A friend has a 1990 Cad, I think it's a fleetwood. It has the 4.5 V8 and front wheel drive. The car only has 41,00 miles. It ran good a few months ago. He didn't drive it for a while and when he started it, it didn't want to idle or run very well. He said it bogged and ran real rough. The way he described the problem I thought it might be a clogged fuel filter. I changed the filter but it didn't help. I don't have the manual for the car. I need some help in diagnosing the problem and displaying the trouble codes. I have the manual for a 1984 and 1985 will the trouble code display procedures in either of those manuals work on the 1990? Also, this car has a throttle body that looks entirely different from my 1985. I think the problem may be a leaky injector but I can't see the injectors in the throttle body.

Please help.

I think you migh pull the codes the same on both the '85 & '90. Try it.

Does the 4.5 have the EGR tubes in the TB like the 4.9? If so, rod them out if they are full of carbon.

Might be time for new plugs, wires and distributor cap.

the 90 4.5 is mpfi so you wont see injectors in the tb. pull the codes and post them

Thanks, fellows. I'll check the dist & wires and try to pull the codes. I'll post again in a couple of days. :stirpot:

Hi fellas. I checked the dist and wires. They need to be changed sometime in the future but they are not causing my problems. I was able to display the codes, E74 showed up. I don't know what E74 code means, help.

Also, what do you mean when you say the car is mpfi? I'm not familiar with that term. Thanks. :worship:

MPFI means multi-port fuel injection. It just means there is an injector for each cylinder instead of the fuel being injected through the throttle body. You'll see them on the fuel rail going into the intake manifold.

E74 is MAT Signal Interrupt. It means the manifold air temperature sensor changes 7 degrees or more in 250 milliseconds (basically your MAT sensor is fudged). So basically, you either have a problem with the MAT sensor, or the wiring going to it... It's also possible it's a connection to the ECM, but not likely.

The MAT sensor is mounted on the intake manifold. If you're looking under the hood, It should be toward the left and back a little from the throttle body...near the back-left injector. There will be a wire harness plugged into it...well hopefully lol.

EDIT: Yes Ranger, the 4.5 has the EGR tubes under the throttle body...so yeah, make sure those tubes are not clogged. Just open the blades up and you'll see them coming up from the manifold.

Thanks, TAILFIN. Would a faulty mat sensor cause my problem?

It might. The computer takes the MAT sensor (among others) input into account when it calculates the fuel to be delivered. I'm not sure if it would be enough to not allow it to start, but it's possible, and would explain the roughness before. Regardless, it sounds like that is an issue, so I'd take care of that, and if it still doesn't start, come back here and let us know so we can ponder lol.