1991 Dodge Shadow Fuel Injection Questions

[KManiac]

I have a 1991 Dodge Shadow ES Convertible with 2.5 Turbo and 114,000 miles on the clock. The fuel system is original. I encountered a drivability problem where, if I mash the throttle, it will start to accelerate to a point, then buck and snort like it is starved for fuel. Back off of the throttle and is runs just fine. Normal driving and acceleration shows no problems.

My Haynes manual states that I should have 55 psi fuel pressure at the fuel rail. I put a test gauge at the fuel rail and measured 50 psi. I put the test gauge between the pump and fuel filter and measured 55 psi. I replaced the fuel filter on general principle. Again, I measured 50 psi at the fuel rail. When I increase the engine speed, the pressure will spike up to 55 psi then fall back to 50 psi.

I then installed a new fuel pressure regulator, an after market unit. I started the car and measured 48 psi at the fuel rail. That didn't seem to help, so I put the old one back on. Now it is back to 50 psi at the fuel rail.

The Haynes manual isn't that helpful beyond that. Could it be that both my original and after market replacement pressure regulators are both not up to par, or is there something else I am missing. And what about my fuel pump? Does the output pressure at the inlet of the fuel filter seem reasonable or is there something I am missing? Any insight into this situation would be greatly appreciated.

[KManiac]

Well, I learned a little bit more about the car today. I disconnected the vacuum line to the fuel pressure regulator and installed a vacuum gauge to measure the sourse vacuum. I then connected a vacuum pump to the regulator itself.

I measured 20 in.hg. of vacuum at the vacuum line to the regulator, at idle. Opening the throttle caused a momentary drop in vacuum, which quickly stablized back to 20 in.hg. I would expect that lower manifold vacuum measurements with the car driving down the road and under load.

With 0 vacuum on the regulator, I measured 60 psi fuel pressure at the fuel rail. When I drew a 10 in.hg vacuum on the regulator, I measured 55 psi at the fuel rail. When I increased the vacuum on the regulator to 20 in.hg. (same as the manifold sourse), I measured 50 psi at the fuel rail. It appears that maximum fuel pressure on the rail is 60 psi and the pressure drops 1 psi for every 1 in.hg. of vacuum applied to the fuel pressure regulator.

Does anyone out there know whether or not these measurements are normal for this set up. My Haynes manual is deficient in this regard. Any help here would be appreciated.

[billjade]

i had the same problem with my shadow i think iits the vaccum to the turbo check your lineto the hall effect when it over boost s it will shut down.

[KManiac]

Thanks for the advice. This is not the case, this time, however. I encountered the same problem you had about four years ago. The turbo gauge would peg out most of the time. Then, under heavy acceleration, it would either start to ping or the ignition would cut out completely. I drove it for about a year and a half this way. The dealer diagnosed it as a bad vacuum line to the wastegate and repaired the line. Then the service manager tried to sell me a new turbo at the tune of $1,800. I told him to take a hike. Three years and 25,000 miles later (114,600 miles total) the turbo still works great.

Although the extra power from the overboosting turbo seemed great at the time, the extra power output from the engine had a negative effect on the automatic transmission. Shortly after the turbo repair, I fragmented a clutch disk in the front clutch pack, spraying metal fragments throught the transmission and causing it to stick in high gear. I had the transmission rebuilt for the same amount as the quote for the new turbo. Good thing I got a three year warrantee. A year later, something else came loose inside the transmission, jamming the rear planetary set and ripping the splines out of the center hub. I got it rebuilt again at no charge. Clearly the overboosting engine overstressed the little torqueflite to the point of destruction.