Visit our Twitter feed for more great content
MGExp

MG Engine Swaps Forum

WOT woes with 3.4L 60 deg V6

Moss Motors
AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor

lagerratrobe Roger Andre
Seattle, WA, USA   USA
Hi All!

I am amazed at the cars I've seen in this forum. They are awesome! I have learned a ton about the GM 60 deg V6 from all of you and am hoping you can give me some troubleshooting advice. Full disclosure, I don't own an MG, but I do own an '84 S10 Blazer with a 3.4 liter GM crate engine. When I bought it, it didn't run at all and I have slowly been nursing it back to life. It's main problem was that it would start for a second and then die. This appears to have been due to a faulty ICM. After replacing it with one from the junkyard, that problem went away. I also replaced the Varajet carburetor with a Weber 38 DGES because I could not get the idle circuits clean enough to work properly on the old one. Generally speaking, I am very happy with the swap. I am using the stock S10 intake manifold with an adapter plate and have removed the warming grid from the intake.

I really like this year of S10 because there is almost no computer control on it at all. The distributor is a regular old vacuum advance HEI model and there is no crank position sensor, O2 sensor or any other engine management that I could find. I've eliminated the AIR system, smog pump and air conditioning and am running the engine with the EGR closed. I may decide to re-enable the EGR though, as I think it might be beneficial at keeping the engine temperature down on longer trips. We'll see, but for the most part I am extremely happy with this engine. I do however have one issue that I'm having trouble identifying, a very noticeable stumble or hesitation after running for more than a second or 2 at WOT.

This manifests itself most easily by downshifting into 2nd at 40 MPH and nailing the gas. When I do that, the engine starts to wind up properly and then coughs and lunges badly enough that I back off the throttle. Off-idle acceleration is excellent with no stumbling or hesitation until I hit 3000 RPM, or so. I welcome any ideas you have on this, my feeling is that it's either fuel starvation due to my electric fuel pump not keeping up, incorrect carb jetting (main jets either too lean or way too rich), or an ignition system that either has insufficient spark or incorrect timing. I intend to investigate each of these, however I am having the devil's own time finding some of the ignition parts I'm looking for.

Specifically, I am having trouble finding a replacement wiring pigtail that goes from the coil to the ICM. The original one showed signs of a short-circuit and was missing insulation along much of the wiring length. I found a replacement at the junkyard, but it also had very cracked wires and doesn't inspire confidence. Because the wires run into molded plugs on each end, I can't easily redo them myself and I'd prefer to just buy some replacement parts. What have you guys found as a good vendor for ignition parts on vacuum advance, non ECM, GM HEI distributors for these V6 engines? I don't have the money to do a full MSD 6-offroad system, but I would be willing to swap the coil, harness, ICM, and distributor pickup assembly to something a bit better. I think this must exist, but so far JEGS and other vendors have not yielded what I'm looking for.

Thanks in advance for any suggestions and for accommodating a fellow 60 deg V6 owner.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
260mgb Jim Nichols
Sequim,WA, USA   USA
Roger, You may have too much fuel pressure. I think you only need 3-4 for the Weber where the Holley likes 5-7. There was a link on the SAOCA board on the Weber carb. I'll see if I can find it.

260mgb Jim Nichols
Sequim,WA, USA   USA
Here is the link but also check your float level.

https://forum.ih8mud.com/threads/weber-38-dgas-info-settings-tuning.860402/

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
lagerratrobe Roger Andre
Seattle, WA, USA   USA
Thanks Jim, I'll have to look you up in Sequim sometime. My folks live out there too.

I've checked the float level and it's spot-on. A fuel regulator has been on my list, but since the pressure I measured initially from the electric pump was only 3 pounds, I thought I would be ok without one. What I'm not certain about is what the pressure drops to when I mash the gas. I've been thinking that I need to put a pressure gauge on a tee fitting and tape it to my windshield to test, but I haven't done so yet. My suspicion is fuel starvation, in which case a slightly higher volume and pressure pump running into a regulator would seem like the way to go. Does that sound right?

260mgb Jim Nichols
Sequim,WA, USA   USA
Roger, Have you checked the plug color? Could be not enough fuel at higher RPM's. Right now sunny Sequim has over 2 feet of snow with more coming. I am in AZ for 11 more months until I retire back there.

B-racer Avatar
B-racer Jeff Schlemmer
Shakopee, MN, USA   USA
1950 Willys Jeep Pickup "Ratrod"
1971 MG MGB ~ For Sale ! ~
2014 Dodge Charger
The S-10 uses timing retard via a knock sensor. If you have a vacuum advance, its from a 2.8 engine, which also has a timing retard system built in. Look up the factory timing process. You have to disconnect a fitting at the firewall that jumps your timing something like 10 degrees. I'm not sure it will work properly if you bypass this system, or if you use it. Catch 22. You're likely having timing issues. You also appear to be having fuel mixture issues, but until you fix the ignition which isn't going to be cheap because you put together a custom system that needs a custom advance curve, you shouldn't go adjusting the carb jetting. That comes after ignition is working properly, although you may want to find out if you;re going ridiculously rich or lean.



jeff@advanceddistributors.com

260mgb Jim Nichols
Sequim,WA, USA   USA
Jeff, I thought the early S10 and Jeep Cherokee (83-85) just had standard vacuum advance. Those are the distributors recommended for carb conversion for the GM 3.4 V6. Here is a Weber troubleshooting chart. I remember float drop setting is important too. I've had the 32/36 on four cylinder motors, not the 38. I put the Holley two barrel sideways on two small V6 motors.

https://forum.ih8mud.com/attachments/webertrouble-pdf.1085876/



Edited 2 time(s). Last edit at 2019-02-10 09:47 AM by 260mgb.

260mgb Jim Nichols
Sequim,WA, USA   USA
Roger, There was a guy on here that went to the older coil in cap HEI distributor from a 80-82 Chevy Citation 2.8 V6.



Edited 1 time(s). Last edit at 2019-02-10 10:33 AM by 260mgb.

lagerratrobe Roger Andre
Seattle, WA, USA   USA
Jeff and Jim, thanks for the ideas, I really appreciate them. I'll try to address some of the points you raised below.

* plug color: checked it once before after installing the Weber and it was "slightly lean". No glazing, but a touch grayer than brown. I'll check them again and will get fresh plugs and do some additional testing with a fresh plug run at a specific RPM. I think I'm also going to buy an AFR gauge, I've wanted one for awhile and it would allow me to more easily check the mixture over a wide range.

* knock sensor: I don't believe I have one, but it's possible. The distributor is from the original 2.8 liter engine that the SUV came with. I'm running vacuum advance directly from manifold vacuum, so am not sure how advance would be getting controlled otherwise (aside from the centrifugal weights), but I am a total novice with this engine and am completely willing to be wrong.

* ignition timing: yes, this very well could be the problem, I'll have to check. I believe if I hook a timing light up, I should be able to tell what total advance I'm getting by 2500 - 2800 RPM. I may not have enough for high RPM. What total timing are people running here on their 60-deg V6.

I appreciate the suggestion to focus on the ignition timing first though. At a minimum, I should be able to see how many total degrees of timing I'm getting right off the bat. I'll also measure the fuel pressure and get a regulator. I'll feel better with one of those installed.

260mgb Jim Nichols
Sequim,WA, USA   USA
Roger, I never messed with the stock ignition either when I upgraded to the 3.4 in my 85 S10. Or the 3.1 I put in the 85 Cherokee. I wonder if you should use ported vacuum instead of manifold? That shouldn't affect WOT though when vacuum would drop off. It would affect idle and cruise by having more timing.

B-racer Avatar
B-racer Jeff Schlemmer
Shakopee, MN, USA   USA
1950 Willys Jeep Pickup "Ratrod"
1971 MG MGB ~ For Sale ! ~
2014 Dodge Charger
Yes, use ported vacuum.
Mechanical timing is altered through the computer, not the vacuum timing. Read your service manual and figure out where that disconnect wire is on the firewall. Try setting timing at 10-12 BTDC and leave the wire disconnected. If you don't have the knock sensor hooked up (on the RH side of the block if I recall) its going to be really skewed. 34 degrees total timing is a safe place to start, with vac not included, until you get it closer to being dialed in.



jeff@advanceddistributors.com

. Hide banner ads & support this website by becoming a > Gold Supporting Member <

To add your reply, or post your own questions




Registration is FREE and takes less than a minute!


Having trouble posting or changing forum settings?
Read the Forum Help (FAQ) or contact the webmaster





Join The Club

Sign in to ask questions, share photos, and access all website features

Your Cars

1975 MG MGB MkIII

Text Size

Larger Smaller
Reset Save

Sponsor Links