95 Riv Stutters under load Help

Recently my 95 Riviera supercharged has been having a huge issue where it stutters very badly when accelerating and going uphill. This problem doesn't occur when at slow speeds but when I reach about 45 mph or accelerate to fast it stutters and misfires like crazy. I took the car in to have it looked at because I thought it was a transmission issue but the mechanics said it seemed like an ignition or maybe a fuel issue. They hooked the car up to a scan tool and it showed a number of codes that were tripped. The strange this is that the CEL is not on and some of the codes that were displayed are from things I have recently replaced. Here is a list of the codes:

PO1640 and 1650 Boost Solenoid which I replaced.
PO131 and 132 O2 Sensor I replaced the manifold sensor less than 3 months ago.
PO1350
PO1351 PCM
PO501

The shop also said there was 4 codes for O2 sensors, a TPS sensor and the Cam/Crank alignment sensor.

I am wondering if anyone knows where I should start with this issue without throwing a lot of money and parts at the car. Before this stuttering issue happened I had one issue where the car would not turn over like it was not getting fuel or spark but if I left it sit for maybe 5 minutes and tried again it would start up.

Any suggestions on what I should do or where I should start would be greatly appreciated!

Do you think you can start by clearing all the codes and obtaining a service manual?

And by the way what condition is the battery in, and have you (ever) cleaned the chassis grounds? Reason to start here is that when a bunch of sensors turn flaky all at once it's often the case the real problem is the chassis ground they are all tied to has become loose (rare) or corroded (often). Also it is sometimes the case that inadequate battery voltage causes a bunch of codes to be set at once. All you need is one dead or partly dead cell in the battery (there are 6 cells) to cause a problem. You can test the battery voltage with a voltmeter, should be like 12.4 volts just sitting disconnected from car fully charged. Less and you have a discharged or damaged battery. Then you charge it using a charger that runs on house current. If it still does not come up to 12.4 or so you found a problem.

I noticed you posted something about "cam/crank sensor" which caught my attention because the cam and crank sensors are two different things. I am not aware of one code for both. Do you think you might benefit from your own code reader? If you had one you would not have to guess. A problem is that your '95 has an OBD-1 computer through an OBD-2 style port. I suspect you could find a (used but good) reader on eBay at a reasonable price. Actron CP 9145 comes to mind.



Albertj

The battery is also new as of maybe 3 months ago so that shouldn't be an issue. I will recheck the battery connections to make sure they are clean and secure. Is the chassis ground underneath the back seat by the battery or is there another location?

When I talked with the mechanic he told me it was a sensor that keeps the cam and crank in sync I was thinking he meant the cam position sensor. I think I will pick up a code reader so I can monitor the computer a little closer. Thanks

matt beyer wrote:

The battery is also new as of maybe 3 months ago so that shouldn't be an issue. I will recheck the battery connections to make sure they are clean and secure. Is the chassis ground underneath the back seat by the battery or is there another location?

When I talked with the mechanic he told me it was a sensor that keeps the cam and crank in sync I was thinking he meant the cam position sensor. I think I will pick up a code reader so I can monitor the computer a little closer. Thanks

There are a number of grounds in the RIv, that is part of the problem.

One is by the battery in back. You must use the corret Group 79 battery with the vent piping, if you don't the fumes from teh battery corrode the electricals under the rear seat, not to mention rot out the floor.

There is another important ground behind the drivers side kick panel, and another (for the starter) under the hood on teh frame rail not too far fore of the motor mount. THAT one is prone to breakign when you try to undo it, you can fix it by drilling it out an putting a stainless bolt in its place and use anti-seize so it does not rust shut again.

Another ground is under the ignition module, under the coils. Before you mees with that one you have to get heat sink grease to cover the heat sink plate or else the plate will corrode (it is mill finish aluminum) and overheat, makign the module fail. actually come to think of it if someone took the coils off before and did not put them back properly with the insulator and everything, that could be contributing to your troubles...

There is at least one more ground on the firewall in the engine compartment.

I had this too. Turned out to be a coil problem, so that's my best guess.

Riv95SC wrote:

I had this too. Turned out to be a coil problem, so that's my best guess.

good idea - coil secondary is about 7000 ohms, primary is around 1-2 ohms. Check the coils for shorts. When one of my plug wires went bad (conductor broke) it ruined the coil it was attached to.

Albertj