Engine Hesitation

Hugh R · 10-02-2003, 03:26 PM

For the few weeks my 84 ROW Targa has had a slight hesitation on acceleration. Fuel and air filter, plugs are new and I've run Techron once or twice. It doesn't hesitated like one clogged injector, rather its the whole system. I step on the gas and it feels like none of the cylinders are getting gas, or spark, then it takes off just fine (it does this around 2500 to 3000 RPMs Any suggestions? DME perhaps?

marcesq · marcesq's Garage

1. Unplug O2 sensor and see what happens.

2. See if you can swap out your AFM with one that works as a test. Might be a bad spot on the barn door meter.

3. your guess is as good as mine

Hugh R · 10-02-2003, 08:57 PM

Marcesq:

I'll try the O2 sensor thing, but the AFM is what the "Air Fuel Meter?" I'm kind of new to pcars. Thanks for the reply.

VenezianBlau 87 · 10-03-2003, 04:22 AM

Hugh:

Does the exhaust smell rich? If so:

Maybe check the two vacuum lines that run to the back of the intake snorkel (in between the throttle body and air flow meter). If either is disconnected, engine will stumble at low rpms and run too rich (but smooth) at higher rpms.

Just feel around the back for any other loose lines.

Does it behave differently after driving for awhile?

Good luck,

Bob

Dan Owens · 10-03-2003, 04:51 AM

Has the O2 sensor been replaced? Does it run ok under heavy throttle between 2500 and 3500 but feel like it's fuel starved under normal throttle in that same RPM range? If that's the case I'd look at the O2 sensor needing to be replaced and then have the AFM adjusted for proper mixture.

marcesq · marcesq's Garage

Hugh: Sorry . . . . yep Air Flow Meter

Hugh R · 10-03-2003, 06:57 AM

Yeah, it smells a little rich, and Dan, it also does what you describe. If I disconnect the O2 sensor and get no change, wouldn't that mean the O2 sensor is suspect? I'll check all those things out. BTW, can I adjust the AFM myself. Thanks all for the help. I'll report back.

Dan Owens · 10-03-2003, 07:36 AM

Sounds like the O2 sensor is bad. The sensor is fairly easy to replace yourself. The sensor is about $180 I think if you go with the OEM and if you go with a generic and splice the connector on it's under $100. Once you replace that it should be okay unless the AFM needs to be adjusted for proper mixture. It's an easy adjustment for most shops and not very expensive. You should have a gas analyzer to set the mixture correctly. Do a search on O2 sensor and you should come up with plenty of info.

stlrj · 10-03-2003, 08:34 AM

Hugh...are the ignition cables the originals?

Joe

masraum · 10-03-2003, 08:46 AM

vacuum leak?

Hugh R · 10-03-2003, 09:04 AM

Don't know about the ignition cables (got the car a few months ago) but they're black and pliable and I didn't see any cracks or sparking (need to test the continuity). Will look for vacuum leaks as well. I get the rough idle effect when I take off the oil fill cap to check the oil (which I understand is normal) but will look for other vacuum leaks. Rotor and cap look good, very little pitting on the contacts.

marcesq · marcesq's Garage

Quote:

Originally posted by Hugh R
If I disconnect the O2 sensor and get no change, wouldn't that mean the O2 sensor is suspect?

No just the opposite

stlrj · 10-03-2003, 02:55 PM

How did the old spark plugs look?

Joe

stlrj · 10-05-2003, 03:06 PM

Did you put in Platinum plugs? If so, that may be your problem.

Joe

Hugh R · 10-05-2003, 04:54 PM

Old Plugs looked good.

stlrj:

The new plugs are Bosch which I bought from Pelican that they listed as being for my car. The plugs are not platinum (Pelican Part No. WR7DP) apprently from your post platinum is a problem? Why?.

Thanks.

SRISER · 10-05-2003, 05:29 PM

Hugh:

Okay, this may be a a sin on this board, but I would really like to see a pic of your DB4. I was thinking about an AM as a retirement gift (to me of course and from the military) which will occur in about 10 years.

Sam

Hugh R · 08:40 PM

Hey SRISER:

Here are a couple of pics of some of my toys, my Aston Martin and my 911 at Willow Springs (CA). Yeah, I know you guys don't like the bra thing on the pcar, but you have to drive up to Willow to understand the sand and debris that's out there. I've owned the Aston Martin DB4 since the early 70's (first car I ever bought) Here are a few pics of the engine when I rebuilt it last fall,

SmileWavy

stlrj · 10-06-2003, 12:16 PM

Hugh...nice DB4!

About Platinums, I don't know why they seem to give so many people problems, maybe it has something to do with the wrong heat range, who knows...but they seem too easy to foul.

Cheers,

Joe

Hugh R · 10-07-2003, 08:13 PM

Not that I want to impune (sp?) anyone on this board, but at about $160-$200 for an oxygen sensor, does anyone else have any thoughts on the Oxygen sensor being the problem? Thanks in advance.

stlrj · 10-08-2003, 10:05 AM

02 sensor? Probably not.

If it were my money, I would invest in a set of Magnacores and see if that takes care the problem.

Cheers,

Joe