Strange pulsing when applying throttle - coils or injectors?

[Erics4569]

TLDR - how can I confirm whether a 'pulsing' when accelerating is due to bad coils vs. injectors? (or other)

Hi, in the past couple weeks my 1997 TR4 (260k) has started to do a strange "pulsing" when I apply [steady] throttle/gas... usually most noticeable when under 3000 rpm.

I thought it was clutch slippage (it's a manual), but when I brought it to a shop they said they didn't think it was the clutch (not sure how they ruled it out), and it was more likely the ignition coils gone bad and/or combination of OE/loosening control arms (which apparently the play could give the sense of "pulsing").

They couldn't fix it before I needed to drive head out of town, so I did a quick diagnostic of the coils. One or more of them were changed around 195k -- so only about 65k ago (I've heard they can last quite long). In checking the ohms, the primary readings were 1.2-1.3ohms -- which is above the 1.05ohm specified in the FSM, so I was planning on changing them. However when I checked my multimeter against actual 1ohm resistor, it also read around 1.2ohms, so I'm wondering if the multimeter is off and the coils are fine. I did notice a bit of corrosion on the pin where the plug wires connect to the coil and so cleaned it up (I'll be replacing wires as they probably have ~60k on them as well).

When driving out of town, I added Seafoam to gas when fueling up. Interestingly since getting to the mountains (~6000ft), I no longer experience the pulsing when accelerating (or it may be very subtle), but acceleration feels pretty anemic (could be normal for being at higher elevation).

However, I'm now wondering if the issue could have been dirty/clogged injectors and either A) the seafoam did the trick cleaning them, or B) something about higher elevation helps reduce whatever is causing pulsing.

I still plan on changing plugs & wires when I get back home, but would rather not replace coils that may still be fine, especially if they may not be the actual issue (worth noting: shop said they didn't see any codes from the OBD)

Are there any recommendations around how to further troubleshoot the issue, either while at higher elevation or once back a sea level? Many thanks

 

[Devbot]

Coils are easier and cheaper to replace so I don't see why not start there. Could be they're providing a weak spark and seafoam helped them ignite a/f because of increased volatility
Coils CAN last a while... if you get good ones. I just had to replace mine after <40k miles because one crapped out and gave me a misfire. Can't remember what brand but they weren't OEM

 

[96RedRunner]

Boots for coils when doing plugs n wires. Have new coil on shelf due to bad boot.

 

[phattyduck]

Its probably worth testing/checking the TPS too. A number of reports of surging and throttle control issues have been traced back to that.

-Charlie

 

[Erics4569]

I ended up replacing plugs, wires, and coils (since I couldn't get a consistent ohm reading on them and they were a bit out of spec) -- the pulsing is now gone. Thanks for your tips

 

[JoeT4R]

@ OP, glad to hear this resolved your issue.

I just want to add my experience with this for anyone who may encounter something similar. A few years ago I was on my way to the OBX and I remember my truck would exhibit this like jumping or "pulsating" feeling for lack of a better word right around 50 mph. It would do it consistently but only at that specific speed. Right before we went to the OBX I did new plugs (NGK) and wires (also NGK). Through a bit of research I came to the conclusion of replacing the coils since they were still the originals. I ordered new ones from RockAuto (Denso brand), replaced them, the jumping/pulsating was completely gone and has not returned since then.

When this was happening it was honestly barely noticeable but I'm pretty hypervigilant about how my truck acts. I've been daily driving it for over 11 years so I think I can say I'm well acquainted with how it should drive. The truck didn't have a check engine light on it so no codes indicated any bad coils or anything alike. Nor did I do any testing to see if they were okay. I just went ahead and replaced them because it was the last part of the puzzle & thankully it did the trick.