Re: 95 4.3 vortec (Jimmy) ignition switch question on fuel delivery (crossposted)

Feb 11, 2007 8 Replies

in article snipped-for-privacy@v33g2000cwv.googlegroups.com, neex at snipped-for-privacy@cogeco.ca wrote on 2/10/07 12:21 AM:


Ok here's the latest... I replaced the ECT and the IAT... ALthough I
> think the fuel economy may have gotten a little better, I still have
> the cold starting problems. I have replaced the fuel pump relay 3x
> with known working replacements. When the relay 'clicks' and the pump
> whirls, it will start on a dime. I still think that there may be a
> chance that a faulty ignition switch is causing this problem.
>
> As stated previously, fuel pressure tested over 60psi at the rail
> shraeder test port, the pump will run with 12V to the test connector
> under the hood EVERY time, the battery and alternator tested fine
> (battery over 12V and alt constant at just over 14.6V), all tune up
> stuff has been done (plugs, cap, rotor, wires, etc).
>
> I thought that either the ignition switch, crank sensor, or oil
> pressure sensor may be at fault here. Can anyone comment? I have a
> baby on the way as we speak (due date was yesterday) so I'd like to
> get this damn Jimmy off my to-do list).
>
> What else should I be checking?? I checked nearly every 5V reference
> sensor and they came back fine (slight adjustment to the TPS but that
> was unrelated).
>
> Thanks in advance!
> Andrew.
>
> blazerman wrote:
>> AWN-I'd lean towards the temperature sensor. If you have a scan tool
>> on a cold morning scan it and look at the temperature screen and
>> compare that to the ambient temperature-may cost only your time.(then
>> hopefully a sensor). Keep us posted. Certainly don't know the answer
>> to your problem for sure but at the moment I peresonally had had more
>> issues with this sensor than oil pressure senders. Also doubt fuel is
>> your issue based on what you've wrote but some injector(good quality)
>> may help. in case of a varnished injector. Sounds like your doing the
>> best you can-good luck and keep us posted when you get it so the rest
>> of us will know! snipped-for-privacy@peru-motors.com
>

Sorry to double post. I have a few tech questions if anyone wants to entertain them...

Does the 95 4.3L W series motor on this Jimmy SLT 4x4 have an accumulator/reservoir for residual fuel pressure capacity? As well, does this block use a 'cold start injector'? I have also pulled the intake manifold tuning valve and looked in with a light a mirror for clean, shiny hose connections, etc. to indicate a leak at an injector or the FPR (as stated there's no problem with fuel pressure that I can drill down). I have fuel and spark and no codes are printing currently with the engine running in perfect time, etc. I just cannot drill down this damn intermitent starting problem. Does this sound like a worn crank sensor??

Thanks and sorry once again for the duplicate rants. Andrew.

No.

No.

Not if you have spark when the no-start is occurring.

Thanks for the response. Do you have any ideas what else I should be looking into diagnostics-wise? The MAP reads dead on also at 28.9in Hg (with about +800 ft above sea level). I'm beside myself as to why the pump will power up with the test connector but not so every time with the ign (key in engine off). When it finally starts, it runs like a top. Thanks. Would it help to post the outputs from my scanner?? Andrew.

in article snipped-for-privacy@newsclstr02.news.prodigy.com, aarcuda69062 at snipped-for-privacy@sbcglobal.net wrote on 2/10/07 10:12 PM:

You need a wiring diagram and a test light to solve this problem. When no-start, check for voltage and ground at the pump and then work your way forward to the fuel pump relay and the ECM signal to it. Concentrate on any splices and grounds since thhat is where trouble usually shows up first.

Nope, doesn't sound like the problem is with anything that would be seen in the data stream.

Sounds like a fuel pump relay or perhaps the ECM is at fault!

No

OBD I and II both cycle the fuel pump relay on initial 'key on' for about a second and a half to initially pressurize the fuel rail. The relay then turns off and stays off until the computer either registers oil pressure and/or rotation via the crank sensor/distributor.

I would have to check a service manual but I believe 60 psi is a little high. Anyway, if the vehicle maintains fuel pressure during cranking then that rules out fuel pump problems. Move on to injector triggering and ignition.

Our intermittent starting problem occurred in high humidity, turned out to be a defective new part, distributor cap arcing only in high humidity would it short so bad as to not start.

"Charlie B" wrote in news:BKWdnb6qU61mQEjYnZ2dnUVZ snipped-for-privacy@centurytel.net:

actually i see 55 to 60 normally on the system being discusssed (keyon, engoff), dropping to about 52 with engine running....any security feature should also be considered...........kjun

Charlie, Thanks for the input. When you mention checking injector triggering are you talking about using noid lights? I guess the procedure for checking the poppets is a little different as they don't test like regular EFI systems as far as I know. I still can't for the life of me access the oil pressure switch. Any tips on this? Do I have to pull the plenum or the distributor? Thanks again! Andrew.

in article BKWdnb6qU61mQEjYnZ2dnUVZ snipped-for-privacy@centurytel.net, Charlie B at snipped-for-privacy@centurytel.net@centurytel.net wrote on 2/16/07 11:41 AM:

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