Help! New owner - what scanner to use for C4?

[85redvett]

Hi, recently bought 85 C4. Actually, better half bought it as my fathers day gift! Stumbles/hesitation when warmed up, seems to be intermittent...sometimes it goes other times it stumbles. Drain hole in gas filler was plugged, suspected some water in tank. Drained tank, ran some Heat through a tank to deal with left over water. Changed fuel filter(filled with crap), seemed to help a little, ran smoother stumbles less but still stumbles. Thinking maybe fuel pump, haven't checked fuel pressure yet. I've searched other posts and see things from fuel pump replacement, injector replacement etc...

I'm not sure this is fuel related so wanted to get some views on code scanners to buy to help with diagnostics. Also interested in any feedback on PC based scanners.

Any and all help appreciated!

 

[vetteoz]

Check FP first.
There are tests to do to check for leaking injectors or bad fuel pressure regulator .

Pull the codes to see if any faults are showing
Corvette C4 1984 - 1996 Electronic Control Module Recovering the Codes
This method will let you see the codes without a scanner.

Buy the factory service manual (FSM ); has all the diagostics to save you $$$
Always on eBay
1985 Corvette Service manual Repair Guide Used Nice:eBay Motors (item 170386990367 end time Oct-01-09 15:00:51 PDT)

If you want real time monitoring and datalogging all you need is a $60 cable , a old laptop and some free software
See
ALDL OBD1 OBD cable OBDI OBD2 engine codes

 

[85redvett]

appreciate the quick response and guidance along with the links. Been looking on ebay for FSM but haven't seen one, so thanks for that link! Plan to test FP this week. After that I'll pull the codes using the paper clip...

Thanks again!

 

[Schrade]

I've searched other posts and see things from fuel pump replacement, injector replacement etc...

Don't replace parts blindly. That's called the Fully Automatic Assault Wallet repair technique.

Get FSM and a multimeter.

Post up codes...

 

[85redvett]

Thanks Schrade, sage advice! Working on the FSM...

 

[85redvett]

Ok, i'm bidding on a manual. Checked the FP today. 32 lbs. Turn off, jumped to 34, 1 minute later 32, 1.5 mins 30, 2 mins 28, 2.5 min 26 etc....
Haven't done the code check routine yet... I believe i've seen that the FP should be between 36-39 lbs... So at 32 guess I have a pump problem? Strainer filled with junk? Filter is new, when i back washed it, it wasn't pretty....

 

[vetteoz]

Pressure is holding good which indicates no leakdown anywhere but as you note is low.
Should have 43 lb at the rail with vac line disconnnected
39lb at idle with line connected.
Pump weak or filter sock on pump clogged?

How to access pump
http://forums.corvetteforum.com/c4-...l-gauge-sending-unit-repair-tech-article.html

 

[85redvett]

Thanks again! I've got it mostly appart using the link, very helpful. Too cold up here to work on it tonight. I'm guessing the strainer is full of crap. It worked fine right up until the water incident.. and as I remember now.. I had run it very low on fuel so wouldn't surprise me if it picked up gunk....

 

[CorvetteArchives]

FSM's are ALWAYS CHEAPEST at the Publisher: Helm,inc.

Helm Incorporated: Product: 1985 Corvette Shop Manual

 

[Schrade]

FSM's are ALWAYS CHEAPEST at the Publisher: Helm,inc.

Helm Incorporated: Product: 1985 Corvette Shop Manual

confused

Define 'C-H-E-A-P-E-S-T', and 'A-L-W-A-Y-S'... :confused

i kant reed 2 gud, but $41, $36, $32, $79 < $82.

 

[85redvett]

got fsm coming. $40 on ebay, should be here next week. Put new pump and strainer in. Some improvement but think there is still a stumble. Kind of a rainy crappy day today so didn't really get a chance to punch it. Still need to check fuel pressure after new pump - got distracted by beer...tomorrow maybe.

 

[Schrade]

got fsm coming. $40 on ebay, should be here next week. Put new pump and strainer in. Some improvement but think there is still a stumble. Kind of a rainy crappy day today so didn't really get a chance to punch it. Still need to check fuel pressure after new pump - got distracted by beer...tomorrow maybe.

First test static pressure - leak down; compare to previous readings. Good job recording previous info. Most folks are scared of pencil and paper.

You don't really need to 'punch it' for anything. Closed loop idle quality is the MOST tell-tale indicator of state of tune.

Fuel pressure was holding pretty good like oz said, but maybe anyway hit all 9 injectors with a multimeter. Do them cold, then hot also. Remember, #9 will get NO signal on a closed loop motor.

AND, maybe do the static pressure bleed down with the fuel line capped BEFORE the FPR. This will show how much fuel the injectors are letting by. Then repeat with the line connected to the FPR, and compare, to see how much pressure is getting by the FPR.

Then do dynamic pressure tests...

 

[85redvett]

Thanks Schrade. Two questions (my mechanical background is sketchy..) to check the injectors with the meter, where on the injectors do I place the probes? Second, what/how do I "cap" the fuel line before FPR... I'm really hoping my FSM arrives shortly...

Thanks again for the guidance...
Rick

 

[Schrade]

I think Jon/FIC injectors posted a vid of an injector Ohm test in C4 tech/perf in the 'other' vette forum (can't link; I'm banned)

To remove the connector from the injector, push carefully in the middle of the locking clip, with your thumb, right near where the little orange bagtie is. This will make the sides move OUTward from the injector body, and you can then pull the sides away. WATCH the locking clip - the WILL go ballistic, and get lost...

Carefully remove the connector (THE WIRES WILL BE BRITTLE). then you'll see the 2 connector contacts to the injector coil. Put the probes on the multimeter (negative and positive doesn't matter - just make sure the multimeter is set to 'Ohms' / resistance).

Be careful of dirt.

 

[85redvett]

great pics. Found Jon's vid on youtube...very helpful. thanks again.

 

[85redvett]

great pics. Found Jon's vid on youtube...very helpful. thanks again.

OK, been away for a while. I've replaced the fuel pump. Here are findings with new pump. Ignition on - FP goes to about 36lbs and holds. Start engine FP drops to about 34lbs, increases to about 38lbs when given some throttle. Turn engine off - FP goes to 38lbs and holds. Stayed at that reading for minutes droping only a pound after about 5 minutes. Car still has the stumble although doesn't seem to be as noticable. Engine cold runs better then when warmed up. Starts easier also.

Haven't taken the ohm meter to the injectors yet. Plan to do this week.

 

[85redvett]

I think Jon/FIC injectors posted a vid of an injector Ohm test in C4 tech/perf in the 'other' vette forum (can't link; I'm banned)

To remove the connector from the injector, push carefully in the middle of the locking clip, with your thumb, right near where the little orange bagtie is. This will make the sides move OUTward from the injector body, and you can then pull the sides away. WATCH the locking clip - the WILL go ballistic, and get lost...

Carefully remove the connector (THE WIRES WILL BE BRITTLE). then you'll see the 2 connector contacts to the injector coil. Put the probes on the multimeter (negative and positive doesn't matter - just make sure the multimeter is set to 'Ohms' / resistance).

Be careful of dirt.

OK, been away for a while. I've replaced the fuel pump. Here are findings with new pump. Ignition on - FP goes to about 36lbs and holds. Start engine FP drops to about 34lbs, increases to about 38lbs when given some throttle. Turn engine off - FP goes to 38lbs and holds. Stayed at that reading for minutes droping only a pound after about 5 minutes. Car still has the stumble although doesn't seem to be as noticable. Engine cold runs better then when warmed up. Starts easier also.

Haven't taken the ohm meter to the injectors yet. Plan to do this week.

update: my injector connection is a little different. There is a rubber boot over the top and doesn't appear to be any space to grab the locking metal clip....

 

[85redvett]

All Is Good!

I managed to get the caps off the injectors and they all checked out good. Someone suggested I check the plugs. I should have done this a long time ago and would have except when I bought it my mechanic changed the plug wires out and, I assumed, the plugs. Turns out he didn't...my mistake. I changed the plugs - #8,#6 were fouled bad, and WOW...runs better then when I got it. The good news is replacing the pump wasn't a waste of money as it needed to be done anyway...so thanks again for all the help...likely saved me a pile of cash!

thanks again to all who helped - great site with great people!

 

[CorvetteArchives]

Don't replace parts blindly. That's called the Fully Automatic Assault Wallet repair technique.

Get FSM and a multimeter.

Post up codes...

And all this time I thought it was called "Pay and Pray"

Good job with the repairs...a slow reasoned approach does always "pay"...or not as case may be...

 

[CorvetteArchives]

confused

Define 'C-H-E-A-P-E-S-T', and 'A-L-W-A-Y-S'... :confused

i kant reed 2 gud, but $41, $36, $32, $79 < $82.

ADD.......................... "Compared to CORVETTE VENDORS":W

Schrade......Too weird you actually saved the page and circled the entries to provide "proof" then uploaded it! A statement wouldnt suffice?