Engine hesitation

ap911 · 02-14-2006, 07:03 AM

I am new to this forum having recently purchased an '84 Carrera with 99,000 mi. Under acceleration you can feel a hesitation in the engine. It is greater at low RPM and under load and above 4000 it is almost gone. In order to help solve the problem I have already replaced the distributor cap, rotor, wires, fuel filter, air filter and plugs all to no avail.
Plug #6 has a dry black (carbon) powder residue on it. The others are fine.
Could this be a valve adjustment issue? Esp. cyl. #6. I don't know when it was last done.
Could it be the air flow meter, oxygen sensor or head temp sensor and # 6 is only showing the effects.
Any other opinions?
Please help.

Also, if anyone can recommend a good shop in the Morristown, NJ area that would also be helpful.

lars63 · 02-14-2006, 07:08 AM

I'm sort of new to this forum too but welcome aboard wish I had some advice for your issues but don't worry there are plenty of people here that can help you out. Good luck

stlrj · 02-14-2006, 09:27 AM

Too rich will make it hesitate. Have your mixture reset to spec.

sergeshishik · sergeshishik's Garage

I'm no expert by far, but a valve adjustment if you can't determine when the last one was done should be a priority. Better yet do it your self, it is a bit dauntingI just did my first one just last month. This forum is awesome.

buster73 · buster73's Garage

Could be many things incl. the ones you mentioned. A valve adjustment certainly is a good idea anyway, if you don't know the service history. I would drive the car for a while and go through at least one gas tank with some fuel system cleaner added. Could be simply a dirty fuel injector or carbon build-up that might go away if the car is driven spirited. Otherwise you might have to go into error tracking mode and check ignition and fuel injection systematically. Best is to find a workshop who has experience with this year of cars. No need to re-invent the wheel. An unexperienced shop might waste a fortune in what hopefully is just a 5 cent problem.

stlrj · 02-14-2006, 05:18 PM

Mixture is also pretty basic and a good place to start.

ianc · 02-14-2006, 06:35 PM

If it's black, it can be either oil or gas. Oil will tend to look a little shinier than gas.

If it's oil, it will be getting into the combustion chamber from either the guides or the oil ring.

Adjust the valves, then do a compression test. If the compression is low on that cylinder, it may have overheated at one time. Squirt oil into the cylinder and retest. If the compression goes up significantly, then the rings are not good.

If the compression is good, the oil ring could be stuck or broken. Try running a couple of tanks of Techron through it and drive the crap out of it If it's only stuck, that may free it up. Keep a close eye on your oil consumption. If it's guides, you're looking at a top end. One or two guides out of 12 would be unusual, unless that particular cylinder overheated.

If the fouling looks like gas, the injector may be sticking open, or you don't have spark, although you would probably notice if one cylinder wasn't firing. Test to make sure you're getting a healthy spark at #6. If you have a good spark, pull all your injectors and bring them to your shop to be tested.

Let us know what you find.

ianc

ap911 · 02-14-2006, 08:51 PM

Thanks for everyones input. I am giving up and will let Power Tech in NJ get a crack at it. I will update the board as to what they find so that it may help somebody else down the road (so to speak).

mschuep · 02-15-2006, 05:50 AM

I would be happy to help you with the valve adjustment, if you decide to tackle it yourself...I've done it a couple times. Let me know what powertech finds out and how your experience goes, I have heard good things. I work in whippany and live in flanders

stlrj · 02-15-2006, 09:02 AM

Engine hesitation? Valve adjustment? Is there a connection?

PatrickB · PatrickB's Garage

AP-

I chased through the same problem for almost 2 years before resolving it... Mine was almost like hitting a rev limiter, but at 3-4k rpm's. Once you felt it, you could throttle up, and it would pass after about 500 rpm's, and be strong above that... Intermittent, and constantly changing what rpm it would occur...

Check the search option on this site, and put in engine hesitation, or rough running...

Personally, I think I went through every angle... Valve adjustment, spark plugs, wires, new distributor, coil, CHT, flywheel sensors, o2 sensor... Checked for proper fuel pressure. New intake manifold gasket, all new vacume lines, new ground strap, battery. Swapped 2 different working DME's, AFM's... Pressure tested intake manifold for leaks...

All to no avail... Problem would be intermittent. Sometimes only when hot, or only when cold... Problem would migrate to different rpm's, but usually you could drive through it after 4500 rpm... In the end, it was pretty much all the time...

The 2 last thing's left... injector's, and engine wiring harness... I finally broke down and bought the injector's ($145 each at PP.) The car has NEVER run better!

My suggestion to you - If you have one particular cylinder you feel is just a bit off, pull that injector, and replace it. If it runs better, replace the rest of them...

I hate to admit it, but IanC might be on the right track... My vote is for a bad injector...

ap911 · 03-30-2006, 10:18 AM

In order to help those with a similar problem I am posting the fix to the above mentioned problem.

In the end it was a fuel injector.

The fuel injectors to cylinders #6 and #5 were eventually swapped. The problem then migrated from cylinder #6 to cylinder #5. I relpaced said injector with a new one and problem solved.

Seems simple in the end, but getting there was not easy.

FYI, There are two types of Bosch copper WR7DC plugs: Those made in India and those made in Germany. In my opinion, stick with the ones made in Germany.

Thanks for the help.