Tip-in stumble...

[Tony Hanna]

...only does it when it's cold though. Once it's up to operating temp, it either goes away completely or it's so slight that I'm not noticing it. Whatever's causing it, it seems to be more related to throttle position than rpms. It stumbles right off idle, but also I can be cruising along at 2k off the gas, start to give it some pedal, and it will stumble, recover, and run fine. Initially I thought the tps might have had a bad spot, but I swapped it out with a spare last night and it acts the same. I'm going to swap the map sensor with a spare today, and check the plugs, wires, and rotor. Hopefully one of these will solve it. I'd appreciate any suggestions on what else to check.
Thanks,

[WVRampage]

Too much fuel.

[Tony Hanna]

Good call. I'll check fuel pressure and look for signs of gas in the vac line on the reg too. The engine (and computer) was swapped in complete out of a wrecked but otherwise untouched '89 Lebaron, so the fuel system is basically untouched atm. If it's getting too much fuel, something has to have failed. The only thing I've done to it was to swap in a 2.2 TII rail, injector harness, and injectors since the injector harness that was on the engine had a bad connector that was causing a constant misfire unless you held it in exactly the right spot. That shouldn't have anything to do with it though as the 2.2 TII and 2.5 TI injectors are rated the same.
Thanks,

[Una]

I had the same problem with my '83 SC back when it was running the 2.5 turbo engine.. Never did nail down the problem.

[Tony Hanna]

It's not really a big deal, it doesn't cause any major drivibility issues or anything, it's just more of an annoyance. I know something isn't quite right and it bugs me. Plus little annoying stuff like that, exhaust rattles, interior squeaks and rattles add up to the point where a car just isn't fun to drive anymore. I like to try to stay on top of that crap and fix it as I notice it. Hopefully I'll be able to track it down. Gonna go through the ignition system tonight and try to rule that out as a possible culprit.
Thanks,

[unluckyty]

Possibly a sticking TB.

[Tony Hanna]

Possibly a sticking TB.

Shouldn't be. When I swapped tps sensors, I actually swapped the entire throttlebody because I couldn't get the tps screws loose on the old tb.
I cleaned the replacement tb up good and it's pretty smooth.

To recap, so far I've tried tps, hep, cap, wires, and rotor. The plugs are recent, and the one I pulled looked good. The ignition stuff seemed to help a little, but the problem is still there. If I can find my fuel pressure guage and timing light I'll check fuel pressure and ignition timing next and then try a different coil and map sensor. If none of that gets it, I'm out of ideas.
Any thoughts?
Thanks,

[ssheen]

Tony, my 88 Daytona Shelby does the exact same thing as well. I have never been able to fix it. I have thought it was because of too much fuel when it is cold. My fuel system is stock though other than a Walbro 255 and AFPR. If you solve your problem, please post your solution. I am very interested.

[Tony Hanna]

If I ever manage to figure it out, I'll definately post what I find.
If I had an adjustable fuel pressure regulator, I could test your theory about being too rich when cold by turning the fuel pressure down to see if the stumble would clear up.
Thinking about this from the fueling point of view makes me wonder if the coolant temperature sensor might not be the problem. I wonder if the resistance vs. temperature can change with an older sensor? If a sensor problem was causing the computer to think the engine is colder than it really is, then it stands to reason that it would be overfueling. Anybody have a chart that tells what resistance a cts should be for a particular temperature? I guess there's another thing to add to my list of parts to throw at it.
I'm glad I'm a packrat. This would be getting expensive if I didn't have spares of everything.:)

[ssheen]

Ever figure it out Tony?

[Tony Hanna]

Sure didn't.:(
It's been pretty chilly lately, so I've been letting it warm up for a few minutes before driving. Since it only happens when cold, I haven't noticed it lately and sort of forgot about it.:o
It's started making some really scary bottom end noises on a cold start that I need to look into before anything else, but once that's taken care of, I'll eventually get back around to trying to sort out the stumble.

[ssheen]

thanks for the update Tony. Do you run a custom cal?

[Tony Hanna]

I'm still running the stock '89 2.5 TI auto computer that was in the Lebaron that the engine came out of. I'll probably go to a custom cal eventually, but I don't have enough done yet to justify it. Still running a non-intercooled mitsu at close to stock boost for now. Everything else is on hold until I get this bottom end noise sorted out.

[iTurbo]

My Spirit R/T does this as well. Still haven't found the problem and the OTC says everything is fine and TPS output is very smooth and consistent. It stumbles only at very light throttle input and cruise. If I accelerate suddenly and let off the gas to resume cruising, it will buck and/or surge. Very annoying.

[Tony Hanna]

My Spirit R/T does this as well. Still haven't found the problem and the OTC says everything is fine and TPS output is very smooth and consistent. It stumbles only at very light throttle input and cruise. If I accelerate suddenly and let off the gas to resume cruising, it will buck and/or surge. Very annoying.

Does it only do it when cold or all the time? Mine straightens out after it starts to warm up.

[iTurbo]

Mine does it all the time, but not quite as bad when it's warmed up. I have another stock TB I'm going to swap on just to see if it makes a difference.

[Tony Hanna]

Hey ssheen,
you said you have an afpr right?
Would you care to try cutting back your fuel pressure a little at a time to see if it makes the stumble go away? Obviously try to stay out of boost while you're testing. definately don't want any engine damage due to lean out under boost. If that stops it, then the permanent solution would be as simple as pulling some fuel in whatever table the cal uses for cold run. I'm sure the guys that do their own cals would know how to go about it.

[ssheen]

Hi Tony,

Yes, I do have an AFPR. I will try that experiment. Now if I can only remember which way to turn it to lower. :D

Update: I change a few things this week-end. Just tested it out today when I came home from the gym. -10C, which is cold enough for the problem to show. However, today it did not. I changed the HEP to a spare. Changed the coil to cap wire to a new one. Put the cam timing back to 1 degree advanced from 6-7 degrees. Suppose to get colder yet. Will see how it does tomorrow.

[ssheen]

My issue seemed to come to a head yesterday. It was ok cold, but after I turned it off and restarted it, it was not running well at all. I pulled a 22 and 47.

[t3rse]

if the accelerator pump values are off in the cal it will do this...i know you are running a stock computer, but you never know...

[Tony Hanna]

Could they be off just while it's cold and still in open loop, but fine otherwise?

[3Bar_Mopar]

Mine does a similar thing. I have stock cal, fuel system and everything.....When it's cold, if I give very light throttle, it will almost bog...you can actually hear the engine bog down a bit. If I open 'er up a bit, the car runs fine....then the problem disappears completely when the car warms up.

I think it's an over fueling problem, as the A/F guage reads almost full rich during this ....maybe a combo of cold temps and 180 degree t-stat.

[Tony Hanna]

That sounds like my problem exactly. Wonder why the would have worked too much fuel in from the factory?

ssheen,
any luck figuring out your battery and cts codes?

[ssheen]

I thought it was an over fueling issue as well.

Well, I picked up a new sensor. It tested out close to the old one. At room temp ~21C the new one tested at 9.8 and the old at 10.5. In a cup of boiling water the new one was 2.8 and the old was 3.2. I threw the new one in the car. I test drove it this morning, and the problem was there a little, but only when cold like 'normal'. I do run a cal, though I have not changed it since the summer. I put the stock SMEC back in and so far the problem has not reappeared. Still need to test further.

I will test drive the stock SMEC again later tonight when the car is cold. If all is good, I will put the socketed SMEC back in and see what happens. If the problem comes back, I will try a stock cal and see what happens.

[Tony Hanna]

Cool man! Sounds like good progress. From that point it would just be a matter of figuring out what (accel pump values like t3rse mentioned?) in the cal causes it and what changes are necessary to correct it.:thumb:

[t3rse]

there is a different term for these computers, which I have no idea about, but you might be able to find out what it is from the d-cal page on yahoo groups...but anyways, my SDS has what is call "accel pump", which is meant to duplicate what carbs do, it just changes the pulse width under quick tps value changes, enrichening the fuel as needed to help with throttle response...i have found that leaner is better, as you are pulling from vac to boost and keeping the a/f around 13.1 until boost seems to make a big difference with off boost power...

[Tony Hanna]

Sounds reasonable. I just wonder how that's connected to engine temp. Surely the cal is programed to give a larger accelerator pump effect when the engine is cold and evidently it's a little bit overkill in some situations. That would explain the bog. So in theory, you'd want to lean the accelerator pump effect out a little when cold, but leave the stock values for when it's warm.
Make sense?

[jre97]

Tony,
The daytona did it when it was cold too. Could it be those before mentioned accelerator pump values. I mean we are running auto computers in 5sp cars. I wonder if the auto computer is a little richer when cold to compensate for the added load of a torque converter.

[Tony Hanna]

That's a real good question John. Wish I had a 5 spd 2.5 computer to test.
It could be that the added flywheel effect from the torque converter smooths the bog out so that you don't really notice it in an automatic.
It does bring up the question for those of you having this problem, what trans are you running, and what computer? I'm running a 5 spd. (520) with an auto computer.

[ssheen]

I am running a 555 with a manual cal.

[Aries_Turbo]

I dont think there is any difference for transient enrichment between the auto and manual cals. at least I cant see anything different.

here are the curves for both throttle enrich and map enrich. if there is a sudden change in pressure or tps volts the enrichment kicks in. these are just to show you what the curves look like.... not to use in a cal as these are my specific ones for a 2.5L.

Brian

[3Bar_Mopar]

I mean we are running auto computers in 5sp cars. I wonder if the auto computer is a little richer when cold to compensate for the added load of a torque converter.


Well, mine is an automatic car with an automatic cal...plenty noticeable.

[Tony Hanna]

I dont think there is any difference for transient enrichment between the auto and manual cals. at least I cant see anything different.

here are the curves for both throttle enrich and map enrich. if there is a sudden change in pressure or tps volts the enrichment kicks in. these are just to show you what the curves look like.... not to use in a cal as these are my specific ones for a 2.5L.

Brian

Wish I knew enough to play around with the cal. I'd try making some small changes and see if they had any effect.

[Tony Hanna]

Well, mine is an automatic car with an automatic cal...plenty noticeable.

Well, that shoots that theory.:)

[Aries_Turbo]

Wish I knew enough to play around with the cal. I'd try making some small changes and see if they had any effect.

its not that hard. there are some threads in the efi section where I wrote up some simple basics. http://www.turbododge.info/ has the process on how to socket the smec.

if you want to try, feel free to contact me and ill give you the info that i know.

Brian

[Tony Hanna]

Thanks Brian. I've got a smec laying around that I pulled apart and started removing the potting on. It's been buried since the move. I need to dig it out finish with the potting, desolder the chip and solder in a socket.
I get all that handled, dig up a burner, eraser, and some chips, and I'll probably take you up on that offer. The hardware I can handle, but programming is definately not one of my strong points.

[ssheen]

Tony, my issue seems to have resolved itself when I swapped coils.

[Tony Hanna]

That's interesting! Did you replace it with another stocker or aftermarket?
I think I've got a spare stock coil laying around here somewhere...

[ssheen]

I had an aftermarket on the car. I replaced it with the 19 year old stocker for now. My problem became really bad. I was lucky I got the car home today. Which did make it easier for me to find the cause.

[Tony Hanna]

What kind of aftermarket coil was it? I'll be upgrading the coil once I get some of the other stuff taken care of and get ready to crank up the boost. Sounds like I want to stay away from the one you were running.

[ssheen]

I had it on the car since December 2004. It is a Crane Fireball PS20. The mounting of the coil on the head may of been bad for it.

[Tony Hanna]

Yeah, I had one of the cheapie accel coils on my old Daytona. It was mounted to the engine too. Never had any problem with it, but then again it wasn't on there long. Definately sees more vibration that way though.

[gkcooper]

1. Remove your throttle body and clean it with some carb cleaner
(pay special attention to the edges of the butterfly and corresponding surfaces of the barrel)
2. Allow the engine to warm up until the fan cycles on-off once
3. Disconnect your coolant temp sensor (fan turns on)
4. Set your base timing to the correct indication
5. Adjust the adle set screw to the indicated rpms

If you still have tip-in issues after this it could be a result of a defective MAP sensor (plugged MAP line), Fuel Pressure regulator, sticky injector(s), clogged air filter, oil in intercooler, fouled spark plugs, defective plug wires, etc.

[ScottD]

What about a faulty coolant temp sensor also?

[Tony Hanna]

Thanks for the tips guys. John and I got the bottom end straightened out today, so I should be back to tracking this stumble soon.

[CSX321]

I know this is a really old thread, but I've got a very similar problem with the new engine in the '87 CSX. It had been running reasonably well for about a month, then two things changed: it got a lot colder, and at about the same time I dumped a can of Seafoam in a tank of gas. For about a week now, it's fine at startup, then at exactly the same place on the way to work it stumbles badly at tip-in for about a minute, then fine again until the next morning. I'm pretty certain it was right when it switched to closed loop. Today was different. It stumbled right away when I started it. Died several times in fact. Then, after it warmed up a bit, but not to operating temperature, it was fine, including the switch to closed loop. No codes.

It's got +40s, 3-bar, 255lph pump, S60 turbo (the one w/stock turbine side), running a cal from Rob. It's got a stock FPR on it right now, but I haven't actually checked the pressure yet. I don't know if the Seafoam triggered it, or something else.

Edit...It was fine at lunch, of course. I expect it will be fine on the way home, too, and not act up again until tomorrow morning. ¯\_(ツ)_/¯