Runs for 10 miles then gradually fails

[Dan Foltzer]

Bought a '91 Reatta with 73K miles. Starts up & runs great for about 10 miles then starts bucking, gradually getting worse until it is barely running.  After running around 3 miles, shutting the key off & restarting, it does the same.  Replaced ICM, MAF, coils, wires...even the fuel pump.  Diagnostics show no codes except 552 for disconnecting the battery. Any help would be appriciated 

[2seater]

What is the actual fuel pressure and was the filter changed at the same time? The other possible concern is a restricted exhaust system, collapsed baffle in muffler or clogged catalytic converter. No mouse nest in the intake plumbing or air box?

Edited October 5, 2023 by 2seater

[DAVES89]

The other thing to consider is that you have very low miles and may have sediment in the tank that is stirred up and clogs the fuel system. Car is then turned off sediment settles down again and the process starts over again.

[2seater]

Well, that’s a series one L27 engine, so some of the potential vacuum leaks aren’t an issue, like the pcv for example. Gradual loss of power would seem to indicate a buildup or steady decrease of something over time. Does it run differently with the power loss, such as rougher running like losing one or more cylinders, or just like it is laboring more? You may need to install a long hose on a fuel pressure gauge so you can see it under load. Are you familiar with the built in diagnostics? You can monitor several engine parameters while underway. I saw the mention of rerouting rear plug wires making some improvement which is curious.

[Dan Foltzer]

Your comment about a gradual increase in something got me thinking.  I moved the plug wires that go to the left bank because the intake plennum is a lot hotter than expected.  The exhaust is super hot at the tailpipes so I guess the catylitic converter is operational but noticed that there is more pressure cold than hot.  D you think a partially clogged muffler could cause the intake plenum to be so hot, maybe causing vapor lock?

I appriciate your input.

[2seater]

A fuel injection system should not vapor lock in the conventional sense. The fuel is under 40ish pounds of pressure and is constantly flowing through the fuel rail, so it should not allow any bubbles to accumulate. The pressure regulator is on the drivers rear top of the engine and the pressure test connection is located there as well. I would get a gauge on it and see what it is doing. First thing.

 

I don't know how to determine if the intake is hotter than usual? Temperature gun? The intake does not use EGR like the earlier models so there is no direct exhaust to intake manifold connection to heat things up. A restricted exhaust will probably tend to keep more heat in the engine in general I would think so it may have some effect? I do not know. The standard way to check for backpressure is to remove the O2 sensor and install a pressure gauge. You can just remove the O2 sensor and run the engine to the normal point of failure to see if it makes a difference but of course it will be very loud and items in the area need to be protected from the escaping hot exhaust. Last resort? 

 

Running lean will tend to be hotter as well as retarded ignition timing. Some items will not set a code that is why getting familiar with the diagnostics may be helpful.

[Ronnie]

14 hours ago, Dan Foltzer said:

Bought a '91 Reatta with 73K miles. Starts up & runs great for about 10 miles then starts bucking, gradually getting worse until it is barely running. 

I ran into a similar situation with a '91 model S-10 pickup. It had a 4.3 engine with throttle body injection. It would start running poorly and then finally die after 10-20 miles of driving on the interstate. After sitting for a few minutes it would start back up as if nothing was wrong. Then it would repeat after driving more.  One day it died on the ramp coming off the interstate at a gas station where I was going to fill up with gas. When I removed the gas cap to put fuel in I heard a loud sucking sound as I removed the cap. The gas cap on it had a check valve in it that is supposed to let air in but not allow fumes to go out. The check valve in the cap was stuck causing a vacuum in the gas tank. I replaced gas cap and the problem went away. The next time your '91 starts acting up, check the gas cap to see if you have the same problem.

[Dan Foltzer]

Thanks for that.  I did consider a bad gas cap. The first time I drove it to a gas station, it ran great, filled it with premium gas & barely made it home.  Heard no sucking sound but the intake manifold was unusually hot.  After cool down (over night) I left the gas cap on loose but the problem persists.

[Ronnie]

1 hour ago, Dan Foltzer said:

The first time I drove it to a gas station, it ran great, filled it with premium gas & barely made it home.

Maybe there was water in the gas you filled it up with. My wife filled up with gas that had water in it one time and the car would hardly run.