2.0l fuel injected engine surge starve cycle? Options

[jdlmodelt]

I finally got the ignition and fuel pump hooked up on my 76 2.0 L and the engine cycles between reving and stalling when I hold the pedal down to get a fast idle. What do I need to be checking now?

[tod914]

Pinched line, clogged filter, filter on backwards, lines routed wrong (engine bay feed and return swapped). Have you tried putting a pressure gauge on to see what it is? You can pull the line off the cold start valve and hook it up there. 29-30 pounds. Can also check inside your gas tank for crud and a clogged stainer sock. Valves adjusted properly? Timing and dwell correct? Idle air screw on the throttle body, have you tried turning that up? You also have an adjustment on your ECU. Clockwise enriches, counter clockwise leans. That typically has a melted in hashmark for where the factory setting is.

[tod914]

Double check your ignition wires on the coil as well as the rest of your spark plug wiring. If the wires on the coil are swapped your car will run like crap. A shop did that on my 75 years ago. Eventually fried the ECU before I figured out the problem.

[jdlmodelt]

Double check your ignition wires on the coil as well as the rest of your spark plug wiring. If the wires on the coil are swapped your car will run like crap. A shop did that on my 75 years ago. Eventually fried the ECU before I figured out the problem.

the points go to the negative of the coil and the condenser and +12V to the positive side?

[jdlmodelt]

Pinched line, clogged filter, filter on backwards, lines routed wrong (engine bay feed and return swapped). Have you tried putting a pressure gauge on to see what it is? You can pull the line off the cold start valve and hook it up there. 29-30 pounds. Can also check inside your gas tank for crud and a clogged stainer sock. Valves adjusted properly? Timing and dwell correct? Idle air screw on the throttle body, have you tried turning that up? You also have an adjustment on your ECU. Clockwise enriches, counter clockwise leans. That typically has a melted in hashmark for where the factory setting is.

where is the adjusting screw on the ECU? There is a trim pot on the wiring harness back near the rear of the passenger side of the engine with a wire disconnected.

I hadn't thought about the timing. Good call on that...I just assumed that the PO hadn't changed anything while the motor was out of the car but he did change all the vacuum hoses. SO, I'll check timing and all hoses while I'm at it.

Thanks for the refresher...I haven't had to tune an engine in years. I used to do it all the time.

[jdlmodelt]

Pinched line, clogged filter, filter on backwards, lines routed wrong (engine bay feed and return swapped). Have you tried putting a pressure gauge on to see what it is? You can pull the line off the cold start valve and hook it up there. 29-30 pounds. Can also check inside your gas tank for crud and a clogged stainer sock. Valves adjusted properly? Timing and dwell correct? Idle air screw on the throttle body, have you tried turning that up? You also have an adjustment on your ECU. Clockwise enriches, counter clockwise leans. That typically has a melted in hashmark for where the factory setting is.

where is the adjusting screw on the ECU? There is a trim pot on the wiring harness back near the rear of the passenger side of the engine with a wire disconnected.

I hadn't thought about the timing. Good call on that...I just assumed that the PO hadn't changed anything while the motor was out of the car but he did change all the vacuum hoses. SO, I'll check timing and all hoses while I'm at it.

Thanks for the refresher...I haven't had to tune an engine in years. I used to do it all the time.

The fuel pressure holds steady around 30psi at the driver's side injector fuel rail.

[tod914]

On the coil (I have a 74 2.0), green wire from condensor (-) , black w/purple stripe (-), all black wire (+). Your all black wire may have a red stripe. Look carefully, sometimes the stripes can fade. Dwell = 47 degrees + or - 3 degrees. I forget the point gap. Maybe someone will chime in or you can check your Haynes manual.
There are also 3 white ground wires that attach to the case just underneath the engine latch. Check those as well. Transmission ground strap that attaches to the underside body (trunk pan).

[tod914]

On the top left side of the ECU, is your adjustment knob. Usually has a rubber cover on it the size of a dime. Regarding your trim pot, that's not factory. The PO might of had that hooked up to the cylinder head sensor on cyl #3. Check to make sure that head sensor is hooked up. That also can cause running issues. Hope that helps. At least your fuel pressure is good.

[jdlmodelt]

On the top left side of the ECU, is your adjustment knob. Usually has a rubber cover on it the size of a dime. Regarding your trim pot, that's not factory. The PO might of had that hooked up to the cylinder head sensor on cyl #3. Check to make sure that head sensor is hooked up. That also can cause running issues. Hope that helps. At least your fuel pressure is good.

I have a wire connected to the cylinder temp. Not sure if it is the right one. There is what appears to be a brown wire in the bundle that resides near the distributor that I thought might go to some sort of sensor located behind the distributor towards the rear of the vehicle?

I'll check the wiring as described above and also try to determine what the trim pot in the wiring harness is all about. I've been hooking the less obvious wires to mating connectors in the same general vicinity. I know that is not a best practice but...where else would they go? Over on the driver's side near the front of the engine is another brown wire with a female spade connector behind the air pump. Not sure where that one goes.

[Spoke]

Can you take some pics of this potentiometer you're talking about? There was a trim adjustment on the ECU but not one in the wiring harness. May have been some bandaid by the PO.

BTW, how is the normal idle? Is it smooth?

How does the engine run if you try to go to a high RPM like 2k, 3k?

Does it run good enough to drive it?

[jdlmodelt]

Can you take some pics of this potentiometer you're talking about? There was a trim adjustment on the ECU but not one in the wiring harness. May have been some bandaid by the PO.

BTW, how is the normal idle? Is it smooth?

How does the engine run if you try to go to a high RPM like 2k, 3k?

Does it run good enough to drive it?

the idle is smooth but so low that it stalls out after 3-5 seconds. If I start it with not pedal and get it idling then try to give it some gentle pedal it immediately stalls out. So, I can't even get it out of the garage yet to try it out. I had it running enough last night with short idles to get the engine warm enough that coldness should not have been the issue. (IMG:style_emoticons/default/sad.gif)

[Spoke]

Can you rev it up to 2k, 3k and stay running?

How about a pic of that potentiometer?

[jdlmodelt]

Can you rev it up to 2k, 3k and stay running?

How about a pic of that potentiometer?

nope. When I got it to start with the pedal partially depressed I had to dribble a little gas in the intake to get it to start and then it revved around 2k for a few seconds and sputtered and nearly stalled and then revved back up again for a few seconds and then sputtered and then tried to rev again and stalled.

[DRPHIL914]

Can you take some pics of this potentiometer you're talking about? There was a trim adjustment on the ECU but not one in the wiring harness. May have been some bandaid by the PO.

BTW, how is the normal idle? Is it smooth?

How does the engine run if you try to go to a high RPM like 2k, 3k?

Does it run good enough to drive it?

the idle is smooth but so low that it stalls out after 3-5 seconds. If I start it with not pedal and get it idling then try to give it some gentle pedal it immediately stalls out. So, I can't even get it out of the garage yet to try it out. I had it running enough last night with short idles to get the engine warm enough that coldness should not have been the issue. (IMG:style_emoticons/default/sad.gif)

i have a 75 2.0 and had a similar problem. if you are running really lean, you may have a surge cycle like you described. The POT you are talking about is most likely someone put there because the CHT was out of spec and they were increasing the resistance to fool the ECU so that you can adjust the richness. have you tested your MPS yet? a bad MPS will cause lots of these problems. running rich will cause a slower idle but make sure timing i s spot on first. check the ohm reading of your CHT, make sure it is the right one and that is specs out for your car. my car would start and stall when i first go it because it would flood out, it was a bad MPS, but a rebuilt MPS sent to me that was set too lean was causing the idle surge you have, and i had to increase the richness setting and was good to go. - look at your spark plugs- are the sooty , or lite from running hot/ it really sounds like you are flooding out. DO a vac check on the MPS first.

phil

[jdlmodelt]

Can you take some pics of this potentiometer you're talking about? There was a trim adjustment on the ECU but not one in the wiring harness. May have been some bandaid by the PO.

BTW, how is the normal idle? Is it smooth?

How does the engine run if you try to go to a high RPM like 2k, 3k?

Does it run good enough to drive it?

the idle is smooth but so low that it stalls out after 3-5 seconds. If I start it with not pedal and get it idling then try to give it some gentle pedal it immediately stalls out. So, I can't even get it out of the garage yet to try it out. I had it running enough last night with short idles to get the engine warm enough that coldness should not have been the issue. (IMG:style_emoticons/default/sad.gif)

i have a 75 2.0 and had a similar problem. if you are running really lean, you may have a surge cycle like you described. The POT you are talking about is most likely someone put there because the CHT was out of spec and they were increasing the resistance to fool the ECU so that you can adjust the richness. have you tested your MPS yet? a bad MPS will cause lots of these problems. running rich will cause a slower idle but make sure timing i s spot on first. check the ohm reading of your CHT, make sure it is the right one and that is specs out for your car. my car would start and stall when i first go it because it would flood out, it was a bad MPS, but a rebuilt MPS sent to me that was set too lean was causing the idle surge you have, and i had to increase the richness setting and was good to go. - look at your spark plugs- are the sooty , or lite from running hot/ it really sounds like you are flooding out. DO a vac check on the MPS first.

phil

what and where is the MPS on these engines?
j

[DRPHIL914]

on the passenger side of the engine compartment - it has a vac hose attached ,
manifold pressure sensor- they fail eventually , either leaking due to lost seal, or the copper plate in side tears.

[jdlmodelt]

on the passenger side of the engine compartment - it has a vac hose attached ,
manifold pressure sensor- they fail eventually , either leaking due to lost seal, or the copper plate in side tears.

Aha! I'll take a look at that too. the wiring harness for that has a rectangular tombstone shape, with two adjacent corners rounded but the sensor itself has a socket with all 90 degree corners and the plug can be inserted in either direction. So...while I was trying both directions the entire plug body slipped off the four wires. Do you know what wire goes in which position? (IMG:style_emoticons/default/sad.gif)

[brant]

you mentioned the wire from the distributor earlier in this thread.

that wire in a brown sheathing has another one of what your calling a rectangular tombstone plug end... it picks up the signal from the fuel injection points and tells the injectors when to open

without it no gas

often one of those 4 wires will brake, causing 1 bank to get gas the other bank not too

check that connection carefully.
the MPS, CHT, and Distributor fuel injection points are all Very important to the fuel injection system.

you may want to spend 4 hours reading the brad anders website that details all of the fuel injection componenets and how to test them.

[r_towle]

read

http://members.rennlist.com/pbanders/DjetParts.htm

[jdlmodelt]

you mentioned the wire from the distributor earlier in this thread.

that wire in a brown sheathing has another one of what your calling a rectangular tombstone plug end... it picks up the signal from the fuel injection points and tells the injectors when to open

without it no gas

often one of those 4 wires will brake, causing 1 bank to get gas the other bank not too

check that connection carefully.
the MPS, CHT, and Distributor fuel injection points are all Very important to the fuel injection system.

you may want to spend 4 hours reading the brad anders website that details all of the fuel injection componenets and how to test them.

yes there is a wire from the wiring harness a single conductor with brown insulation. where do I plug that in?