rkvsmb

My car sometimes runs great other times when i start it it runs and idles good butwhen i take off it bogs out like its not on all cylinders what could cause this to only happen sometimes

davek9

Hello and welcome, please give us some back ground on your car, like how long have you owned it, what has been serviced, over all condition and mileage?

Some Pic's would be nice

thanks

Dave K

rkvsmb

I just got this on a couple months ago but the lady before me kept it up pretty well it has 110000 miles its automatic and runs strong usually just every once in a while it gets that bug and runs bad

James Bailey

It is probably running on 4 cylinders....your car has two ignition systems each drives 2 cylinders on each bank. Driving it in that mode will eventually break the drive shaft unless it catches on fire first...if you have the cat convertor the raw unburned gas from 4 cylinders will burn in the cat which turns red hot and ignites the undercoating burn up the firewall insulation and pretty much everything on top of the engine. Such a common occurrence that starting in 1989 Porsche added a exhaust temp monitoring system to shut off 1/2 of the fuel injection to those cylinders which were NOT getting spark.
That said coil wires (both of them) need to be checked for corrosion, caps rotors, and ignition secondary stages next to the hood latch.

dr bob

The car has two complete and separate ignition systems, so among the first things to check is that both systems are working correctly. The car will run fairly smoothly with one system disabled, it may just be way down on power. More than a few cars have burned as drivers continue to drive with one ignition failed, essentially pouring raw fuel through four cylinders into the catalysts. The cats overheat quickly, and burn through atou trans lines, undercoating etc, until interior pieces like sound deadening and carpet catch fire. It takes just minutes at driving speed, and if you are cruising you probably won't notice the power loss until your feet get hot.

Intermittent failures are hard to trace, but you can start off by confirming a few things. First is that the coil wires are firmly seated in both the coils and distributor caps. At the same time, make sure those wires are not contacting anything else on the way. If the car has original ignition components like caps/rotors/wires, it's past due for replacement of those pieces.

Go through the service history on the car, looking to see if/when the LH fuel injection controller was rebuilt or replaced. Failure modes include the symptoms you describe as the controller deteriorates, ultimately leading to a car that starts very hard, and runs poorly due to over-fuelling. There's a whole diagnostic process for the controller, but te simple question of whether and how it was replaced previously can eliminate it as a candidate.

The Mass Air Flow sensor (MAF) uses a heated wire filament to determine how much air is passing into the engine. Each time the engine is started, the wire gets a short burst of high electrical current passed through to burn off any oil or other contamination that might have deposited on the wire. Over time, the wire will fail due to the heat cycling. Before it fails completely, it will fall out of usable calibration range, giving erratic performance. The workshop manuals have a primitive test procedure, but the easiest and most accurate method of testing is to either swap in a known-good MAF, or send yours for testing. They can be rebuilt with a new platinum wire filament.

Fuel pump relay is a failure point. I had one fail with weak running leading up to total failure. Low fuel pressure was the symptom I saw. A new relay is cheap (<$10 from some suppliers), and should be replaced in your car now due to age. Look at replacing the LH (fuel injection) and the EZK (ignition system)relays at the same time. Some folks carry spares in the car "just in case"; I believe in installing the 'spares' in the comfort of the garage rather than along the side of the road somewhere, so in they go right away. Carry the old ones as spares if you must.

Clean all the ground points associated with engine management. It's a good idea to clean all of them as part of an annual PM ritual that covers the battery and other possible electrical failure points. More than a few intermittent gremlins have been solved with a brass brush and a 10mm socket.

rkvsmb

Thanks i will try to do a little maintenance would it be wise to bypass the catt now with a test pipe

dr bob

I recommend finding and fixing the problems quickly. If it is in fact running on just four cylinders, there are other driveline concerns that crepp up. The fracture of the driveshaft is a big one. Leave the catalysts in place so it will be OK to inhale in your neighborhood. We had a clinic car here over the weekend that has no cats installed. I had almost forgotten how really stinky that cars are without cats, even ones that are well tuned and maintained.

rkvsmb

Ok so i have replaced the ignition relay and so far so good can this be what was effecting it

Mongo

It could have been mostly likely the cause of the problem. Another good piece of advice for you would be to pull the airbox on the car and inspect/clean the grounds under it. I did this, and was quite surprised at how well the car ran after with some shiny copper ring terminals bolted to the block.