oups59

Summer is almost here and tonight was the first ride in my 928

Car starts right up and idle fine

But when on the highway, I notice a slight hesitation under load (30-50% throttle ) between 1500 and 3000 RPM. Looks good at higher RPM.

No problem when cruising. Fuel pressure at idle is good.

It can be related to the fuel delivery. I will replace the fuel filter tomorrow.

Any other ideas where I should look ?

Lizard928

O2 sensor and MAF.

blitz928

Did you use a fuel stabilizer before putting her up for the winter?

oups59

MAF just arrived from Injectionlabs. O2 sensor unknown. Need to check.

oups59

Yes I did

oups59

I just replace the fuel filter. And I still have the Misfire -hesitation problem. Always between 1500 and 3000 RPM. Run well over 3000 RPM.

I checked the spark plug wires tonight. I try to see if there was any flash. Looks good

Will do the O2 tomorrow.

the flyin' scotsman

Luc........when were the spark plugs, rotors and distributor caps changed? May be worth checking.

Salut.

oups59

Hi Malcolm.

I checked the rotors and distributor caps this winter and they looks almost new. I cleaned them ( a bit of sand paper too). I will recheck to plugs tomorrow to be sure.

I was reading another thread on the subject and the temp II sensor was the problem. Will verify that tomorrow too.

I will also take a look at the ground connections.

Thanks.

oups59

O2 Changed. The old one was not working at all. The black and one white wire were cut

The car run better but there is still that hesitation - misfire between 1800-3000 RPM

I checked the temp II sensor and it is a bit out of spec. It does not go below 350 Ohm. The WSM say it should go, at 212 degree F, between 100 and 200 degree F. Can that cause a problem?

I will also recheck the spark plugs.

kraabel

I'm facing the same issues and I'm going for the O2 sensor next.

Lizard928

Luc, if the temp 2 doesnt go hot enough it would cause a rich condition which causes a slight flat spot, Leaness causes hesitation and jerkyness.

Kraabel, is this on the 86.5 or the 90?

oups59

OK. The temp II sensor is change.

It runs a bit better but I still have misses between 1500-3000 RPM. But less than before.

I will check again the coil ground connections tomorrow.Just to be sure.

Can a modified exhaust system be related to that problem? I have a SuperSprint competition exhaust (no resonator and only a small muffler - loud sound). I remember when I changed the muffler on my motorcycle, I had the re-jet the carburetor to obtain proper performance. But I believe that with EFI it will adjust itself. Right ?

the flyin' scotsman

Luc..........the computers should adapt to the exhaust.

I'd start with the basics.........fuel, air and oil filter change...........inspect/change spark plugs........rotors/ distributors/ wires. After all are confimed good move to the sensors including the MAF.

I suspect its fuel related..........filter/pump/injectors.

oups59

I rechecked the ground wires and there is no coil ground wire on the left side

Ben Allison

Had a similar problem on a 951 before - ended up being the TPS.