Shark Pilot]

I had the same issue to the T. It turned out my mix was way off. It would stumble on light acceleration (bad, like it was starving for fuel) but run good on hard acceleration. Although when it was warm it did run ok, just real bad when it was cold.

So which way did you go with the mix? Some quick history to those who have responded, it was always a non-turbo'd car. Was going to do the Stage II DMC upgrade, but they rape people on price so I did it through Bauerle Automotive. Turns out he put Josh's cams in my engine and it DOES add a ton of power and he did it for about $1600 less than DMC which was nice.

I put a half turn more fuel (at the highest as I had other settings in between 0 and 1/2 trying to get rid of studder) from where Rob Grady set it two months ago and like I said it didn't do anything except slow the car down a little, decrease my fuel mileage and make the DPI exhaust stink really bad. Then I backed it off to 1/8 turn LESS fuel from where Rob set it and my fuel mileage went up, performance went up and stink went down. However, SAME PROBLEM. I'll look into timing. Haven't gotten a call back from Josh at DPI yet, but I'm still working that. I'm assuming this is NOT normal operation. Just seems weird to have it studder like this at less than 40% throttle applied. Before Rob got a hold of it I had studdering on accelleration in all gears and the mix was too rich. He corrected a TON of vacuum leaks and mix issues that I had nothing to do with. Car runs now as I've mentioned. I'm SO close to having this thing trimmed out well, just can't get this fix for some reason.

Where the CO sits now there is NO WAY to back off more fuel because it will simply stall even with an idle adjustment. It's like I've got it set to the perfect point of no return on less fuel so i know the current setting is THE setting for fuel delivery.

Also note, I have brand new injectors, 8mm high voltage silicone ignition wires and a 40,000V ignition coil and stainless fuel lines. The fuel system is in VERY good shape and hot/cold starts are right on so my accumulator is holding pressure always.

Patrick

[krs09]

So which way did you go with the mix? Some quick history to those who have responded, it was always a non-turbo'd car. Was going to do the Stage II DMC upgrade, but they rape people on price so I did it through Bauerle Automotive. Turns out he put Josh's cams in my engine and it DOES add a ton of power and he did it for about $1600 less than DMC which was nice.

I put a half turn more fuel (at the highest as I had other settings in between 0 and 1/2 trying to get rid of studder) from where Rob Grady set it two months ago and like I said it didn't do anything except slow the car down a little, decrease my fuel mileage and make the DPI exhaust stink really bad. Then I backed it off to 1/8 turn LESS fuel from where Rob set it and my fuel mileage went up, performance went up and stink went down. However, SAME PROBLEM. I'll look into timing. Haven't gotten a call back from Josh at DPI yet, but I'm still working that. I'm assuming this is NOT normal operation. Just seems weird to have it studder like this at less than 40% throttle applied. Before Rob got a hold of it I had studdering on accelleration in all gears and the mix was too rich. He corrected a TON of vacuum leaks and mix issues that I had nothing to do with. Car runs now as I've mentioned. I'm SO close to having this thing trimmed out well, just can't get this fix for some reason.

Where the CO sits now there is NO WAY to back off more fuel because it will simply stall even with an idle adjustment. It's like I've got it set to the perfect point of no return on less fuel so i know the current setting is THE setting for fuel delivery.

Also note, I have brand new injectors, 8mm high voltage silicone ignition wires and a 40,000V ignition coil and stainless fuel lines. The fuel system is in VERY good shape and hot/cold starts are right on so my accumulator is holding pressure always.

Patrick

First I did check all other options (timing,vac leaks,inj spray pattern,ect) then I started playing with the mix. I started the car and let it warm for a few min (not nearly as long as dave from dmcmw asked but..) then I just adjusted the screw all the way left till the she ran like shit then all the way right till she sounded like it was gonna stall and found a spot right in the middle, maybe just a shade rich. There was some fine tuning (turning it off and checking again, letting it get nice and hot (fans cycle on and off) and check again) but after a few adjustments its night and day. Starts better and is drivable right on start up, no more waiting. Smells better too!

[Shark Pilot]

First I did check all other options (timing,vac leaks,inj spray pattern,ect) then I started playing with the mix. I started the car and let it warm for a few min (not nearly as long as dave from dmcmw asked but..) then I just adjusted the screw all the way left till the she ran like shit then all the way right till she sounded like it was gonna stall and found a spot right in the middle, maybe just a shade rich. There was some fine tuning (turning it off and checking again, letting it get nice and hot (fans cycle on and off) and check again) but after a few adjustments its night and day. Starts better and is drivable right on start up, no more waiting. Smells better too!

I think you and I have done the same things and achieved the same results. It MUST be something else because the mix seems really good and really, the CO is more about base idle anyway and less about performance. I thought it might have something to do with performance though (because I'm a new-ish DMC owner) and if its WAY off, it does, but in my case (and yours) I'm where I need to be in this regard. I should specify that the "studder" as I call it is when I'm around 2400 to 2800 rpm with 40% throttle or less, but AS SOON AS I step harder on the gas, above the 40% mark, there is NO hesitation and the car just moves out. I don't have to stomp on it, it's just above that mark the studder goes away. Maybe a timing issue. One problem I have is the oil dip stick won't seat properly and sticks out about 1" from the base tube. Could this be considered a vacuum issue and affect the car?

[Shep]

I also have this same setup (SPEC I exhaust and DPI Camshafts) on an automatic, and I believe I had this issue early on if I remember correctly. Took it back to DPI to get it repaired (it was under warranty at the time, opting for the full-off resto route), and he tweaked a few settings and got it to purr like a kitten... or more accurately, roar like a lion! ;)

For what it's worth, I would take it back to PJ Grady and have him fix the issue. Or just call him and/or DPI Josh to see if someone can diagnose it remotely. Either way, ever since I've gotten it fixed up, it's been smooth sailing and is a great system to have, haven't had to mess around with it since. :thumbup:

[Delorean Industries]

Pat, rob mentioned today that you were going to call. Didn't see the missed call though. Only way to tell for sure is by checking the cam prefix on the left shaft to know for sure if it is one of our grinds. We have never sold anything performance related to the shop mentioned as the installer of the cams. They may be ground by copying a set of ours onto a stock lobe set. If not indexed properly the cam can be advanced or retarded depending on set up. I know where and when every set we have produced is currently. All are accounted for.

At the very least you are dealing with a mixture concern. Setting the co is the first step to getting your running issues corrected.

[Shark Pilot]

Pat, rob mentioned today that you were going to call. Didn't see the missed call though. Only way to tell for sure is by checking the cam prefix on the left shaft to know for sure if it is one of our grinds. We have never sold anything performance related to the shop mentioned as the installer of the cams. They may be ground by copying a set of ours onto a stock lobe set. If not indexed properly the cam can be advanced or retarded depending on set up. I know where and when every set we have produced is currently. All are accounted for.

At the very least you are dealing with a mixture concern. Setting the co is the first step to getting your running issues corrected.

Josh thanks for the response. I'll try you again Monday. The car will go back to Rob around March and I know he has his own DMC with the same setup that he'll be tuning out in the next 4 weeks. I can live with the studder for now. I have the sheets that explain the type of cams used and it's possible that they aren't yours, but I'll have to go back home and make sure. I think what might have happened was the cams were COPIED from your exact specs. I have some other stuff for Rob in the spring anyway. If the cams are indeed the problem and they were not copied well you'll be getting an order from me (or Rob) around the spring time. The exhaust is amazing by the way. I mean, THIS is how the De Lorean is supposed to sound so good job engineering that system. :notworthy: It's a bit loud in the cabin, but better than the garbage I had on there before. Wish I had the $$ for that amazing twin turbo setup. :headbang: I'll be in touch.

[Delorean Industries]

Sounds good! Glad you like the system! Call anytime. Just to clarify as I really don't want to be vague on this. Quality control is everything especially with products that require skill and knowledge above general repair. With this said unless you purchase a component from DPI or PJ Grady and or have a DPI SPEC component installed by one of us there is no guarantee the component origin. At this time Grady is the only authorized dealer/installer of our products. Our pricing is the same on components back and forth as well. No need to price shop as we advertise each others products for the same price. If your car is being serviced at Grady's and you want a DPI SPEC component simply tell Rob. By the off chance it is not in stock DPI will send what ever it is with free shipping.

[Shark Pilot]

Sounds good! Glad you like the system! Call anytime. Just to clarify as I really don't want to be vague on this. Quality control is everything especially with products that require skill and knowledge above general repair. With this said unless you purchase a component from DPI or PJ Grady and or have a DPI SPEC component installed by one of us there is no guarantee the component origin. At this time Grady is the only authorized dealer/installer of our products. Our pricing is the same on components back and forth as well. No need to price shop as we advertise each others products for the same price. If your car is being serviced at Grady's and you want a DPI SPEC component simply tell Rob. By the off chance it is not in stock DPI will send what ever it is with free shipping.

I have a good relationship with Rob and I trust him. When I picked my car up from him 5 weeks ago he had 17 De Loreans at his place. 17!! and it's JUST him. He's like a fricken cylon. Anyway, I've asked him about your products as I peruse your site weekly dreaming about more crap to put on my car and he states what you said above so I'll just get all your stuff through him. Looking for the stainless hood cover hinges right now. We'll sort this studder issue out and if I have to get him to REPLACE the cams in there now because they turn out to be non-DPI cams, we'll do that around March. If they ARE I'm sure he'll sort out the issues with it by discussing it with you or figuring it out himself. Thanks Josh. :wave2: