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1985 C4 stalls after increasing RPM from Idle

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Old 02-11-2018, 05:41 PM   #1  
agillings
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Default 1985 C4 stalls after increasing RPM from Idle

FIXED 2/27/2018

My 1985 Stalls after I increase RPMs and will start right back up. My C4 is stock and has the smog pump removed. I got on it a couple of times ran fine the last time it felt like I was running out of gas. If I let it idle it would run. If I tried to give it some gas and would stall. It sat for about 4 days and runs fine now.

I Checked following:

Fuel pressure 39 psi with vac connected 49 without.
No Vac leaks
Replaced Fuel Tank assy (included Fuel Pump, sensor for gas gage and bag filter)
Checked IAC
TPS voltage
Did not change fuel filter yet

Does anyone have any ideas? I have the service manual (Red cover) nothing in there on this problem

Last edited by agillings; 02-27-2018 at 07:24 PM.
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Old 02-11-2018, 06:42 PM   #2  
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Hello there,
What you described on your post sounds like you have a "plugged" Catalytic Converter.

I had similar symptoms one day. When I started it the car it would start right up would idle perfectly but the moment the gas pedal was pushed the car coughed and sputtered but would not rev very well and even then barely above idle.

My car was a VW and they had a tiny tube that brought exhaust for the exhaust analyzer to read from. The eye opener for me was when the cap turned into a balloon and when I let off the accelerator the balloon would disappear. This proved that the catalytic was plugged on my car.

On my 1988 C4 I have a aftermarket "High-Flow" catalytic converter and I meet my states exhaust requirements. The performance ones are not that expensive.

Best wishes in getting your car to act normal again! I could be wrong but what you described sounds very much like my experience.
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Old 02-11-2018, 08:33 PM   #3  
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could also be plugged fuel supply. require fuel presdure gauge $20 ish to diagnose.
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Old 02-11-2018, 10:49 PM   #4  
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Originally Posted by VikingTrad3r View Post
could also be plugged fuel supply. require fuel presdure gauge $20 ish to diagnose.
Fuel Pressure was measured at 39 psi with vac hooked up 49 psi with no Vac
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Old 02-12-2018, 12:53 AM   #5  
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grab a temperature gun and check temps before and after the cat. closkeys suggestion most probable now.

if temps are close before and aft the cat, its flowing. if not, its plugged.

let us know
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Old 02-12-2018, 09:02 AM   #6  
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Originally Posted by VikingTrad3r View Post
grab a temperature gun and check temps before and after the cat. closkeys suggestion most probable now.

if temps are close before and aft the cat, its flowing. if not, its plugged.

let us know
Thanks I will give the temp gun a try. It will have to wait until this weekend
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Old 02-12-2018, 11:05 AM   #7  
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Quote:
Originally Posted by agillings View Post
My 1985 Stalls after I increase RPMs and will start right back up. My C4 is stock and has the smog pump removed. I got on it a couple of times ran fine the last time it felt like I was running out of gas. If I let it idle it would run. If I tried to give it some gas and would stall. It sat for about 4 days and runs fine now.

I Checked following:

Fuel pressure 39 psi with vac connected 49 without.
No Vac leaks
Replaced Fuel Tank assy (included Fuel Pump, sensor for gas gage and bag filter)
Checked IAC
TPS voltage
Did not change fuel filter yet

Does anyone have any ideas? I have the service manual (Red cover) nothing in there on this problem
So you are idling just fine and when you hit the gas, it seems to run out of fuel? Have you check the fuel pressure? A little high for vacuum line disconnected. Isn't it supposed to be at 43 at WOT? Have you check the fuel pressure at WOT yet? It should be able to hold steady with a load on it.

How did you check the IAC? Did you take the TB off, remove the top plate, remove the IAC and the IAC housing, clean all the passages and reassemble with fresh gaskets?

Since you are an 85, I am not sure what scanner will interface with the ECM so you may be stuck with getting codes and not actual live data. Might have to assume that everything is working in stock order.
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Old 02-12-2018, 11:17 AM   #8  
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also did u verify tps voltage throughout the arc? wonder if its dead right off the idle position?
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Old 02-12-2018, 09:02 PM   #9  
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Quote:
Originally Posted by agillings View Post
Thanks I will give the temp gun a try. It will have to wait until this weekend
I went out and started the C4 when for a short ride and as I was returning home the C4 started to stall when I advanced the rpm in drive.

Since the C4 has over 200K miles I went and changed the converter. With that much mileage the original converter can not be good.

Still have same issue, stall after increase in RPM. Also when the c4 is in park you can rev the engine, place in drive and try to increase rpm it stalls and pops through the air filter assy. I think the additional load on the engine causes the stall.

I can also cause it to stall and pop by taking the connector loose on the Mass Air Sensor and increase the RPMS

I have done all testing according to the Shop Manual

I have done all fuel pressure tests = 39 PSI when I shut the key off pressure goes to zero!
would this effect anything pressure is good.

TPS voltage adj
IAC operation check
Changed converter
Changed fuel assy in tank

Last edited by agillings; 02-12-2018 at 09:05 PM.
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Old 02-12-2018, 09:03 PM   #10  
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Quote:
Originally Posted by VikingTrad3r View Post
also did u verify tps voltage throughout the arc? wonder if its dead right off the idle position?
yes, all according to spec
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Old 02-12-2018, 09:25 PM   #11  
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do u have long cranks to start the car? like more than 1-2-3 cranks before starting?

when you did the fuel pressure test, did you tape the gauge to the windshield and watch what it does as you increase rpm to the stall?

im glossing over timing because you are saying you can drive it for a while and unless its the module usually timing is good or bad not intermittent.

when its dying, is it "fish biting" or @trailer jerking"?



but id like to know what the fuel pressure does AS YOU PRESS THE pedal.

The reason your gas pressure drops to zero with key off is either:
fpr toast (u said u pulled vac off im assuming u didnt see any gas coming out)
injectors dumping fuel due to clogged open or shorted signal
check valve in sending line shot (is that right guys? going from memory)

your symptoms sound like fuel supply. plugged fuel (lets enough gas through to idle but when call for fuel it bogs)
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Old 02-12-2018, 11:16 PM   #12  
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Quote:
Originally Posted by agillings View Post
I have done all fuel pressure tests = 39 PSI when I shut the key off pressure goes to zero!
would this effect anything pressure is good.
That is not a good sign. May be something is wrong. ASSUMING you are stock, that is. If you are not stock, maybe.

I don't recall if you have a cold start injector but you might. That means you have 9 injectors, any one or more could be leaking. Your FPR might be weak or your pump check ball isn't good or your FPR might have a weak spring or the pulsator is leaking fuel pressure. All of which contributes to the pump working hard to keep up. Under some conditions, it might not, hence the problem.

Lets try this. Take the fuel filler lid off to expose the fuel pump assembly. Get a helper for this. Soon as they turn the key, it should pressure up for 2 seconds. After 1 second, crimp off the sending line. If the pressure holds, the fault is between the crimp and the pump.

If the pressure doesn't hold, wait a few minutes, maybe 10 to 15? Repeat the test this time crimping off the return line. If the pressure holds, it is the FPR.

I believe the top line is the feed and the bottom is the return. The one line going to the left is the vent line so that isn't an issue.


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Old 02-12-2018, 11:19 PM   #13  
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Quote:
Originally Posted by agillings View Post
Changed converter
Changed fuel assy in tank
What converter? Catalytic or Torque?

With what? Did you just change the pump? Did you get the CORRECT hose to replace the pulsator? If so, where did it come from?
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Old 02-12-2018, 11:39 PM   #14  
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Quote:
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If the pressure doesn't hold, wait a few minutes, maybe 10 to 15? Repeat the test this time crimping off the return line. If the pressure holds, it is the FPR.

Further to Aklims comments, If pressure doesnt hold when both sending and return are crimped (after the pumps pressure cycling!) It could be the injectors or the fpr. if you pull the vac line and repeat the same test and no gas comes out of the fpr, then u have a leaky injector or a hole in your fuel system which im sure you would have noticed.


i know you tested the fuel system but i do think h should inspect the insta bleed off situation. I suspect it will be injectors flooding the engine.

this is why i was enquiring about a long start condition.

cheers and we can help u fix it.
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Old 02-14-2018, 08:11 PM   #15  
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[QUOTE=VikingTrad3r;1596579146]do u have long cranks to start the car? like more than 1-2-3 cranks before starting?

when you did the fuel pressure test, did you tape the gauge to the windshield and watch what it does as you increase rpm to the stall

im glossing over timing because you are saying you can drive it for a while and unless its the module usually timing is good or bad not intermittent.

when its dying, is it "fish biting" or @trailer jerking"?


but id like to know what the fuel pressure does AS YOU PRESS THE pedal.

The reason your gas pressure drops to zero with key off is either:
fpr toast (u said u pulled vac off im assuming u didnt see any gas coming out)
injectors dumping fuel due to clogged open or shorted signal
check valve in sending line shot (is that right guys? going from memory)

your symptoms sound like fuel supply. plugged fuel (lets enough gas through to idle but when call for fuel it bogs

Answers to you questions:
[LIST=1]
  1. Yes it starts quickly 1-2-3 started
  2. I checked the fuel pressure at Idle with Vac line connected = 39psi
  3. Vac line disconnected 49psi, No gas leaking from Vac line.
  4. I have not tested when stalling because I cant create it. That sounds dumb but it has happened 3 times.
  5. I changed the Fuel Tank unit. It was a complete unit, pump, sending unit. filter bag. It was from Rockauto =AC Delco
  6. 6 months ago I installed new Bosh injectors. The only injector that was not changed was the 9th injector (cold start) the C4 ran great!
  7. Yes the fuel pressure drops to zero when I shut the key off. Now fuel in oil.
  8. When it stalls it feel like I am running out of gas. The first time it happened I was at a half of tank. I thought the guage was wrong. got to a gas station filled up and same problem. Will idle fine and when I put it in gear it stalled. It is not doing it now.
  9. I was showing off and I floored it and it felt it was starving for fuel.
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Old 02-14-2018, 08:13 PM   #16  
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Originally Posted by VikingTrad3r View Post



i know you tested the fuel system but i do think h should inspect the insta bleed off situation. I suspect it will be injectors flooding the engine.

this is why i was enquiring about a long start condition.

cheers and we can help u fix it.
Thanks, it starts right up. The cold start injector is still installed
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Old 02-14-2018, 08:16 PM   #17  
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What converter? Catalytic or Torque?

With what? Did you just change the pump? Did you get the CORRECT hose to replace the pulsator? If so, where did it come from?
I purchased a new Catalytic converter. The orginal has 200 K on it. The engine only has 10K and the trans around 4k

The Fuel Tank unit came from Rock Auto it is an AC Delco and was a complete unit pump, fuel sending unit etc

Last edited by agillings; 02-14-2018 at 08:18 PM. Reason: add
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Old 02-14-2018, 08:23 PM   #18  
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That is not a good sign. May be something is wrong. ASSUMING you are stock, that is. If you are not stock, maybe.

I don't recall if you have a cold start injector but you might. That means you have 9 injectors, any one or more could be leaking. Your FPR might be weak or your pump check ball isn't good or your FPR might have a weak spring or the pulsator is leaking fuel pressure. All of which contributes to the pump working hard to keep up. Under some conditions, it might not, hence the problem.

Lets try this. Take the fuel filler lid off to expose the fuel pump assembly. Get a helper for this. Soon as they turn the key, it should pressure up for 2 seconds. After 1 second, crimp off the sending line. If the pressure holds, the fault is between the crimp and the pump.

If the pressure doesn't hold, wait a few minutes, maybe 10 to 15? Repeat the test this time crimping off the return line. If the pressure holds, it is the FPR.

I believe the top line is the feed and the bottom is the return. The one line going to the left is the vent line so that isn't an issue.


I have a cold start injector

There is a new fuel tank unit installed from Rock auto and is an AC Delco

I will try your pinch test and report back Thanks
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Old 02-14-2018, 10:04 PM   #19  
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oh so this is intermittent and rare. so you can go out and stomp on it and its fine 99% of the time?

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Old 02-14-2018, 11:37 PM   #20  
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Originally Posted by agillings View Post
I checked the fuel pressure at Idle with Vac line connected = 39psi

Vac line disconnected 49psi, No gas leaking from Vac line.

I changed the Fuel Tank unit. It was a complete unit, pump, sending unit. filter bag. It was from Rockauto =AC Delco

6 months ago I installed new Bosh injectors. The only injector that was not changed was the 9th injector (cold start) the C4 ran great!

Yes the fuel pressure drops to zero when I shut the key off. Now fuel in oil.

I was showing off and I floored it and it felt it was starving for fuel.
That means the pump is supplying pressure at idle.

That means the pump is supplying pressure at idle with a simulated WOT. We still need to know if it will do the same under load where fuel is really being consumed. Seems a tad high. Did you replace the fuel pressure regulator with a non stock one?

Did the pulsator get replaced with fuel rated hose at the time or not?

Runs great means nothing for this case. It could be the cause of the loss of pressure. It's supposed to spray extra fuel when it is cold starting. I'd have sent it out for cleaning after all this while it has been in service. When I do a project, I budget in a lot of "while we are here", within reason. I don't like cost overruns and sometimes still get caught. Will get more overruns if I didn't, I suspect.

If you have fuel in the oil, I suspect it is the 9th injector leaking after shutdown or you have poor compression. Regardless of "it runs great", which is something I don't have much use for, run a compression and leakdown test before your bearings get screwed up. That or change oil every time you drive it.

Not big on the "feeling" thing. Unfortunately, there is little that I know of personally that will scan an 85 besides a Tech 1 and even then, maybe not. Wish I knew someone with an 85 so I can test out my ALDLDroid on it.
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