95 Jimmy 4.3 Vortec starting problems - weird

[jdmccright]

This is getting confusing dealing with two different truck setups *sigh*. The '93 using a TBI injection system and the '95 using a CMFI system...you cannot compare the two beyond their basic operation, but they both do utilize some of the same sensors and valves. I will retract the coment about the cold start valve...I was premature in saying there definitely was one on these trucks unless someone else can back me, but I cannot find one on any version of injection system for the Jimmy.

That being said, if the '95 starting issue is resolved then this thread should be closed. If not, then it seems the only things left to check are the injectors, the poppet valves, the spider unit itself, and the fuel pulsator. Something in the system isn't keeping the fuel lines pressurized.

For the '93, I would look at the injectors, regulator, . If you're cranking and you're not smelling ANY gas from the TBI throat, there ain't no gas goin' in...simple as that. A fuel pressure check would help to diagnose which end to look at.

[wb8yjf]

I can see why this is confusing...mine is a 4.3 CMFI Vortec. Took me awhile to finally get it right.

[Megs1082]

The 93 is also CMFI injected. 4.3 Vortec - Vin W.

[rlith]

Originally Posted by Megs1082

The 93 is also CMFI injected. 4.3 Vortec - Vin W.

Actually it's CPI (Central port injectected) wheras 96+ is CSFI/CMFI (Central sequential fuel injection, or Cental Multiport Fuel Injection if the upgrade has been don)

[wb8yjf]

Ok. Now I'm really confused. I thought mine was CMFI (1995). I have a central "control" in the intake with a spyder assy. attached to that. I replaced the regulator on the back of the "central" part per info. in the FAQ's. Please tell me exactly what I have! I don't wanna look too stupid....

Thanks!
Jon

[rlith]

Originally Posted by wb8yjf

Ok. Now I'm really confused. I thought mine was CMFI (1995). I have a central "control" in the intake with a spyder assy. attached to that. I replaced the regulator on the back of the "central" part per info. in the FAQ's. Please tell me exactly what I have! I don't wanna look too stupid....

Thanks!
Jon

Yours is CPI (Central port injection). It uses a central spider assembly that batch fires (fires all injectors at once)

96+ CSFI/CMFI is similar in concept but each injector fires individualy based on rotor position (165432)

[Megs1082]

according to the chilton I do have a 93 CMFI - we just verified tonight, and according to the chilton there is no CPI??????

anyway

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I took off the upper manifold, there is fuel sitting in the bottom of the fuel pump regulator side. This could be a problem. I'm not sure what this means...

Here are a few pics. Does anyone have any thoughts?

http://www.geocities.com/jvonengeln/gmc.jpg

http://www.geocities.com/jvonengeln/GMC2.jpg

http://www.geocities.com/jvonengeln/GMC3.jpg



also there is a thread dedicated to my problem, but no one has responded!?!?!?!?!?

http://www.automotiveforums.com/vbul...=575706&page=3

[excheezhead]

in a previous post on 96-up 4.3L with W code, gm uses 1 term, CSFI. if the customer complains during warrenty about rough idle/hard starting, there is a clean and inspect procedure.
if customer still complaines under warranty, there is a list of conversion parts that will re-fit it to CMFI. as old master and blazee have explained, the conversion does 1 main thing usefull, it eliminates the popet injectors with more reliable and less high maintenance injectors and a new MFI module. i have been trying to see it this bulletin turned into a factory upgrade and what year it started, but i have had no luck so far. i do know that my 2001 still has CSFI, and i plan to do the mod as soon as the outside temp. here in south florida drops, as i have no carport or garage, and i ain't paying 4 hours shop rate to put in 275USD worth of parts. the bulletin is fairly well illistrated and all the needed gm p/n's are there. the only part of the cleaning i cant do is the nitrogen bottle blow down, but if i do the mod, thats not needed. so, if you are medium mechanically inclined and want to eliminate the future hassle of popet injectors misfiring and needing extra maint., i checked gmpartsdirect, and the parts including oring sealer, cleaner and the spider assembly and mod are $275+-USD and shipping. my $o.o2, its worth it to get that off my mind for the next 50,000 mi's.

[rlith]

[quote=Megs1082]according to the chilton I do have a 93 CMFI - we just verified tonight, and according to the chilton there is no CPI??????

anyway

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look at the how-to that's posted...

Your pics don't work

Another reason I don't like chilton manuals...

CPI=Central Port Injection...92-95 4.3 motors

CSFI=Central Sequential Fuel Injection 96-2000

CMFI=Central Multiport Fuel Injection-2000-2004 Standard, 96-1999 if you had injection problems (clogged, stuck open) and had the system upgraded. This was actually a recall issue for california I believe.


This is a CPI motor and CPI unit.. See thread here for more pictures...http://www.automotiveforums.com/vbul...ight=regulator



CSFI



CMFI



(Note, the CMFI above is the 8 cylinder version, no diff in the 6 really except less 2 nozzles) CMFI will work in CSFI motors w/ the conversion kit

[wb8yjf]

OK, according to what I'm hearing and seeing, I have a CPI engine. THANK YOU guys for clearing that up for me! I used that info from the FAQ section to replace my regulator.

This place rocks....

[batkoach]

yes from your pix this is a CPI unit. if it was starting with a jump but not on its own with a new battery there is a possibility you are drawing to much current and the voltage is dropping down to around 10 to 9 volts during cranking and the computer will not function when voltage drops this low there for no fuel injection however you may still get spark because it starts with the ignition module then switches to bypass for computed timing once the truck starts. check with a vat-40 tester if possible or two meters to check amp draw and how low voltage goes when cranking and if it is dropping to the voltages above ( around 9 to 10 volts0 then your starter is drawing to much current . a normal starter should draw between 125 and 175 amps. if more and volts dropping then this would explain why is starts with a jump as it is getting the additional ampsand voltage from your wifes truck.at this point replace the starter. if this checks ok then the test for the cpi is as follows . check fuel pressure if between 55 to 60 psi with key on engine off this is normal then you will need to do a fuel volume test . most quality gauges have this. there will be a small dia. hose with a valve coming off the gauge. get a 1 QT motor oil bottle with the see through edge and place hose in bottle and disconnect primary connector at ignition coil and have someone crank engine. with a watch time the fuel going into the bottle for 30 seconds . in 30 sec's normal volume should always be 1 pint or 1/2 a qt. if this is what you have replace your CPI . if you have the pressure but insufficent volume then your regulator is working and you will need to replace your fuel filter and if that does not work your fuel pump is done. thanks for listening, john harrier 20 year master machanic in michigan.

[rlith]

Well, if you read at the beggining of the thread, he states it fires fine when he sprays starter fluid or gas down the throttlebody, he has a new pump, etc etc. Basically he has lost pressure somewhere. Either in the nut kit or regulator, the issue is not a voltage one, the issue is not getting fuel. The only thing at this point that could combine the two is if the CPI is completely shot or the connector is bad.

[wb8yjf]

What would be the benefit of converting to a CMFI type system as opposed to the CPI? I know one thing, the spyder assy. on the CPI units look a lot less durable than the CMFI judging from the photos. Can this be done? The $350 or so for that cheap looking spyder for the CPI is mighty pricey...

Just curious.

Thanks!
Jon

[rlith]

they're both durable...


To upgrade to the CMFI you would need to swap out the following with 96+

Heads
Lower intake
Upper intake
Throttle body
EGR system
Engine Harness
ECM
Various sensors

A few other things

[wb8yjf]

Well, that settles that. I'm sticking with what I have.

Thanks for the info!
Jon