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| Rough engine idle and hesitation; Need some expert help | |
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| Tweet Topic Started: Jul 14 2014, 07:08 PM (2,161 Views) | |
| sheananigans | Jul 14 2014, 07:08 PM Post #1 |
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I am no novice when it comes to engine repair so this COULD... be a pretty off the wall issue, but then again I could just be looking too hard at the problem to figure it out properly. Either way all help is appreciated and welcome, and really I just need some second opinions. So let me start by describing the issue. When the engine has reached proper temperature and is at idle, it will run very very rough. Not necessarily low... just rough. Also I will add that when accelerating from a dead stop the engine does something very odd... the torque output feels well... low in lower rpms, even for a metro. When I rev the engine and begin to release the clutch everything seems fine and the car begins to move, until it comes to the point were the clutch fully grabs and then the engine just falls flat on its face. After a split second of hesitation all power comes back. This issue is less prominent when accelerating hard in the higher rpms. In conclusion I believe my problem is two fold. I think the engine idle issue is related to the engine coolant temp sensor. This is a 94 with the upgraded OBD-I emissions so the sensor is located on the throttlebody. The voltage at the connector is 4.98V, I may be wrong but as I remember its supposed to be 5V or higher. Also while running at operating temperature the resistance of the sensor is 258 ohms. Does this value seem correct? I cant find my FSM to confirm. I just moved and its gone! Second I believe that my valve timing may be slightly off.... less than a tooth. I rebuilt my engine and when I did that I had the head milled. It was a bone stock engine and had never been rebuilt before but I am not sure of the head being milled would have changed the timing enough to make the torque curve the way it is... Also as a side note when I rebuilt the engine I put in brand new pistons. Which I... like an idiot did not weigh. I SHOULD have done a counterbalance check on them first. But because I did not I believe my engine runs rougher as a result. For example, when shutting off the engine the last few revolutions that the engine makes shake it pretty badly. Ready... set... alright everyone. GO |
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| Memphis metro | Jul 14 2014, 08:35 PM Post #2 |
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Check fuel pressure with a gauge. Consider replacing fuel filter and checking fuel volume output of the fuel pump. |
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| sheananigans | Jul 14 2014, 09:28 PM Post #3 |
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I have checked fuel pressure, I had problems but I fixed that by replacing the fuel pump and sock as well at the fuel filter and pressure regulator. I will note there are some air bubbles in the return line, ideally this shouldn't be but I'm not sure what the problem is. After replacing those components fuel pressure primes to 40 psi then after its started it runs at 35 psi. |
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| Memphis metro | Jul 14 2014, 09:32 PM Post #4 |
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Those numbers are too high for a metro. Specs here, http://geometroforum.com/single/?p=543442&t=4464045 |
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| sheananigans | Jul 15 2014, 12:33 AM Post #5 |
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I will have to check the pressures again and maybe check for restrictions in the return line. Any idea what the proper resistance reading for a coolant temp sensor is? |
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| sheananigans | Jul 24 2014, 08:40 AM Post #6 |
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Okay so I got a fuel pressure tester and got some new numbers. The old fuel pressure tester I was using must have been faulty. Fuel pressure primes to 30 psi and with engine on drops to about 23-25 psi. If I turn the key off it holds pressure just fine. I also noticed while driving when I would get the hesitation there was no change in fuel pressure. So now I'm suspecting ignition systems issues... Spark plugs all look good, they are fairly new and have a nice even honey colored coat on them with no erosion. Who thinks maybe a failing coil pack? This is hard to figure out as its so intermittent. Cap, rotor, and plug wires are are equally as new as the spark plugs . < 10000 miles Any word on the correct resistance for the CTS? Edited by sheananigans, Jul 24 2014, 08:43 AM.
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| clarkdw | Jul 24 2014, 11:12 AM Post #7 |
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CTS resistance is fine. It is within the range of what my 94 upgraded is at when warm. 4.98 volts is also well within acceptable limits. Valve timing off a full tooth might cause this problem but when I experimented with mine it did not do that even at one full tooth out. It was lazy but not falling flat. Fuel pressure seems fine. Falling flat on its' face like that could be caused by something preventing accelerator pump type enrichment. If you are cruising along at light throttle at higher rpm and mash the throttle does it do the same thing? Do you have a spare MAP sensor to try? They are hard to find and very expensive for that exact model. (Ask me how I know). I have a MAP sensor from a 95 on mine as a result of that and it has worked perfectly for several years. Not sure if a later one than 95 will work or not but you would likely have to change the plug on your harness and check the pin positions as they are different on different years. |
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| Silver2K | Jul 24 2014, 11:13 AM Post #8 |
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4.98 is close enough to 5V where I would not worry about it. Your multimeter or ground could explain the difference. The issue where the engine falls flat, that has happened intermittently on my car since I've owned it (10 years). I found it would happen more when the alternator belt was loose. Eventually I concluded I have a weak ignition system. A larger gap in the plugs made the problem worse. Recently I went to fine wire iridium plugs. For now that has fixed the issue. I would agree with your assessment that you may have a weak ignition system. Others might tell you to clean your grounds. |
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| myredvert | Jul 24 2014, 11:36 AM Post #9 |
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myredvert
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Good news. There's a 94 FSM in the forum library. Driveability and Emissions - Symptoms Section 6E2-B I hate to ask the obvious, but have you already checked for any stored codes and done a compression check? Edited by myredvert, Jul 24 2014, 11:36 AM.
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| sheananigans | Jul 24 2014, 01:11 PM Post #10 |
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If I drive at light throttle and then mash the throttle it won't hesitate or fall flat on its face. It only does that when moving out of a complete stop. Although while at a cruising throttle position if I back off the pedal at all it will almost have a rhythmic jerking to the deceleration. All my grounds are brand new and upgraded to heavier gauge cable. And compression is 190 psi crossed the board ![]() Wet it's 195 to 200 psi I could try the map sensor but I don't currently have a replacement. |
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| David95237 | Jul 24 2014, 02:24 PM Post #11 |
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Make sure the hose going to the map sensor isn't restricted. |
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| sheananigans | Jul 24 2014, 02:29 PM Post #12 |
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All of my vacuum lines are brand new and I checked that I could blow air through the restrictor pill on that line. All clear... Unless maybe its clogged inside the throttle body somewhere. I will try testing the vacuum on that port. Oh and I forgot to add, no mil, no stored codes. And the mil does light up with key on but turns off after ignition on, as it should. Edited by sheananigans, Jul 24 2014, 02:31 PM.
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| nwgeo | Jul 24 2014, 02:45 PM Post #13 |
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Wow, I have 94 as well. Bone stock. I have developed some of what you are saying over the last 6 months. My MPG has been erroading and as soon as I get a few minutes I am going to do a seafoam down the throat and also run FI cleaner through the FI. I hope this will take care of my issues. |
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| sheananigans | Jul 24 2014, 04:23 PM Post #14 |
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Hmm, so I read through the link you posted to the FSM. It looks like I need to test the map sensor and Ho2 sensor for functionality. I'm leaning towards either a faulty ignition coil or faulty map. Reason being is my Ho2 sensor is brand new. |
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| sheananigans | Jul 24 2014, 11:07 PM Post #15 |
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So I ran a vacuum check on the line to the map sensor. With my tee in before he restrictor pill I was running at about 15 hg. Its reading 20 on every other port so I put a cap on the map sensor port and teed it in to the vacuum line that comes off there very back of the intake, so I'll report back tomorrow with how it drives with this set up. |
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