Hey there!

So I have a 1992 Dodge Daytona 2.5, non-turbo. I've turned it into a circle track race car, so some of it is stripped, but for the most part it is stock. I have a problem that just started. When under a load, the car does something that I can only describe as "poor throttle response" You can push the pedal, but that car just won't go, but eventually it will. It's very intermetant on when it decides to work and when it's doesn't. In neutral, the car can rev up with no issues. I'm not sure if it's related, but the tachometer, has also started to become very erratic, this is a new issue as well. Sometimes the tach will jump to 8k, and sometimes it will stay at 3k, again very intermittent, and only under a load.

New plugs, wires, distributor cap and rotor, ignition module, Throttle positioning sensor, timing is good. 42 psi on the fuel pressure.

Any ideas as to what I should look into next? Thanks in advance.

 

What are you running for an exhaust? Have you checked your vacuum pull on the engine? It should pull around 17 inches of vacuum. You can only pull a certain amount of air in if it isn't getting out. I'm sure you've pulled the cat. Are you running a muffler and how old is it. Is your garage near farm fields? You might have something simple like a mouse building a condo in your exhaust. Slap a vacuum gauge on that puppy and see what you find.

 

Exhaust is stock, the Cat is still there as well. New o2 sensor too. No mice, I've been all around the car, and I don't see any evidence of them. Where would I check for vacuum on this car? Is there like a port I would plug a vacuum gauge on to? (I know my local AutoZone has vacuum gauges I can get, but I've never used one)

 

I can almost bet your converter has collapsed inside. Look for a vacuum line around the throttle body. Look for a rubber cap on something like the manifold. I used to rally cross an '89 Omni and ran a vacuum gauge on it all the time to see what power reserve I had. If you can't find a blocked off port, get some vacuum line and vacuum adapters (little pointy splices) and put the gauge inline. You always want a vacuum gauge handy as it tells you how healthy the engine is.

This is the one I use.


The vacuum gauges you get now are a vacuum/turbo gauge if you want to put one in the dash. You can see what's going on with this chart.



Some of the details might not be applicable as this is from a troubleshooting guide I have from the 1930's. The basics though on non-turbo engines don't change. (When's the last time you saw an electric hand shifter?)

Since the exhaust is 30+ years old, I'm thinking either your cat. or muffler has collapsed inside. Raise the car and thump (<---fancy technical term) the bottom of the cat. and muffler. If you hear a rattle, it's rusty inside. If this is a dedicated race car, I'd swap the exhaust for a low restriction one. Find the problem area first though.

 

So I'm guessing I found the right spot to test the vacuum, because I did get a reading. It bounces though while the car is running, is that normal? Also, I knocked on the converter, took a video of it, here is a link. https://photos.google.com/u/2/photo/...lYogcmMZ5WISpC It didn't sound like anything you were describing.

 

Does it still have the check engine light? Any codes?

 

20 inches of vacuum is a healthy engine. As for the video, file not found. When it bounces, does it act like any of the illustrations on the chart I posted? From what I can see, it looks like you have the 4 banger. When was the last time the timing belt was changed. A sticky valve will cause a bounce in the reading.

 

Okay, let's try this, the forum doesn't let me upload a video. Here is me knocking on the CAT https://drive.google.com/file/d/1eL-...ew?usp=sharing and here is the vacuum gauge while running. https://drive.google.com/file/d/1qZl...ew?usp=sharing It looks like number 5 above. Seems to jump between 20-25

Yea its a 4cy. I've never replaced the timing belt so I'm not sure. It seems tight though and it was timed earlier this season, I'm not sure if it would have jumped timing? At idle, the car is really good, and revs up in neutral with no problem. There is no dash, so I don't have a check engine light.

 

Okay, th gauge is telling me there is an issue inside the engine. I'd do a compression check on the cylinders and after that watch the valve train as it's running. I don't think it's your converter or timing belt. I'm assuming you have the SOHC engine.

 

Okay. So when you say watch the valve train, what do you mean? Okay. I'll do a compression test on it. You think it's internal and not like electrical? It's weird to me that it works fine until there is a load on it. I can go around the track for the pace laps just fine. It's not until the green flag drops and it's time to go, that the car just won't go, but it will take off eventually but then after a lap, or even the next turn, it will not respond to the throttle, and the process repeats itself all over again.