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Username Post: engine cuts out and dies        (Topic#348669)
Pritchard 
Forum Newbie
Posts: 10

Reg: 08-03-16
12-12-17 06:10 PM - Post#2717739    

I have a 1988 C1500. I did the 305 to 350 engine swap in the spring and have idling issues when in gear since the swap.

All adjustments and measurements were taken once engine was up to operating temp.

The 350 engine: bored .060 over, flat-top pistons, ported heads, new roller cam, opened exhaust a little (3" pipe to rear), new fuel pump and filter, increased fuel pressure with regulator spring, using 350 injectors and knock sensor, and probably a few other things that I forgot...

If I set the idle below 1200 rpm, engine will stumble and die when I put it in gear. Engine runs really good other than at low idle. I have checked and adjusted the timing (~6 degrees) and the TPS is reading .55 volts with throttle closed. IAC cycles as it should. Can't find any vacuum leaks.

The new cam is not too aggressive, 196/206 duration @ .050, 0.431 int./0.451 exh., lobe separation 109ᵒ. It even said computer compatible. I am getting 21 inches of vacuum at the manifold.

I have been using the 305 chip until today. I put in a 350 stage 1 chip. Same thing at idle, maybe even worse. It is a Jet Performance chip. Not the best, but I wanted something close to stock and programmed for a 350.

I have searched for solutions all over the internet and tried several suggestions but nothing has helped. If you have any thoughts or suggestions to help get this thing idling at the correct rpm, I would be grateful.

Pritchard

1988 C1500


 
Low priced Genuine GM Auto Parts
CowboyTrukr 
"6th Year" Silver Supporting Member
Posts: 3821
CowboyTrukr
Loc: Salt Lake City
Reg: 06-20-09
12-12-17 10:33 PM - Post#2717755    
    In response to Pritchard

If you’re using a computer compatible cam, then base timing should be set at zero BTDC compression. You mentioned setting idle below 1200. How are you accomplishing that when the computer is supposed to do so with the IAC?

A little more info might help direct the solution.

Sounds like we have similar set ups but for the cam.

Do you happen to have a factory PROM chip? I’m surprised it even ran with the 305 chip in it.

Greg

'95 K1500 Z71 EC Short Step 5.7L+0.040/NV3500
'00 Explorer XLT 4.0 V6 Auto
'94 K2500 5.7 NV4500 ECLB - SOLD

"The only thing necessary for evil to triumph is for good men to do nothing" Sir Edmund Burke


 
scrambldcj8 
Senior Member
Posts: 2293

Loc: MA
Reg: 04-06-03
12-13-17 04:17 AM - Post#2717762    
    In response to Pritchard

.....and timing was checked with the timing wire unplugged at the firewall? I'll assume Yes...

Let us know how you like the Ramjet/HT383 cam in the 350. It shouldn't be a crazy deal to get running as it was also used in marine 350TBI's., I want to do one in a 406....83G20 will likely chime in with hands on experience with that very cam/application. Hang tight.



 
Pritchard 
Forum Newbie
Posts: 10

Reg: 08-03-16
12-13-17 11:42 AM - Post#2717808    
    In response to CowboyTrukr

Thanks for replying. I wish I had a factory PROM for the 350, but I don't. I'll try resetting the timing back to 0 and see what happens. Yes,the electronic timing advance wire is unplugged when setting the timing. I am adjusting the idle speed with the adjustment screw in the throttle body.

The engine ran surprisingly well with the 305 chip. My understanding is that it will cause a slightly rich mixture at idle because the 350 injectors are providing a little more fuel than the computer was programmed to do. I was really hoping that the 350 chip would help with the idle problem and give a little more performance, but not so far.

UPDATE
Reset the timing to 0 degrees when I got home. It did help a little. Now I can turn the idle down to 1050-1100 rpm without the engine dying under load. Still not what I was hoping for, but it is getting better.

Pritchard

1988 C1500


Edited by Pritchard on 12-13-17 02:06 PM. Reason for edit: No reason given.

 
CowboyTrukr 
"6th Year" Silver Supporting Member
Posts: 3821
CowboyTrukr
Loc: Salt Lake City
Reg: 06-20-09
12-13-17 07:54 PM - Post#2717868    
    In response to Pritchard

That's what I thought. There is no idle adjustment screw. You've changed the factory air setting. The IAC is fighting against you. Someone removed the tamperproof cover.

I'll see if I can find the procedure to reset the air gap setting.

Greg

'95 K1500 Z71 EC Short Step 5.7L+0.040/NV3500
'00 Explorer XLT 4.0 V6 Auto
'94 K2500 5.7 NV4500 ECLB - SOLD

"The only thing necessary for evil to triumph is for good men to do nothing" Sir Edmund Burke


 
CowboyTrukr 
"6th Year" Silver Supporting Member
Posts: 3821
CowboyTrukr
Loc: Salt Lake City
Reg: 06-20-09
12-13-17 08:38 PM - Post#2717871    
    In response to CowboyTrukr

Here are a couple of links to help reset the baseline idle.

https://itstillruns.com/reset-baseline-idle-g m-tbi...

http://www.pirate4x4.com/forum/general-4x4-dis cuss...

Greg

'95 K1500 Z71 EC Short Step 5.7L+0.040/NV3500
'00 Explorer XLT 4.0 V6 Auto
'94 K2500 5.7 NV4500 ECLB - SOLD

"The only thing necessary for evil to triumph is for good men to do nothing" Sir Edmund Burke


 
Pritchard 
Forum Newbie
Posts: 10

Reg: 08-03-16
12-14-17 07:46 AM - Post#2717889    
    In response to CowboyTrukr

I have done that procedure before. Just not since I replaced the chip. I'll try that this PM. Thanks for taking the time to help me.

Pritchard

1988 C1500


 
Pritchard 
Forum Newbie
Posts: 10

Reg: 08-03-16
12-14-17 03:36 PM - Post#2717948    
    In response to CowboyTrukr

Just tried resetting the baseline idle. Followed the procedures in the links. Still no better on lowering the idle. Engine cuts out before I can get the idle down to the recommended rpm. Something else must be a little off or mis-adjusted.

Question...does the IAC ever stop clicking? I let it click for more than 60 seconds and it was still clicking when I unplugged the IAC harness.

Other than the idle problem, the engine runs great. I might just have to live with it.

Thanks again to those who have taken the time to give advice and offer suggestions.

UPDATE
I just can't be happy without looking over this problem again. When I re-read the IAC/Minimum air setting procedure, I couldn't help but notice that I forgot to disconnect the battery to reset the computer. So I did that again this PM. While waiting for the computer to clear any codes, I find a vacuum leak in a hose from the throttle body. So fixed that and performed the procedure again. Cleared codes, plugged everything back in, drove around the block, put transmission in reverse to park, BAM engine dies. Upped the idle with the idle screw and called it a day.

Pritchard

1988 C1500


Edited by Pritchard on 12-15-17 02:59 PM. Reason for edit: No reason given.

 
MiragePilot 
Forum Newbie
Posts: 30

Loc: Fort Worth, TX
Reg: 08-18-16
12-18-17 08:00 AM - Post#2718342    
    In response to Pritchard

This data point is not Chevy related, but might be of use...?
My neighbor had a Honda CRV that had an unreliable idle after we replaced the timing belt (which had failed while the car was running). Long story short, the interference engine had damaged the valves when the timing belt snapped and 2 of the 4 cylinders had very poor/zero compression thereafter.
Once he replaced the cylinder head, the poor idle performance disappeared.

Based on that, you might want to do a compression check and make sure all the cylinders are operating like they should.

Peter


1996 Chevy Express 1500 conversion van (Starcraft Hi-Top Conversion)


 
65_Impala 
Very Senior Member
Posts: 3928

Reg: 12-29-02
12-18-17 07:22 PM - Post#2718385    
    In response to Pritchard

I don't recall ever hearing an IAC click. You sure it's working?

The IAC will increase the air to the engine when the rpm drops a bit. Still, even with the IAC not working it should not die when put in gear if idling at 1200rpm.

Overall, it sounds like you need to do some tuning to get the idle dialed in. Overall, your description of the engine modifications indicates it's been changed a fair bit from stock.



 
Pritchard 
Forum Newbie
Posts: 10

Reg: 08-03-16
12-20-17 06:37 PM - Post#2718617    
    In response to 65_Impala

I pulled the IAC and connected the wires. The pintle did start to extend, so I'm assuming that it is working.

I have the idle set about 1050 when not in gear, and all is going well. I guess the mods/changes to the engine are not liked by the computer. I'll keep at it though.

Pritchard

1988 C1500


 
Low priced Genuine GM Auto Parts
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