Boost Level, TPS or throttle cable related?

[tommyturbo]

I've been doing some searching here, but haven't found anyone with too similar of an issue. I've got a 87 Daytona Z with the old school log intake turbo I set up and auto. It runs well, no codes. I got a computer from Cindy for it shortly after I picked up the car. I'm comparing this car to my 86 GTS with the same log intake turbo I and auto trans, same computer set up.

The GTS has a very linear feel to the boost as you increase throttle, has good mid throttle response. It feels really strong. However the Daytona will not boost above about 5-7 psi unless you mash the gas into the carpet, then I can get full boost up to the 14psi limit of the computer. It feels like is it is all or nothing with this car, if I mash the gas to get more than 5-7 psi of boost the car is frantic fast and will downshift usually unless your already at highway speed. There is no mid range. Light cruise or mash the carpet full on go.

Cable doesn't look bad, or seem to have slack in it...but seems like it might be the obvious thing. Would consider a different TPS, but all the TPS for a log car I see on rock auto, autozone, etc all have a 3 wire pigtale, this one has a plug connector like turbo II and later cars, but is not the same style as a T-II TPS. Some of my searches on here about the TPS related to somewhat similar symptoms. So where can I find this style TPS?

I'm pretty sure it's the computer keeping the boost level low, because if you quickly open the throttle midway, the boost comes up quick to like 9, but is quickly backed off to around 5-7.

Open to ideas, sorry if it is a dumb question.

[turbovanman²]

How is the trans? Have you tried an MBC to see if its the computer controls or the vacuum routing for the wastegate? Any codes?

[1BADVAN]

that's what it is supposed to do, if at part throttle the computer limits the boost, you can have the computer re-programmed or use a manual boost controller.

[tommyturbo]

Trans seems perfectly fine, shifts well. All vac lines are in good shape. Car is low milage and in good shape. Computer will control wastegate if I mash the gas to the carpet it goes to 14 psi (what the fwd logic modle is set to) and car pulls fantastically. I can't seem to get a mid range. It's low boost or max boost, no in between. Would think if there was an issue with vac lines or solenoids it would not be able to maintain the 14 PSI at wot and would spike past and shut down. I can bury my foot in the carpet and it will hold 14 just fine. So I like to think all the lines and wastegate work. No codes.

On my other cars the boost is relative to throttle, so more throttle more boost, and I open throttle mid way and get 9-10-11 etc PSI. This car from zero to 90% throttle and I can't get more than 5-7, mash the gas the last bit and I get 14. NO in between.

And I've been using the other cars as a comparison. The 86 GTS is identical in set up. Drove them back to back last night and could tell the difference. The GTS doesn't have a boost gauge, but it felt way better than the daytona . Any of my turbo II type cars will boost in a linear way, boost will climb relative to throttle.

When I first got the car it had a mopar performance logic module, and that one seemed to be set around 10-11 psi, and it felt more linear, but the car seemed to run ruff with it, after swapping in the fwd logic module, it runs way smoother and controls the AIS much better.

[tommyturbo]

Took a pic of the TPS, as I am tempted to try swapping it. It's unlike any of the T-II style, and all the parts stores show it having a wiring pigtail and spade type connectors. Looked over vac lines again, all look good. No codes, just 55. I'm not looking to do wild mods like most folks here, just stealthy mods that make a bit more power with no visual signs, I'm much more about restoration / preservation.

[mpgmike]

Sounds like a programmed strategy. Check with Cindy. It may be that was intentional by whomever programmed your LM. You can check your TPS with an analog volt meter. With Key-On engine off, gradually open the throttle with your volt meter tied to the signal wire (usually the middle wire). You should see a smooth sweep between about 0.7 volts and about 4.5 volts. If there are any glitches or hick-ups, you have a bad TPS. If not, replacing a good TPS with another good TPS won't fix your issue.

Mike

[tommyturbo]

I emailed FWD but have gotten no response.

[trannybuster]

Have you done any work to the car..?...or just swapped computer, sounds like you just got the car if your not sure how it use to run, or should run. Check the dist timing as well as cam timing, I would bet dist timing, if computer is cutting boost its going to cutout, but sometimes they change this on Vendor cals so cutout isnt so hard..

[tommyturbo]

I only know car since I have had it, which is a short time. It's a clean low miles car. Checked cam and distributer timing, all is perfect. I did do plugs/wires, fuel filter, stuff like that. Car came with a mp computer, and it tended to be rough running at idle, and had a hard time controling the ais when cold. Swapped the computer to the one from cindy, and car runs smoother, has no more ais issues, gennerally seems to run better. ONly difference is the mp computer seemed to have a more gradual linear feel and boost seemed to be maxed out around 10-11 psi. Cindys will max at 12-14, but to get above 5-7 I have to really go heavy throttle. I've been comparing this to my 86 GTS because it has the most similar engine, intake, computer, trans set up.

[trannybuster]

^^ I see..whats the timing set at 12* or 14*....does it have issues when coming to a stop? If the speed sensor is acting up it will give the car fits and limit boost, and will not throw a code.

[tommyturbo]

it's at 12*, no codes, and no issues with coming to a stop. Speedo works, as do all trip computer distance funstions.

[trannybuster]

The speedo will work, but that doesnt mean the speed sensor isnt dodgy...

[tommyturbo]

understand, but it does seem to be working ok.

[trannybuster]

plus as you said th distance computer works...