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

Sorry if this is a stupid question but if there's a bad ignition switch in my Jimmy, is it possible that the engine will crank but fuel delivery will be sporadic or cut off? I'm starting to suspect the ignition switch as a
possibility for my poor cold starts. Thanks. Andrew.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Andrew-have owned many, many 95's and can't ever remember putting in a ignition switch in any-have put many in 97's but 95's, not many. Hard start-how long on the tune -up? Plugs, wires, cap, rotor, fuel filter, air cleaner. If that warrants doing, I'd do it-won't be bad money spent plus it may solve your problem. Besides that...Not costing much, if any, is fuel pressure check. Key on initial 2 second fuel pump pressure should be around 60 psi and then drop to 54ish when pump goes off and hold. Beyond that... temperature sensor possibly..in that this senson may be sending the wrong info to the computer thus leaning or richening out the initial fuel mixture. Hope this helps and let us know the results as we have many more suggestions! Good luck snipped-for-privacy@peru-motors.com
AWN wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Blazerman: thanks for the suggestions!
Ok... I am in the midst of repllacing both the ECT and the oil pressure sender (I have another post with some access for removal concerns). I have a decent scanner that shows no codes or strange freeze frame data, etc. The vehicle has a crate motor with maybe 50k km. The distributor along with cap,rotor, plugs, wires, pcv, coil and all newly replaced (LOF also done in last month). The throttle body and butterfly valve are spotless, the TPS was replaced and calibrated to factory specs. The gas tank and fuel pump are new also (although I hear horror stories of folks going through fuel pumps like undewear!). I did have a slight vac leak at the throttle body but that was just fixed with new ducting. Fuel pressure tests at 60psi with the pump and holds at 60 for over 15min (engine off). The pressure drops to about 50psi within 2 hours - I'm not outruling a dying pressure regulator or leaking nut kit/injector issue. I thought about leaving the gauge on all night to see if any excess pressure is lost. The O2 sensors test ok also. As well, the engine passes emissions maybe one month ago (cold start issue existed then also though).
I have been pining my money on a lazy ECT causing fuel starvation at the injectors but I am having a tricky time figuring out the best way to remove it.
Thanks and take care, Andrew.
in article snipped-for-privacy@q2g2000cwa.googlegroups.com, blazerman at snipped-for-privacy@peru-motors.com wrote on 1/21/07 4:27 PM:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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
AWN wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
in article snipped-for-privacy@v33g2000cwv.googlegroups.com, neex at snipped-for-privacy@cogeco.ca wrote on 2/10/07 12:21 AM:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

pump
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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Do you mean security as is OEM fuel/ign cutoff? This truck has no security features other than standard power locks. Thanks for all the recent responses.
Andrew.
in article 45d86d12$0$24744$ snipped-for-privacy@roadrunner.com, Kjun at snipped-for-privacy@hotmail.com wrote on 2/18/07 10:13 AM:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.