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Username Post: 1991 5.7 misses when cold        (Topic#348797)
Sonny Baker 
Forum Newbie
Posts: 15

Reg: 12-21-17
12-21-17 08:37 AM - Post#2718660    

I need some help.
I have a 1991 c1500 5.7 tbi with 115,000 miles on it. The truck misses for about 30 seconds after start up when the outside temperature is below 50 degrees. I have done all I can think of to this point and need some others opinions. Here is the thing that is so weird to me. At start up when it is missing, there is no smoke to speak of from the exhaust. As soon as it warms up slightly (and quits missing), it smokes just as you would expect. It makes me think it is something to do with the EGR system, but I have thrown a ton of parts at it to no avail. I have no CEL and it is showing no codes.
The truck does have a cold air intake on it, if that matters.

Here is what I have done so far:
Set timing (advance wire unplugged)
Ran two cans of Seafoam through the intake (1 through brake booster and 1 through PCV line)
Checked all vaccuum lines the best I can without smoking it.

New parts I have installed:
Plugs and wires
Cap and rotor
Coolant temp sensor
EGR valve and control module
PCV valve
IAC valve
Throttle Position sensor
Fuel filter
Battery
Rebuilt the TBI

The engine runs perfect once warm and will restart and run perfect, until it cools off.
I am the second owner and purchased this truck in August this year. This problem did not exist until the weather cooled off.

Can anyone give me any advice as to what could possibly be the problem?

Thanks,
Sonny





 
Low priced Genuine GM Auto Parts
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3715
Chevytech
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
12-21-17 11:51 AM - Post#2718676    
    In response to Sonny Baker

Welcome to the board!

It could be leaking a little coolant into a cylinder when cold. If it gets a bad leak into a cylinder it will liquid lock and the engine won't turn when you go to start it.

Does it seem to be using a little coolant?

For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If your vehicle has been altered from stock, let us know about that too.


 
Sonny Baker 
Forum Newbie
Posts: 15

Reg: 12-21-17
12-21-17 03:40 PM - Post#2718698    
    In response to Chevytech

Thanks for the reply ChevyTech.
I don't seem to be losing any coolant and don't have any white ( coolant type) smoke at start up. To add to my original post, there is no real "exhaust smoke" coming out of the dual exhaust while it is running rough, although you can hold your hand over one of the exhaust pipes and feel pressure coming out. Once the miss smoothes out I get what I would call normal smoke for a cold start. The exhaust does smell quite rich to me though.

Another odd thing. I have pulled the cold air intake off and started the truck cold and I seem to hear quite a loud vacuum sound sucking through the throttle body ( as if the EGR valve is stuck open). When the engine smoothes out the sound goes away, or vice versa.
I have sprayed carburetor cleaner all around the intake and haven't been able to locate an intake gasket leak.
I keep going back to the EGR system, but as I said the valve and control module are both new.

Is there a vacuum source I am missing somewhere??

Thanks,
Sonny




 
stumppuller 
"7th Year" Gold Supporting Member
Posts: 814
stumppuller
Loc: Canada
Reg: 11-01-04
12-21-17 04:44 PM - Post#2718708    
    In response to Sonny Baker

A leaking EGR valve will cause a hard start when cold, as well as stumble on acceleration and stalling at idle if it opens when it shouldn't. Did you use an OEM Delco replacement? That said, I don't think the EGR is the issue.

The loud sucking noise with the air cleaner off is normal.

Check the vacuum hose going to the MAP sensor is in good condition.

Does this truck have the original Camshaft? A cam swap or higher than stock fuel pressure will cause this. If you think it smells too rich, check your fuel pressure and watch the injectors for leakage. Might want to take a look in the ECM just to be sure the previous owner didn't swap in some aftermarket PROM chip.

On my truck everything was fine with the new Cam and higher fuel pressure until the temps dropped below 0C (32F), then it wouldn't start without holding the throttle open slightly (shook and missed until warmed up a bit). Re-tuned for less choke fuel and all is well.

-91 Sierra C2500, now K2500
-81 Chev K20


 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3715
Chevytech
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
12-21-17 04:55 PM - Post#2718712    
    In response to Sonny Baker

I agree with stumppuller the it is unlikely an EGR problem.

On a cold engine the ECM will not send power out to the EGR solenoid to get EGR operation.

I also agree testing the fuel pressure with it running would be a good idea.

When the engine is started cold the IAC will be open farther and make the sucking sound you describe.

A very common vacuum leak on these TBI trucks is the base gasket right under the TBI unit.

I would double check the plug wires to make sure the firing order did not get messed up when new wires and plugs were installed. Also plug wires 5 & 7 should not be installed next to each other in the plug wire holders or cross firing can occur because of induction.

For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If your vehicle has been altered from stock, let us know about that too.


 
Sonny Baker 
Forum Newbie
Posts: 15

Reg: 12-21-17
12-21-17 05:58 PM - Post#2718719    
    In response to Chevytech

Thanks for the replies fellas.
I did not replace the EGR valve with an OEM, although I have since aquired a known good OEM that I can swap out.
As far as the cam I'm not really sure. I don't think that anyone has ever been into this engine though. I bought it from the original owners daughter after he passed away and the truck was owners "baby" so he had done a few mods over the years,but they are mostly cosmetic and bolt on parts.
Not sure about the ECM, I'll have to dig into that as well.
I have looked at all of the vacuum lines, but will definitely check the MAP system again.

Fuel pressure was going to be one of the next things I planned to eliminate, so I will go rent a gauge and get that checked.
I installed a new base gasket after I rebuilt the TBI, so I should be good there.

I will go back and verify the wires aren't crossed as I replaced them back in September (when it was warmer) and at that point the missing issue hadn't occurred yet. I replaced the cap,rotor,and wires at the same time because I wanted to change them all to the blue (in color)performance parts from Summit Racing. It is definitely possible that I got the firing order out of whack.

Would the firing order crossed or 5&7 cross firing go away so quickly as the engine warmed though?

I dunno, but I`ll check this first thing in the morning as this is definitely a possibility.

Thanks again for the info,
Sonny




 
rockfangd 
"4th Year" Gold Supporting Member
Posts: 2280

Age: 31
Loc: Utica ny
Reg: 04-13-10
12-21-17 08:06 PM - Post#2718729    
    In response to Sonny Baker

I would not worry about the ecm at the moment.
Those things are usually bulletproof on these.
Is the egr the right one? How did you determine the correct one?
Coolant temperature comes to mind. If the coolant temperature sensor on the intake is going bad it may give false readings to the ecm but as temp increases it may come into parameter and seem to work fine.
From what you describe it does not seem as coolant could be getting into a cylinder.
Dont forget these are common to the intake gaskets. So you may have a leak there

Old School GM fan FOREVER


 
Sonny Baker 
Forum Newbie
Posts: 15

Reg: 12-21-17
12-31-17 08:52 AM - Post#2719524    
    In response to rockfangd

Update.......
Here is what I have done and what I have found.

I have:
Removed wires cap and rotor. I polished the distributor stem and reinstalled cap and rotor. Reinstalled wires per the Service Manual and ensured 5 & 7 wires are routed apart from each other. Problem still exists.
I verified that timing is stil set @ 0 degrees with the EST wire disconnected.

I let the engine cool down and hooked up the timing light.
On cold start the timing is advanced so much that you cannot see the timing mark on the balancer and it is firing radically (based on the light) at #1 wire. As the engine starts to warm (30 to 45 seconds) the timing comes back to what I would say is normal at cold running condition and the engine smoothes out and idles perfect.

I let the engine cool again and disconnected the EST wire.
This fixed the problem. It was idling a little slow, but no stumbling or backfiring through the TBI.
I shut it off, reconnected the EST wire and restarted. Problem came back for about 30 seconds then ran smooth.

So the problem seems to be that something is advancing the timing way out of range on cold start for 30 to 45 seconds, then it comes back to normal and runs fine. The colder it is, the worse it is and the longer it lasts.

Any ideas?

Thanks,
Sonny



 
CowboyTrukr 
"6th Year" Silver Supporting Member
Posts: 3821
CowboyTrukr
Loc: Salt Lake City
Reg: 06-20-09
12-31-17 08:59 AM - Post#2719525    
    In response to Sonny Baker

Sonny, it’s normal for the computer to advance the timing.

That’s the purpose of having the timing advance lead unhooked to set your base timing. By having it at zero, the computer then knows how to advance or retard the spark.

Just as a quick check, which coolant temp sensor did you replace?



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


 
Sonny Baker 
Forum Newbie
Posts: 15

Reg: 12-21-17
12-31-17 09:30 AM - Post#2719527    
    In response to CowboyTrukr

I changed the one on top of the intake beside the thermostat housing.

It just seems to me that the timing is being way overadvanced,like more than 24 degrees as the timing mark is coming up underneath the water pump.
To watch this play out with a timing light, as the timing comes back to about 18 degrees over, the engine idle speed increases and the stumble and backfiring goes away and everything smoothes out and it runs fine.
It does this every time the engine is cold and if you let it run to normal operating temperature the restart everything is fine until it gets cold again.
The odd thing is that it doesn't do it long enough at cold start for the actual engine temperature to increase much at all and it seems to do it for about the same amount of time regardless of the ambient temperature.

Strange to say the least.

Thank you,
Sonny



 
bowtie44s 
Valued Contributor
Posts: 3811
bowtie44s
Age: 35
Loc: wv
Reg: 08-29-12
12-31-17 09:56 AM - Post#2719530    
    In response to Sonny Baker

Timing tape and an individual needle pointer is so much better than the factory pointer. It is marked 60°BTDC-TDC.

I'm with Greg, it sounds like a bad CTS. What brand did you use?

Jeff

'88 Chevy K3500, aluminum head roller cam 511in³ stroker 10.5:1 compression, 96 NV 4500, 94-98 grille, 305/70-16 (33x12) BF Goodrich KM2s, 91 cluster swap


 
Sonny Baker 
Forum Newbie
Posts: 15

Reg: 12-21-17
12-31-17 10:50 AM - Post#2719532    
    In response to bowtie44s

I used an Oreilly house brand (Borg Warner).
Do you feel that I should order an OEM and try that ?
I have unhooked it at cold start and you can tell the ECM goes full rich and it won't hardly run at all.

Thanks.



 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3715
Chevytech
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
12-31-17 10:55 AM - Post#2719535    
    In response to Sonny Baker

The timing being 24 degrees BTDC at idle with everything connected on a cold engine is about what I expect.

Is the new IAC working well and giving it a fast idle when started cold?

For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If your vehicle has been altered from stock, let us know about that too.


 
Sonny Baker 
Forum Newbie
Posts: 15

Reg: 12-21-17
12-31-17 11:11 AM - Post#2719536    
    In response to Chevytech

Yes, the IAC seems to be working as once the miss goes away and everything smoothes out, the engine goes to high idle and then slowly decreases as it warms up.

One of the things that keeps my going back to timing is that while it is missing and stumbling there is really no exhaust smoke coming out of the exhaust pipes to speak of.( It does have cat back duals)
As the stumble goes away, I get what I would call normal cold running smoke coming from the exhaust.
Seems it is not firing (timed) right and the exhaust is not being released when the exhaust valve is open, but more the intake valve.(first made me think it was an EGR valve issue).

Through it all, as soon as it smoothes out it runs near perfect through all driving conditions.
No miss, stumble, nothing at all.

Your thoughts ?



 
Sonny Baker 
Forum Newbie
Posts: 15

Reg: 12-21-17
12-31-17 12:18 PM - Post#2719544    
    In response to Sonny Baker

I just thought of something.

Since the engine does not stumble at cold start with the ESC wire disconnected,are there any other sensors that the ECM disregards with this wire disconnected and returns to a factory preset value?

Thanks,
Sonny



 
CowboyTrukr 
"6th Year" Silver Supporting Member
Posts: 3821
CowboyTrukr
Loc: Salt Lake City
Reg: 06-20-09
12-31-17 01:25 PM - Post#2719548    
    In response to Sonny Baker

Sonny,

One thought. Let’s verify that the harmonic balancer hasn’t slipped.

Tape a strip of masking tape to the balancer. Pull the plugs, then with a soft wire, straw, or such similar item inserted into cylinder 1, rotate the crank until the #1 piston vertical travel reaches the top on the compression stroke. Once the straw stops moving up, score a line on the tape at the zero point on the timing tab. Reverse rotate to the same travel point. Again, scribe the tape. Double check your marks one more time. Then, mark the mid point between the marks. If it’s not on top of the factory timing mark, then the balancer outer ring has slipped.

The reason I suspect this is that you’re saying it runs better cold when unplugged. It’s not supposed to be that way. It should run a little sluggish when properly set at zero and then sit happy as a clam once you plug the bypass back in.

Fast idle should kick in almost as soon as the cold engine starts.

The computer takes it lead from the CTS until the temp starts climbing above about 100-110 degrees. Then the IAC starts backing down to baseline idle. Once that happens, the MAP and O2 run the show.

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


 
Sonny Baker 
Forum Newbie
Posts: 15

Reg: 12-21-17
01-01-18 03:57 PM - Post#2719713    
    In response to CowboyTrukr

Thanks guys,
I looked at the balancer close today and can see no signs of slippage just by looking at it.
I am going to go with Greg's method this coming weekend to verify.
In the meantime, I ordered OE AC Delco spark plugs and CTS and am going to replace the NGK's and the house brand CTS.
At this point, those are pretty cheap checks I guess and maybe I have a defective CTS. Seems everything is pointing to that.
Can't thank you guys enough for taking the time to help.
I'll keep you posted on the results.
In the meantime, if anyone thinks of anything else I'm all ears .

Rockauto is loving me right now!

Thanks again,
Sonny




 
65_Impala 
Very Senior Member
Posts: 3928

Reg: 12-29-02
01-02-18 11:36 AM - Post#2719784    
    In response to Sonny Baker

A laptop and a diagnostic cable can be used to confirm the sensors are reading correctly vs just guessing at them being bad or swapping parts hoping to find an issue.

The 3 basic steps to troubleshoot an issue with an injected engine with no check engine light:
1. Check fuel pressure.
2. Check the ignition system is in good shape.
3. Connect to the diagnostic port and check that the computer is working and the sensors are reading correctly.

When there is a check engine light, the first step is to read the code.



 
Sonny Baker 
Forum Newbie
Posts: 15

Reg: 12-21-17
01-07-18 10:45 AM - Post#2720338    
    In response to 65_Impala

Update #2

I swapped the parts house CTS with an AC Delco as well as changed the plugs from NGK to AC Delco and the problem still exists. I checked for slippage of the balancer and best I can tell, it hasn't slipped.
Checked the timing again, and I am at 0 degrees with the ESC wire disconnected.

I tried to rent a fuel pressure gauge, but the Oreilly in my town had theirs on loan out as of this morning. Going to try again tomorrow.

Question though. Does anyone suspect fuel pressure since it starts and runs fine on a cold start with the ESC wire disconnected?
I guess it could take a minute for the fuel pump to warm up and pump the correct pressure, just curious of your thoughts. The fact that it backfires some has been pushing me to think ignition.



65_Impala...I don't have a diagnostic cable, but would like to get one. Do you have a recommendation as to where to get one ?

This truck is not my daily driver , but something I had been trying to find for several years.
I bought one of these new in 1992 when I was 20 years old and over the last several years I had wanted to get another one.
I found this one with just over 100,000 miles and in excellent condition since it had been garage kept as a toy for many years by the original owner. He passed away and I was able to buy it.
The whole way me getting this truck is kind of one of those weird stories you sometimes hear about.

Thanks guys,
Sonny





 
runamukker 
Forum Newbie
Posts: 7

Reg: 01-01-18
01-07-18 12:02 PM - Post#2720346    
    In response to Sonny Baker

  • Sonny Baker Said:

In the meantime, if anyone thinks of anything else I'm all ears .

Rockauto is loving me right now!

Thanks again,
Sonny




Have you looked at or considered a malfunctioning catalytic converter? That is if your truck has one...

You did write if anyone thinks of anything else


'92 K1500 Blazer 5.7 700R4
'94 C1500 Cheyenne 5.7 4L60e


 
Sonny Baker 
Forum Newbie
Posts: 15

Reg: 12-21-17
01-07-18 12:20 PM - Post#2720348    
    In response to runamukker

Hadn't really thought about The CC, but the truck does have one.
I'll have a look at it.

It only does this for about 30 seconds on a cold start with an ambient temperature below 50 degrees,but at this point anything is fair game!

Thanks for the tip,
Sonny



 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3715
Chevytech
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
01-07-18 12:23 PM - Post#2720349    
    In response to Sonny Baker

  • Sonny Baker Said:


Question though. Does anyone suspect fuel pressure since it starts and runs fine on a cold start with the ESC wire disconnected?
I guess it could take a minute for the fuel pump to warm up and pump the correct pressure, just curious of your thoughts. The fact that it backfires some has been pushing me to think ignition.

Sonny



If the fuel pressure is low it could have a dribbling fuel injector on start up. Like you I think an ignition problem fits the symptoms better.

I diagnosed a TBI m van that the only complaint was it started hard at times. I found only had 3 PSI of fuel pressure because of a broken regulator spring. The owner told me he had tested the fuel pressure and it was good. He tested the pressure by putting a gauge on the end of a disconnected line (Dead Heading) which is not the way pressure is tested on these TBI trucks. With the truck running it only had 3 PSI.

Yes, an ignition system failure is possible. The distributor module can fail in different ways.

When the ESC wire is disconnected it is in the base timing mode. Maybe your distributor module has a problem in the electronic spark timing mode until it warms up

When the engine starts the module is in the base timing mode, but as the engine starts the module switches to electronic spark timing, and the timing is adjusted according to a signal it receives from the spark (knock sensor) module while in the electronic spark timing mode.

1993 fuel & emissions manual puts the switch over RPM at approximately 450 RPM is some places, and 400 in other places, in the manual.

Many auto parts stores in my area will test the distributor module for free if you bring it in. Make sure when you install or reinstall the distributor module that you use heat sink compound under it. The compound helps dissipate heat from the module. Without it, the module will fail.

Also check to see if the distributor shaft wiggles sideways. On these distributors the housing/upper bushing area can get so worn out that the shaft will move sideways so far that the points on the pickup coil pole piece get hit by the reluctor points on the shaft. When this happens the ECM receives compromised signal for RPM and timing issues.

For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If your vehicle has been altered from stock, let us know about that too.


Edited by Chevytech on 01-07-18 12:24 PM. Reason for edit: Add more

 
Sonny Baker 
Forum Newbie
Posts: 15

Reg: 12-21-17
01-07-18 03:09 PM - Post#2720362    
    In response to Chevytech

Chevytech,
I checked the distributor for play when I changed the cap and rotar. Although I didnt put a guage on it, I am guessing I have about a 1/8 of an inch of side to side play (twisting) in it. About the same up and down. Would you consider this to be too much ?

I had someone else say they had similar issues and it turned out to be the ICM. I will have it checked or replace it to rule that out.

Thank you.



 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3715
Chevytech
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
01-07-18 04:12 PM - Post#2720369    
    In response to Sonny Baker

Some up and down movement of the distributor shaft is normal.

Some rotational movement of the distributor shaft is also normal.

If you can move the shaft from sideways, like from the passenger side to drivers side, that is not normal, and is the wear that is a problem.

For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If your vehicle has been altered from stock, let us know about that too.


 
Sonny Baker 
Forum Newbie
Posts: 15

Reg: 12-21-17
01-15-18 12:33 PM - Post#2721108    
    In response to Chevytech

Final update.......Got it fixed !
Turned out to be the ICM.

So, before replacing the ICM I rented a fuel pressure gauge and found I was holding 12 psi steady while running.
I also went ahead and replaced the parts house brand CTS with an new AC Delco, but the problem continued.

When neither of those worked, I replaced the ICM with a new Delco part and that seems to have done the trick.

One tip off ( I think ) was I found that on a cold start that if I let it run just long enough to smooth out, that if i shut it off and tried to immediately restart it that I would have to crank it for 3 to 5 seconds before it would start.
I did this with the fuel pressure gauge on it and it was holding 12 psi the whole time so I figured it had to be ignition.

I think the ICM was failing and on the restart it was not going in to bypass mode.

Thanks everyone for your time and all of your help,
Sonny



 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3715
Chevytech
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
01-15-18 02:57 PM - Post#2721121    
    In response to Sonny Baker

Excellent!

Thanks for posting an update on what fixed it.


For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If your vehicle has been altered from stock, let us know about that too.


 
rain_man_rich 
Contributor
Posts: 124

Loc: Grants Pass, OR
Reg: 02-09-14
01-15-18 03:32 PM - Post#2721124    
    In response to Chevytech

That's an interesting fix and great job for finding it. Well done. I'm trying to figure out how it made those problems and what test could have pointed to the facts in this case. I'm coming up empty.




 
65_Impala 
Very Senior Member
Posts: 3928

Reg: 12-29-02
01-16-18 05:02 PM - Post#2721226    
    In response to Sonny Baker

You could get a cable from Red Devil River

http://www.reddevilriver.com/aldl.html


You can also build one,

http://www.chevytalk.org/fusionbb/showpost.php?pos...


User TunerproRT to log the truck. Get the adx file from gearhead.efi. Find the PCM number on it and the code from the module inside or to the link below and look it up in the table for your truck. The adx files are in each thread.

http://www.tunercat.com/tnr_desc/ecm_sup.html





 
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